fetal presentation variable means

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Abnormal Fetal lie, Malpresentation and Malposition

Original Author(s): Anna Mcclune Last updated: 1st December 2018 Revisions: 12

• 1 Definitions
• 2 Risk Factors
• 3.2 Presentation
• 3.3 Position
• 4 Investigations
• 5.1 Abnormal Fetal Lie
• 5.2 Malpresentation
• 5.3 Malposition

The lie, presentation and position of a fetus are important during labour and delivery.

In this article, we will look at the risk factors, examination and management of abnormal fetal lie, malpresentation and malposition.

Definitions

• Longitudinal, transverse or oblique
• Cephalic vertex presentation is the most common and is considered the safest
• Other presentations include breech, shoulder, face and brow
• Usually the fetal head engages in the occipito-anterior position (the fetal occiput facing anteriorly) – this is ideal for birth
• Other positions include occipito-posterior and occipito-transverse.

Note: Breech presentation is the most common malpresentation, and is covered in detail here .

Fig 1 – The two most common fetal presentations: cephalic and breech.

Risk Factors

The risk factors for abnormal fetal lie, malpresentation and malposition include:

• Multiple pregnancy
• Uterine abnormalities (e.g fibroids, partial septate uterus)
• Fetal abnormalities
• Placenta praevia
• Primiparity

Identifying Fetal Lie, Presentation and Position

The fetal lie and presentation can usually be identified via abdominal examination. The fetal position is ascertained by vaginal examination.

For more information on the obstetric examination, see here .

• Face the patient’s head
• Place your hands on either side of the uterus and gently apply pressure; one side will feel fuller and firmer – this is the back, and fetal limbs may feel ‘knobbly’ on the opposite side

Presentation

• Palpate the lower uterus (above the symphysis pubis) with the fingers of both hands; the head feels hard and round (cephalic) and the bottom feels soft and triangular (breech)
• You may be able to gently push the fetal head from side to side

The fetal lie and presentation may not be possible to identify if the mother has a high BMI, if she has not emptied her bladder, if the fetus is small or if there is polyhydramnios .

During labour, vaginal examination is used to assess the position of the fetal head (in a cephalic vertex presentation). The landmarks of the fetal head, including the anterior and posterior fontanelles, indicate the position.

Fig 2 – Assessing fetal lie and presentation.

Investigations

Any suspected abnormal fetal lie or malpresentation should be confirmed by an ultrasound scan . This could also demonstrate predisposing uterine or fetal abnormalities.

Abnormal Fetal Lie

If the fetal lie is abnormal, an external cephalic version (ECV) can be attempted – ideally between 36 and 38 weeks gestation.

ECV is the manipulation of the fetus to a cephalic presentation through the maternal abdomen.

It has an approximate success rate of 50% in primiparous women and 60% in multiparous women. Only 8% of breech presentations will spontaneously revert to cephalic in primiparous women over 36 weeks gestation.

Complications of ECV are rare but include fetal distress , premature rupture of membranes, antepartum haemorrhage (APH) and placental abruption. The risk of an emergency caesarean section (C-section) within 24 hours is around 1 in 200.

ECV is contraindicated in women with a recent APH, ruptured membranes, uterine abnormalities or a previous C-section .

Fig 3 – External cephalic version.

Malpresentation

The management of malpresentation is dependent on the presentation.

• Breech – attempt ECV before labour, vaginal breech delivery or C-section
• Brow – a C-section is necessary
• If the chin is anterior (mento-anterior) a normal labour is possible; however, it is likely to be prolonged and there is an increased risk of a C-section being required
• If the chin is posterior (mento-posterior) then a C-section is necessary
• Shoulder – a C-section is necessary

Malposition

90% of malpositions spontaneously rotate to occipito-anterior as labour progresses. If the fetal head does not rotate, rotation and operative vaginal delivery can be attempted. Alternatively a C-section can be performed.

• Usually the fetal head engages in the occipito-anterior position (the fetal occiput facing anteriorly) - this is ideal for birth

If the fetal lie is abnormal, an external cephalic version (ECV) can be attempted - ideally between 36 and 38 weeks gestation.

• Breech - attempt ECV before labour, vaginal breech delivery or C-section

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Obstetric and Newborn Care I

10.02 key terms related to fetal positions.

a. “Lie” of an Infant.

Lie refers to the position of the spinal column of the fetus in relation to the spinal column of the mother. There are two types of lie, longitudinal and transverse. Longitudinal indicates that the baby is lying lengthwise in the uterus, with its head or buttocks down. Transverse indicates that the baby is lying crosswise in the uterus.

b. Presentation/Presenting Part.

Presentation refers to that part of the fetus that is coming through (or attempting to come through) the pelvis first.

(1) Types of presentations (see figure 10-1). The vertex or cephalic (head), breech, and shoulder are the three types of presentations. In vertex or cephalic, the head comes down first. In breech, the feet or buttocks comes down first, and last–in shoulder, the arm or shoulder comes down first. This is usually referred to as a transverse lie.

(2) Percentages of presentations.

(a) Head first is the most common-96 percent.

(b) Breech is the next most common-3.5 percent.

(c) Shoulder or arm is the least common-5 percent.

(3) Specific presentation may be evaluated by several ways.

(a) Abdominal palpation-this is not always accurate.

(b) Vaginal exam–this may give a good indication but not infallible.

(c) Ultrasound–this confirms assumptions made by previous methods.

(d) X-ray–this confirms the presentation, but is used only as a last resort due to possible harm to the fetus as a result of exposure to radiation.

c. Attitude.

This is the degree of flexion of the fetus body parts (body, head, and extremities) to each other. Flexion is resistance to the descent of the fetus down the birth canal, which causes the head to flex or bend so that the chin approaches the chest.

(1) Types of attitude (see figure 10-2).

(a) Complete flexion. This is normal attitude in cephalic presentation. With cephalic, there is complete flexion at the head when the fetus “chin is on his chest.” This allows the smallest cephalic diameter to enter the pelvis, which gives the fewest mechanical problems with descent and delivery.

(b) Moderate flexion or military attitude. In cephalic presentation, the fetus head is only partially flexed or not flexed. It gives the appearance of a military person at attention. A larger diameter of the head would be coming through the passageway.

(c) Poor flexion or marked extension. In reference to the fetus head, it is extended or bent backwards. This would be called a brow presentation. It is difficult to deliver because the widest diameter of the head enters the pelvis first. This type of cephalic presentation may require a C/Section if the attitude cannot be changed.

(d) Hyperextended. In reference to the cephalic position, the fetus head is extended all the way back. This allows a face or chin to present first in the pelvis. If there is adequate room in the pelvis, the fetus may be delivered vaginally.

(2) Areas to look at for flexion.

(a) Head-discussed in previous paragraph, 10-2c(1).

(b) Thighs-flexed on the abdomen.

(c) Knees-flexed at the knee joints.

(d) Arches of the feet-rested on the anterior surface of the legs.

(e) Arms-crossed over the thorax.

(3) Attitude of general flexion. This is when all of the above areas are flexed appropriately as described.

d. Station.

This refers to the depth that the presenting part has descended into the pelvis in relation to the ischial spines of the mother’s pelvis. Measurement of the station is as follows:

(1) The degree of advancement of the presenting part through the pelvis is measured in centimeters.

(2) The ischial spines is the dividing line between plus and minus stations.

(3) Above the ischial spines is referred to as -1 to -5, the numbers going higher as the presenting part gets higher in the pelvis (see figure10-3).

(4) The ischial spines is zero (0) station.

(5) Below the ischial spines is referred to +1 to +5, indicating the lower the presenting part advances.

e. Engagement.

This refers to the entrance of the presenting part of the fetus into the true pelvis or the largest diameter of the presenting part into the true pelvis. In relation to the head, the fetus is said to be engaged when it reaches the midpelvis or at a zero (0) station. Once the fetus is engaged, it (fetus) does not go back up. Prior to engagement occurring, the fetus is said to be “floating” or ballottable.

f. Position.

This is the relationship between a predetermined point of reference or direction on the presenting part of the fetus to the pelvis of the mother.

(1) The maternal pelvis is divided into quadrants.

(a) Right and left side, viewed as the mother would.

(b) Anterior and posterior. This is a line cutting the pelvis in the middle from side to side. The top half is anterior and the bottom half is posterior.

(c) The quadrants never change, but sometimes it is confusing because the student or physician’s viewpoint changes.

NOTE: Remember that when you are describing the quadrants, view them as the mother would.

(2) Specific points on the fetus.

(a) Cephalic or head presentation.

1 Occiput (O). This refers to the Y sutures on the top of the head.

2 Brow or fronto (F). This refers to the diamond sutures or anterior fontanel on the head.

3 Face or chin presentation (M). This refers to the mentum or chin.

(b) Breech or butt presentation.

1 Sacrum or coccyx (S). This is the point of reference.

2 Breech birth is associated with a higher perinatal mortality.

(c) Shoulder presentation.

1 This would be seen with a transverse lie.

2. Scapula (Sc) or its upper tip, the acromion (A) would be used for the point of reference.

(3) Coding of positions.

(a) Coding simplifies explaining the various positions.

1 The first letter of the code tells which side of the pelvis the fetus reference point is on (R for right, L for left).

2 The second letter tells what reference point on the fetus is being used (Occiput-O, Fronto-F, Mentum-M, Breech-S, Shoulder-Sc or A).

3 The last letter tells which half of the pelvis the reference point is in (anterior-A, posterior-P, transverse or in the middle-T).

(b) Each presenting part has the possibility of six positions. They are normally recognized for each position–using “occiput” as the reference point.

1 Left occiput anterior (LOA).

2 Left occiput posterior (LOP).

3 Left occiput transverse (LOT).

4 Right occiput anterior (ROA).

5. Right occiput posterior (ROP).

6 Right occiput transverse (ROT).

(c) A transverse position does not use a first letter and is not the same as a transverse lie or presentation.

1 Occiput at sacrum (O.S.) or occiput at posterior (O.P.).

2 Occiput at pubis (O.P.) or occiput at anterior (O.A.).

(4) Types of breech presentations (see figure10-4).

(a) Complete or full breech. This involves flexion of the fetus legs. It looks like the fetus is sitting in a tailor fashion. The buttocks and feet appear at the vaginal opening almost simultaneously.

A–Complete. B–Frank. C–Incomplete.

(b) Frank and single breech. The fetus thighs are flexed on his abdomen. His legs are against his trunk and feet are in his face (foot-in-mouth posture). This is the most common and easiest breech presentation to deliver.

(c) Incomplete breech. The fetus feet or knees will appear first. His feet are labeled single or double footing, depending on whether 1 or 2 feet appear first.

(5) Observations about positions (see figure 10-5).

(a) LOA and ROA positions are the most common and permit relatively easy delivery.

(b) LOP and ROP positions usually indicate labor may be longer and harder, and the mother will experience severe backache.

(c) Knowing positions will help you to identify where to look for FHT’s.

1 Breech. This will be upper R or L quad, above the umbilicus.

2 Vertex. This will be lower R or L quad, below the umbilicus.

(d) An occiput in the posterior quadrant means that you will feel lumpy fetal parts, arms and legs (see figure 10-5 A). If delivered in that position, the infant will come out looking up.

(e) An occiput in the anterior quadrant means that you will feel a more smooth back (see figure 10-5 B). If delivered in that position, the infant will come out looking down at the floor.

Distance Learning for Medical and Nursing Professionals

Position and Presentation of the Fetus

• Fetal Presentation, Position, and Lie (Including Breech Presentation)

Legal stuff

• Self Guided Tutorial
• EFM In-Depth
• Assessments
• Fetal Tracing Index

Electronic Fetal Monitoring

Basic and Advanced Study

Basic Pattern Recognition

Accurate fetal heart rate (FHR) assessment may help in determining the status of the fetus and indicate management steps for a particular condition.  In order to accurately assess a FHR pattern, a description of the pattern should include qualitative and quantitative information in the following five areas:

• Baseline rate
• Baseline FHR variability
• Presence of Accelerations
• Periodic or episodic decelerations
• Changes or trends of FHR patterns over time

These areas include fetal heart rate patterns with specific definitions and descriptions.  These definitions and descriptions are the terminology used by the National Institute of Child Health and Human Development and have been adopted by the American College of Obstetrics and Gynecology (ACOG) and the Association of Women’s Health, Obstetric, and Neonatal Nurses (AWHONN).

To appropriately interpret a fetal monitoring tracing, the systematic approach below should be followed:

• Evaluate the recording: is it continuous and adequate for interpretation?
• Identify the type of monitor used – external versus internal: second generation versus first generation.
• Identify the baseline fetal heart rate and presence of variability.
• Determine the presence of accelerations or decelerations from baseline.
• Identify changes or trends  in FHR patterns over time 

In addition to monitoring fetal heart rate patterns, information about the effects of labor on the fetus can also be learned by observing the pattern of uterine contractions. Uterine contraction patterns can provide information about the progress of labor. Also, because uterine contractions can affect placental exchange, evaluation of contraction patterns may provide clues as to the potential effects of the contraction rate and force on the fetus.

Uterine contractions are dealt with at the end of this section.

Demonstrated below is a picture from a typical EFM display and a sample EFM strip.

The mean FHR rounded to increments of 5 beats per min during a 10 min segment, excluding: Periodic or episodic changes Periods of marked FHR variability Segments of baseline that differ by more than 25 beats per min The baseline must be for a minimum of 2 min in any 10-min segment (NICHD)

In order to determine whether there are changes in the fetus’ physiologic status, a baseline heart rate must first be determined as a reference. All changes are therefore, based on a deviation from that fetus’ resting norm.

The normal FHR baseline should range between 110 beats/min to 160 beats/min. The baseline FHR is normally set by the atrial pacemaker and the beat-to-beat differences in the heart rate are governed by a balance between the sympathetic and parasympathetic branches of the autonomic nervous system.

As the central nervous system matures, the baseline FHR gradually drops, and the normal ranges for a mid-trimester fetus are between 150-170 beats/min. Parasympathetic tone becomes more dominant with advancing gestational age, and a post-term fetus may have a FHR between 110-120 beats/min.

Baseline Variability

Fluctuations in the FHR of 2 cycles per min or greater Baseline Variability Variability is visually quantitated as the amplitude of peak-to-trough in beats per min   Absent: amplitude range undetectable   Minimal: amplitude range detectable but 5 beats per min or fewer   Moderate (normal): amplitude range 6-25 beats per min   Marked: amplitude range greater than 25 beats per min  (NICHD)

In the normal fetus, there is an interplay between the sympathetic (acceleration) and parasympathetic (deceleration) nervous systems in the control of heart rate.  These systems exert their control via the cerebral cortex, the medulla oblongata, the sympathetic ganglia and the vagus nerve. The interaction between these systems results in a difference in the beat-to-beat intervals resulting in variability of the fetal heart rate tracing. In the term fetus, moderate variability is considered normal as it indicates a normally functioning central nervous system.  Conditions that alter the integrity of this neuro-cardiac axis, such as hypoxemia, result in loss of heart rate variability. Variability therefore, is the single most important indicator of an adequately oxygenated fetus.  Below is example of moderate variability.

Decreased or absent variability therefore represents some dysfunction in one or both of these systems, or in increased and dominant tone of one system over the other, such as during sleep cycles or due to the effects of drugs.

Causes of decreased variability include:

• Hypoxemia/acidosis
• Fetal sleep cycles
• Drugs (Analgesics, barbiturates, tranquilizers, phenothiazines, para-sympatholytics, anesthetics)
• Prematurity
• Arrhythmias
• Fetal tachycardia
• Preexisting neurological abnormality
• Congenital anomalies

Below is an example of minimal variability.  

Marked variability in the baseline FHR is present when the amplitude exceeds 25 BPM.This pattern (sometimes called a saltatory pattern) suggests acute hypoxia or mechanical compression of the umbilical cord and is often seen during the second stage of labor. When coupled with decelerations, this pattern is considered non reassuring and should warn the physician to search for, and correct, potential causes of hypoxia. Causes of marked (increased or saltatory) variability include:

• Fetal stimulation
• Mild, transient hypoxemia

Here is an example of marked variability:

The NICHD does not distinguish between LTV and STV, because they are viewed as a unit when the FHR is visually analyzed. Additionally, LTV and STV generally respond synchronously in response to changes in autonomic tone, and thus differentiation between LTV and STV generally does not provide additional information regarding the fetal oxygenation. There are some special circumstances where this not true; for example, a fetus with severe anemia demonstrates a pattern with absent STV but present LTV. This unique tracing is referred to as a sinusoidal pattern and will be discussed separately.

Acceleration

A visually apparent increase (onset to peak in less than 30 sec) in the FHR from the most recently calculated baseline The duration of an acceleration is defined as the time from the initial change in FHR from the baseline to the return of the FHR to the baseline At 32 weeks of gestation and beyond, an acceleration has an acme of 15 beats per min or more above baseline, with a duration of 15 sec or more but less than 2 min Before 32 weeks of gestation, an acceleration has an acme of 10 beats per min or more above baseline, with a duration of 10 sec or more but less than 2 min Prolonged acceleration lasts 2 min or more, but less than 10 min If an acceleration lasts 10 min or longer, it is a baseline change  (NICHD)

Accelerations of the FHR may be periodic (that is, occurring in relation to a contraction) or episodic (no association with a contraction). Most are episodic. These episodic accelerations are generally in response to fetal movement, with a need for increased perfusion, and therefore transiently increased sympathetic tone, or due to fetal stimulation, such as scalp stimulation with a vaginal exam, abdominal palpation, or vibroacoustic stimulation.

Periodic accelerations are those associated with uterine contractions and may be due either to fetal stimulation (particularly in breech presentation) or due to mild cord compression (that is, compression of the umbilical vein only).

FHR accelerations and good (moderate) variability are closely associated and sometimes may be visually indistinguishable, though both are reflective of a well-oxygenated fetus.

The presence of accelerations forms the basis of the nonstress test (NST). An NST is said to be reactive when there are at least two accelerations in a 20 minute period, along with moderate variability and no decelerations.

Below is an example of fetal acceleration:

Bradycardia

Baseline FHR less than 110 beats per min  (NICHD)

Fetal bradycardia is commonly associated with fetal hypoxemia. However, a number of causes must be considered:

• Maternal hypotension
• Hypothermia
• Maternal hypoglycemia
• Fetal bradyarrhythmias
• Complete heart block (Maternal SLE, CMV infection)
• Congential heart block
• Umbilical cord compression
• Amniotic fluid embolism
• Normal variation

As with fetal tachycardia, the bradycardic FHR must be analyzed for the presence of periodic changes and decreased variability. These findings are more consistent with hypoxemia. Some fetuses may display a bradycardic FHR but be completely normal. It should be remembered that the range of 110-160 does not represent all normal fetuses. The likelihood of a FHR in the range of 100-110 representing a normal variant increases as the fetus, and its nervous system, matures.

Early Deceleration

In association with a uterine contraction, a visually apparent, gradual (onset to nadir 30 sec or more) decrease in FHR with return to baseline Nadir of the deceleration occurs at the same time as the peak of the contraction  (NICHD)

An early deceleration and a late deceleration may visually appear identical. Both are smooth and curvilinear and appear to be a mirror image of the contraction. The distinction between the two is based upon the relationship of the deceleration to the uterine contraction (UC).

Early decelerations correspond, temporally, to the contraction and therefore exist only as a periodic change. Early decelerations are a benign finding caused by a vasovagal response as a result of fetal head compression by the contraction. Pressure on the fetal skull alters the cerebral blood flow and this in turn stimulates the vagus nerve. The heart rate is gradually decreased as the pressure of the contraction intensifies, and the deceleration gradually resolves as the pressure resolves. This pattern is generally limited to the active stage of labor. If the pattern is found in early labor, it may be associated with cephalopelvic disproportion (CPD).

Early decelerations have not been associated with fetal hypoxemia or acidosis.

Late Deceleration

In association with a uterine contraction, a visually apparent, gradual (onset to nadir 30 sec or more) decrease in FHR with return to baseline Onset, nadir, and recovery of the deceleration occur after the beginning, peak, and end of the contraction, respectively (NICHD)

Though late decelerations share the same morphologic shape as early decelerations, they tend to appear late, after the onset and nadir of the contraction.

Two varieties of late decelerations have been described, reflex and nonreflex. Reflex late decelerations are those which occur in the presence of normal FHR variability, whereas non-reflex late decelerations occur in association with diminished or absent FHR variability.

The classically described cause of late decelerations is uteroplacental insufficiency (UPI). In UPI, there may be a problem with a uterine perfusion or uterine activity or there may be a problem with the placenta, or both.

Uterine hyperactivity is associated with decreased time for intervillous space blood flow between uterine contractions. Similarly, maternal hypotension, even in the presence of normal uterine activity, will result in decreased volume of the intervillous space blood flow. Either of these factors may lead to a decrease in the maternal-fetal oxygen transfer.

Placental dysfunction, too, may lead to a decreased maternal-fetal oxygen transfer, and/or a smaller volume of placental reserve in proportion to fetal need.

Any of these causes may eventually lead to fetal hypoxemia and eventually myocardial depression. A vasovagal reflex leads to cardiodeceleration and continued hypoxemia may lead to lactic acidosis secondary to anaerobic metabolism.

Reflex late decelerations are thought to be due to vagal stimulation by chemoreceptors in the head in response to low oxygen tension. This is accentuated by the decreased oxygen transfer during a uterine contraction. The hypoxemia results in increased sympathetic stimulation leading to increased systemic vascular resistance. The response to this increased pressure is a vagally mediated decrease in heart rate. This dual reflexive response may explain the delay in the heart rate following a contraction. Reflex late decelerations are associated with normal FHR variability because CNS system is intact.

Nonreflex late decelerations, however, are associated with decreased or absent FHR variability. These decelerations are associated with a greater degree of relative hypoxemia and result in hypoxic depression of the myocardium coupled with the previously described vagal response. In reflex late decelerations, variability was maintained because the fetus was able to compensate, shifting oxygenated blood to vital organs (e.g., the heart), but in nonreflex late decelerations, the fetus is unable to compensate. It is these late decelerations which are more typically associated with fetal acidosis, and they are more commonly associated with placental dysfunction rather than uterine hypoperfusion or hyperactivity.

The causes of UPI are varied, and many are reversible:

• Uterine hyperactivity
• Maternal hypertensive disorders
• Placental abruption
• Placenta previa
• Maternal DM
• Chorioamnionitis
• Postterm gestation
• Maternal anemia, SS anemia, etc.
• Rh isoimmunization
• Maternal cardiac disease
• Maternal smoking

Tachycardia

Baseline FHR greater than 160 beats per min  (NICHD)

There are several causes of fetal tachycardia that must be considered, including:

• Maternal fever
• Fetal sepsis
• Drugs (Atropine, Vistaril, Phenothiazines, Beta-sympathomimetics)
• Fetal hypoxemia
• Tachyarrhythmias
• Fetal heart failure
• Severe fetal anemia, fetal hydrops
• Maternal hyperthyroidism

In general, tachycardia from any cause is related to an increase in sympathetic tone and/or a diminishment of parasympathetic tone. This means that one would normally expect an overall decrease in variability in association with tachycardia.

Fetal tachycardia is occasionally seen after a deceleration of the FHR, and in this instance is likely indicative of hypoxemia. This may be due to an attempt by the fetus to increase perfusion by increasing cardiac output or it may be due to increased catecholamine activity from the adrenal medulla in response to the stress of hypoxemia, when associated with a deceleration, and the loss of vagal tone.

Because the mechanisms for tachycardia related to hypoxemia are predisposed by some other signal hypoxic event, such as a prolonged deceleration, then isolated tachycardia, without evidence of periodic changes and in the presence of normal, though slightly diminished variability, is almost always due to a cause other than hypoxemia. Fever and/or chorioamnionitis are very common causes and fetal tachycardia may persist up two hours after correction of maternal fever.

Prolonged Deceleration

Visually apparent decrease in the FHR below the baseline Deceleration is 15 beats per min or more, lasting 2 min or more but less than 10 min from onset to return to baseline  (NICHD)

Prolonged decelerations can be caused by any mechanism which normally may lead to periodic or episodic decelerations, but the return to baseline is delayed because the stimulus or mechanism causing the deceleration is not reversed. This often is associated with hypoxia. Mechanisms which are less likely to resolve spontaneously are therefore more likely to be associated with prolonged decelerations, such as cord compression, profound maternal hypotension or hypoxemia, tetanic uterine contractions, or prolonged head compression associated with the second stage of labor. A FHR above 100 beats/min with good variability is tolerable, but a prolonged deceleration below 100 beats/min calls for immediate efforts at resolution and a drop below 60 beats/min becomes an obstetric emergency since it is almost always associated with fetal hypoxia.

Variable Deceleration

An abrupt (onset to nadir less than 30 sec), visually apparent decrease in the FHR below the baseline The decrease in FHR is 15 beats per min or more, with a duration of 15 sec or more but less than 2 min  (NICHD)

Variable decelerations appear morphologically different from either early or late decelerations. They are characterized by a sudden, abrupt drop in the FHT along with usually a similarly abrupt return to baseline. The shape varies widely, and they may appear as a V, U, or W. They may be either periodic or episodic. Often, there are small accelerations immediately before and immediately following the deceleration. These associated accelerations are often referred to as shoulders.

The classic mechanism described as the cause of variable decelerations is umbilical cord compression. Initial or mild umbilical cord compression results in occlusion of the umbilical vein, which is larger than the arteries and less rigid. This results in decreased venous return resulting in reflex tachycardia to maintain cardiac output. This explains the initial increase in heart rate (shoulder) preceding the deceleration. Further compression of the cord leads to occlusion of the umbilical artery, and the resulting increased systemic resistance, sensed by the baroreceptors, results in a protective reflex slowing of the heart rate. As the cord is decompressed, this series of events is reversed, and an acceleration may follow the deceleration (artery is decompressed but the vein is still compressed) prior to returning to baseline.

Variable decelerations are classified as severe when they last more than 60 seconds, fall below 70 beats/min, or have a drop of 60 beats/min below the baseline rate.

While umbilical cord compression is typically responsible for this pattern in the first stage of labor, it may also result from head compression during the second stage of labor.

Variable decelerations may be seen in the antepartum or early in labor if associated with oligohydramnios. Similarly, they may be detected after rupture of membranes, and in this setting they may portend cord prolapse, particularly if rupture of membranes occurred prior to engagement of the presenting part. During the descent phase of labors, typically between 8-10 cm cervical dilation, variables may be associated with nuchal cords causing cord stretch or compression, or with head compression associated with rapid descent and maternal valsalva.

Variable decelerations in the presence of normal FHR variability are not thought to represent hypoxia, but repetitive severe variable decelerations with diminished or absent FHR variability may indicate hypoxia.

Uterine Contractions

Two types of information can be ascertained from uterine contraction monitoring: quantitation of uterine activity (the strength of contractions), and contraction patterns (e.g. how many contractions, how often they are occurring). Assessment of contraction patterns is qualitative and can be performed with an external tocodynamometer or tocotransducer (Toco), whereas quantitative measurement of uterine strength requires an internal uterine pressure catheter (IUPC).

Qualitative patterns include regular uterine contractions, polysystole, tachysystole, paired contractions, skewed contractions, tetanic contractions, and uterine hypertonus.

In most normal spontaneous labors, contractions occur with a frequency of 2-5 minutes, and they may last between 30-60 seconds. The ascent and descent of the contraction are gradual and similar to one another. Contractions tend to become stronger and more frequent as labor progresses. Such a contraction pattern would be denoted as  regular uterine contractions, with a commentary on the frequency of the contractions (e.g., every 2-3 minutes).

A normal contraction pattern is demonstrated in the picture above with contractions every 2-3 minutes.    

Quantitative methods include Montevideo units (MVUs), Alexandria units, Active Planimeter units, Total planimeter units, and average rate of rise. Commonly, only MVUs are used in the US outside of research protocols.

With an IUPC in place, quantitative data can be measured, most commonly using Montevideo units (MVU). A Montevideo Unit is the sum of the intensity of each contraction in a 10 minute period (in mmHG). Adequate uterine activity is defined as a contraction pattern that generates greater than 200 MVUs. Studies have shown that this threshold is adequate for 90% of labors to progress. Among women in spontaneous labors, more than 40% have MVUs > 300 mmHG.  Baseline pressure, or resting tone, is the uterine pressure in mm Hg while the uterus is relaxed.

Types of Uterine Contraction Patterns

• Tachysystole (or polysystole) is defined as 6 or more UCs in 10 minutes without evidence of fetal distress.
• Hypertonus is either an abnormally high uterine resting tone (>25 mmHG) or MVUs > 400.
• Persistent tachystole classically with evidence of fetal distress (late decelerations, lost variability) but later accepted as even without distress (the same as modern definition of tachysystole), or
• A single UC lasting > 2 minutes which may also be called a tetanic contraction, or
• Uterine contractions occurring within one minute of each other. 

The most common cause of a tachysystolic, polysystolic or hypertonic contraction  pattern is  oxytocin or prostaglandins.

Other contractions sometimes described:

• Paired contractions, which are contractions that are coupled together, one after the other, then a prolonged gap in uterine activity occurs before the next set of paired contractions. This is sometimes thought to indicate cephalopelvic disproportion (CPD).
• A skewed contraction occurs when the crescendo and decrescendo of the contraction are not mirror images of one another. This relates to unequal relaxation of uterine muscle fibers and the clinical importance is not known.

Position and Presentation of the Fetus

• Fetal Presentation, Position, and Lie (Including Breech Presentation)

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Presentation and position of baby through pregnancy and at birth

9-minute read

If you are concerned about your baby’s movements, contact your doctor or midwife for advice immediately.

• If you baby is in a breech presentation, your doctor may recommend trying a technique called an external cephalic version to try and move your baby while they are still in the uterus for an easier birth.

What does presentation and position mean?

Presentation refers to the part of your baby’s body that is facing downwards in the direction of the birth canal.

Position refers to where your baby’s occiput (the bottom part of the back of their head) is in relation to your body.

If your baby is in a breech presentation , then position refers to where your baby’s sacrum (lower back) is in relation to your body.

People — including medical professionals — sometimes use these terms incorrectly. Sometimes when speaking about babies in breech presentation, the word ‘position’ will be used to refer to their presentation. For example, you may read information or hear people say ‘breech position’ instead of ‘breech presentation’.

What are the different types of presentation my baby could be in during pregnancy and birth?

Most babies present headfirst, also known as cephalic presentation. Most babies that are headfirst will be vertex presentation. This means that the crown of their head sits at the opening of your birth canal.

In rare cases, your baby can be headfirst but in face or brow presentation, which may not be suitable for vaginal birth.

If your baby is in a breech presentation, their feet or bottom will be closest to your birth canal. The 3 most common types of breech presentation are:

• frank or extended breech — where your baby’s legs are straight up in front of their body, with their feet up near their face
• complete or flexed breech — where your baby is in a sitting position with their legs crossed in front of their body and their feet near their bottom
• footling breech — where one or both of your baby’s feet are hanging below their bottom, so the foot or feet are coming first

Read more on breech presentation .

What are the different positions my baby could be in during pregnancy and birth?

If your baby is headfirst, the 3 main types of presentation are:

• anterior – when the back of your baby’s head is at the front of your belly
• lateral – when the back of your baby’s head is facing your side
• posterior – when the back of your baby’s head is towards your back

How will I know what presentation and position my baby is in?

Your doctor or midwife can usually work out your baby’s presentation by feeling your abdomen. They may also double check it with a portable ultrasound. Your baby’s presentation is usually checked around 36 weeks .

Your doctor or midwife will also confirm your baby’s head position in labour by examining your belly and using an ultrasound , and they may also do a vaginal examination . During the vaginal examination they are feeling for certain ridges on your baby’s head called sutures and fontanelles that help them work out which way your baby is positioned.

What is the ideal presentation and position for baby to be in for a vaginal birth?

For a vaginal birth, your baby will ideally be headfirst with the back of their head at the front of your belly, also known as being in the anterior position. This position is best for labour and birth since it means that the smallest part of your baby’s head goes down the birth canal first.

When does a baby usually get in the ideal presentation and position for birth?

Your baby will usually be in a headfirst position by 37 weeks of pregnancy. Around 3 in every 100 babies will be in breech presentation after 37 weeks.

Your baby’s position can change with your contractions during labour as they move down the birth canal, so their exact position can change during labour.

What are my options if baby isn't in the ideal presentation or position for a vaginal birth?

If your baby is in a breech presentation, your doctor may recommend a technique called an external cephalic version (ECV) to try and move your baby while they are still in the uterus . An ECV involves your doctor using their hands to apply pressure on your belly and help turn your baby to a headfirst position. It has a 1 in 2 chance of success and is a safe option in most pregnancies.

There is no evidence to show that alternative therapies, such as exercises, acupuncture or chiropractic treatments, help your baby change from a breech presentation to headfirst.

If your baby remains breech, your doctor may discuss having a breech vaginal birth. Not all doctors and hospitals offer this option. They may also suggest you birth your baby with a planned caesarean section .

If your baby’s presentation is headfirst but the position of your baby’s head is not ideal for labour, it can lead to a longer labour, and potential complications . The position of your baby’s head will often change as your labour progresses. If it doesn’t, sometimes you can still give birth without assistance, or you may need your doctor to help turn your baby’s head or help your birth with a vacuum or forceps .

Any procedure or decision for a type of birth will only go ahead with your consent . You will be able to discuss all the options with your doctor, and based on your preferences for yourself and your baby’s safety, make a decision together .

Resources and support

The Royal Australian and New Zealand College of Obstetrics and Gynaecology has a factsheet about the options available to you if your baby is in a breech presentation at the end of your pregnancy .

Mercy Perinatal has information on external cephalic version (ECV) safety and benefits if your baby is in a breech presentation at the end of your pregnancy.

The Women’s Hospital has information about the different presentations and positions your baby could be in, and how it can affect your birthing experience.

Speak to a maternal child health nurse

Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 or video call . Available 7am to midnight (AET), 7 days a week.

Learn more here about the development and quality assurance of healthdirect content .

Last reviewed: October 2023

Related pages

External cephalic version (ecv), malpresentation, breech pregnancy, search our site for.

• Foetal Version
• Breech Presentation

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Breech presentation and turning the baby

In preparation for a safe birth, your health team will need to turn your baby if it is in a bottom first ‘breech’ position.

Read more on WA Health website

Breech Presentation at the End of your Pregnancy

Breech presentation occurs when your baby is lying bottom first or feet first in the uterus (womb) rather than the usual head first position. In early pregnancy, a breech position is very common.

Read more on RANZCOG - Royal Australian and New Zealand College of Obstetricians and Gynaecologists website

External Cephalic Version for Breech Presentation - Pregnancy and the first five years

This information brochure provides information about an External Cephalic Version (ECV) for breech presentation

Read more on NSW Health website

When a baby is positioned bottom-down late in pregnancy, this is called the breech position. Find out about 3 main types and safe birthing options.

Read more on Pregnancy, Birth & Baby website

Malpresentation is when your baby is in an unusual position as the birth approaches. It may be possible to move the baby, but a caesarean may be safer.

Labour complications

Even if you’re healthy and well prepared for childbirth, there’s always a chance of unexpected problems. Learn more about labour complications.

ECV is a procedure to try to move your baby from a breech position to a head-down position. This is performed by a trained doctor.

Having a baby

The articles in this section relate to having a baby – what to consider before becoming pregnant, pregnancy and birth, and after your baby is born.

Anatomy of pregnancy and birth - pelvis

Your pelvis helps to carry your growing baby and is tailored for vaginal births. Learn more about the structure and function of the female pelvis.

Planned or elective caesarean

There are important things to consider if you are having a planned or elective caesarean such as what happens during and after the procedure.

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• Pregnancy week by week
• Fetal presentation before birth

The way a baby is positioned in the uterus just before birth can have a big effect on labor and delivery. This positioning is called fetal presentation.

Babies twist, stretch and tumble quite a bit during pregnancy. Before labor starts, however, they usually come to rest in a way that allows them to be delivered through the birth canal headfirst. This position is called cephalic presentation. But there are other ways a baby may settle just before labor begins.

Following are some of the possible ways a baby may be positioned at the end of pregnancy.

Head down, face down

When a baby is head down, face down, the medical term for it is the cephalic occiput anterior position. This the most common position for a baby to be born in. With the face down and turned slightly to the side, the smallest part of the baby's head leads the way through the birth canal. It is the easiest way for a baby to be born.

Head down, face up

When a baby is head down, face up, the medical term for it is the cephalic occiput posterior position. In this position, it might be harder for a baby's head to go under the pubic bone during delivery. That can make labor take longer.

Most babies who begin labor in this position eventually turn to be face down. If that doesn't happen, and the second stage of labor is taking a long time, a member of the health care team may reach through the vagina to help the baby turn. This is called manual rotation.

In some cases, a baby can be born in the head-down, face-up position. Use of forceps or a vacuum device to help with delivery is more common when a baby is in this position than in the head-down, face-down position. In some cases, a C-section delivery may be needed.

Frank breech

When a baby's feet or buttocks are in place to come out first during birth, it's called a breech presentation. This happens in about 3% to 4% of babies close to the time of birth. The baby shown below is in a frank breech presentation. That's when the knees aren't bent, and the feet are close to the baby's head. This is the most common type of breech presentation.

If you are more than 36 weeks into your pregnancy and your baby is in a frank breech presentation, your health care professional may try to move the baby into a head-down position. This is done using a procedure called external cephalic version. It involves one or two members of the health care team putting pressure on your belly with their hands to get the baby to roll into a head-down position.

If the procedure isn't successful, or if the baby moves back into a breech position, talk with a member of your health care team about the choices you have for delivery. Most babies in a frank breech position are born by planned C-section.

Complete and incomplete breech

A complete breech presentation, as shown below, is when the baby has both knees bent and both legs pulled close to the body. In an incomplete breech, one or both of the legs are not pulled close to the body, and one or both of the feet or knees are below the baby's buttocks. If a baby is in either of these positions, you might feel kicking in the lower part of your belly.

If you are more than 36 weeks into your pregnancy and your baby is in a complete or incomplete breech presentation, your health care professional may try to move the baby into a head-down position. This is done using a procedure called external cephalic version. It involves one or two members of the health care team putting pressure on your belly with their hands to get the baby to roll into a head-down position.

If the procedure isn't successful, or if the baby moves back into a breech position, talk with a member of your health care team about the choices you have for delivery. Many babies in a complete or incomplete breech position are born by planned C-section.

When a baby is sideways — lying horizontal across the uterus, rather than vertical — it's called a transverse lie. In this position, the baby's back might be:

• Down, with the back facing the birth canal.
• Sideways, with one shoulder pointing toward the birth canal.
• Up, with the hands and feet facing the birth canal.

Although many babies are sideways early in pregnancy, few stay this way when labor begins.

If your baby is in a transverse lie during week 37 of your pregnancy, your health care professional may try to move the baby into a head-down position. This is done using a procedure called external cephalic version. External cephalic version involves one or two members of your health care team putting pressure on your belly with their hands to get the baby to roll into a head-down position.

If the procedure isn't successful, or if the baby moves back into a transverse lie, talk with a member of your health care team about the choices you have for delivery. Many babies who are in a transverse lie are born by C-section.

If you're pregnant with twins and only the twin that's lower in the uterus is head down, as shown below, your health care provider may first deliver that baby vaginally.

Then, in some cases, your health care team may suggest delivering the second twin in the breech position. Or they may try to move the second twin into a head-down position. This is done using a procedure called external cephalic version. External cephalic version involves one or two members of the health care team putting pressure on your belly with their hands to get the baby to roll into a head-down position.

Your health care team may suggest delivery by C-section for the second twin if:

• An attempt to deliver the baby in the breech position is not successful.
• You do not want to try to have the baby delivered vaginally in the breech position.
• An attempt to move the baby into a head-down position is not successful.
• You do not want to try to move the baby to a head-down position.

In some cases, your health care team may advise that you have both twins delivered by C-section. That might happen if the lower twin is not head down, the second twin has low or high birth weight as compared to the first twin, or if preterm labor starts.

• Landon MB, et al., eds. Normal labor and delivery. In: Gabbe's Obstetrics: Normal and Problem Pregnancies. 8th ed. Elsevier; 2021. https://www.clinicalkey.com. Accessed May 19, 2023.
• Holcroft Argani C, et al. Occiput posterior position. https://www.updtodate.com/contents/search. Accessed May 19, 2023.
• Frequently asked questions: If your baby is breech. American College of Obstetricians and Gynecologists https://www.acog.org/womens-health/faqs/if-your-baby-is-breech. Accessed May 22, 2023.
• Hofmeyr GJ. Overview of breech presentation. https://www.updtodate.com/contents/search. Accessed May 22, 2023.
• Strauss RA, et al. Transverse fetal lie. https://www.updtodate.com/contents/search. Accessed May 22, 2023.
• Chasen ST, et al. Twin pregnancy: Labor and delivery. https://www.updtodate.com/contents/search. Accessed May 22, 2023.
• Cohen R, et al. Is vaginal delivery of a breech second twin safe? A comparison between delivery of vertex and non-vertex second twins. The Journal of Maternal-Fetal & Neonatal Medicine. 2021; doi:10.1080/14767058.2021.2005569.
• Marnach ML (expert opinion). Mayo Clinic. May 31, 2023.

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Abnormal Fetal Lie, Presentation, and Position

Hasan, Rabale BS; Bystry, Lisa R. MD; Morosky, Christopher M. MD, MS

Ms. Hasan is a Medical Student, Dr. Bystry is Assistant Professor, and Dr. Morosky is Associate Professor, Department of Obstetrics and Gynecology, UConn Health, 263 Farmington Ave, Farmington, CT 06030; E-mail: [email protected] .

The authors, faculty, and staff in a position to control the content of this CME/CNE activity, and their spouses/life partners (if any), have disclosed that they have no financial relationships with, or financial interests in, any commercial organizations relevant to this educational activity. CME Accreditation Lippincott Continuing Medical Education Institute, Inc., is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.Lippincott Continuing Medical Education Institute, Inc., designates this enduring material for a maximum of 2.0 AMA PRA Category 1 Credits ™. Physicians should claim only the credit commensurate with the extent of their participation in the activity. To earn CME credit, you must read the CME article and complete the quiz and evaluation on the enclosed answer form, answering at least seven of the 10 quiz questions correctly. This CME activity expires on February 27, 2022 . CNE Accreditation Lippincott Professional Development is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's Commission on Accreditation. Lippincott Professional Development will award 1.0 contact hours for this continuing nursing education activity. Instructions for earning ANCC contact hours are included on the test page of the newsletter. This CNE activity expires on December 3, 2021 .

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