Fetal Malpresentation and Malposition

Fetal presentation describes which part of the fetus will enter through the cervix first, while position is the orientation of the fetus compared to the maternal bony pelvis. Presentations include vertex (the fetal occiput will present through the cervix first), face, brow, shoulder, and breech. If a fetal limb is presenting next to the presenting part (e.g., the hand is next to the head), this is known as a compound presentation. Malpresentation refers to any presentation other than vertex, with the most common being breech presentations. Vaginal delivery of a breech infant increases the risk for head entrapment and hypoxia, so, especially in the United States, mothers are generally offered a procedure to help manually rotate the baby to a head-down position instead (known as an external cephalic version) or a planned cesarean delivery.

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Overview

Definition

  • The “presenting part” refers to the part of the baby that will come through the cervix first. 
  • The position refers to how that body part (and thus the baby) is oriented within the maternal pelvis. 
  • The uterine fundus is typically roomier, so babies tend to orient themselves head down so that their body and limbs occupy the larger portion of the uterus.

Clinical relevance

  • The maternal pelvis has a diameter of about 10 cm, through which the fetus must pass.
  • The presentation and position of the fetus will determine how wide the fetus is (known as the “presenting fetal diameter”) as it attempts to pass through the maternal pelvis.
  • Certain presentation/positions are more difficult (or even impossible) to pass through the pelvis because of their large presenting diameter.
  • Knowledge of the presentation and position are required to safely manage labor and delivery.

Risk factors for fetal malpresentation

  • Multiparity (which can result in lax abdominal walls)
  • Multiple gestations (e.g., twins)
  • Prematurity
  • Uterine abnormalities (e.g., leiomyomas, uterine septa)
  • Narrow pelvis shapes
  • Fetal anomalies (e.g., hydrocephalus)
  • Placental anomalies (e.g., placenta previa, in which the placenta covers the internal cervical os)
  • Amniotic fluid abnormalities: 
    • Polyhydramnios (too much fluid)
    • Oligohydramnios (not enough fluid)
  • Malpresentation in a previous pregnancy

Epidemiology

Prevalence rates for different malpresentations at term:

  • Vertex presentation, occiput posterior position: 1 in 19 deliveries
  • Breech presentation: 1 in 33 deliveries
  • Face presentation: 1 in 600–800 deliveries
  • Transverse lie: 1 in 833 deliveries
  • Compound presentation: 1 in 1500 deliveries 

Fetal Lie and Presentation

Fetal lie

Fetal lie is how the long axis of the fetus is oriented in relation to the mother. Possible lies include:

  • Longitudinal: fetus and mother have the same vertical axis (their spines are parallel).
  • Transverse: fetal vertical axis is at a 90-degree angle to mother’s vertical axis (their spines are perpendicular).
  • Oblique: fetal vertical axis is at a 45-degree angle to mother’s vertical axis (unstable, and will resolve to longitudinal or transverse during labor).

Presentation

Presentation describes which body part of the fetus will pass through the cervix first. Presentations include:

  • Longitudinal presentations:
    • Cephalic: head down
    • Breech: bottom/feet down
  • Transverse presentation: shoulder 
  • Compound presentation: an extremity presents alongside the primary presenting part

Cephalic presentations

Cephalic presentations can be categorized as:

  • Vertex presentation: chin flexed, with the occipital fontanel as the presenting part
  • Face presentation
  • Brow presentation: forehead is the presenting part

Breech presentations

Breech presentations can be categorized as:

  • Frank breech: bottom down, legs extended (50%–70%) 
  • Complete breech: bottom down, hips and knees both flexed
  • Incomplete breech: 1 or both hips not completely flexed
  • Footling breech: feet down
Breech presentations

Frank, complete, and footling breech presentations

Image by Lecturio. License: CC BY-NC-SA 4.0

Transverse and compound presentations

  • Transverse presentations: 
    • Uncommon, but when they occur, the presenting fetal part is the shoulder.
    • If the cervix begins dilating, the arm may prolapse through the cervix.
  • In compound presentations, the most common situation is a hand or arm presenting with the head.

Fetal malpresentation

  • Any presentation other than vertex
  • Clinically, this means breech, face, brow, and shoulder presentations.

Position

Position describes the relation of the fetal presenting part to the maternal bony pelvis.

Vertex positions

Positions for vertex presentations describe the position of the fetal occiput.

  • Identified on cervical exam as the area in the midline between the anterior and posterior fontanelles
  • The fetal occiput is classified as being:
    • Anterior, posterior, or transverse in relation to the maternal pelvis
    • Being on the maternal right or left
  • Terminology examples:
    • Right or left occiput anterior
    • Right or left occiput posterior
    • Right or left occiput transverse
    • Direct occiput anterior or posterior
  • The most common positions (and easiest for vaginal delivery) are occiput anterior.
Vertex positions

Overview of different vertex positions
LOA: left occiput anterior
LOP: left occiput posterior
LOT: left occiput transverse
OA occiput anterior
OP: occiput posterior
ROA: right occiput anterior
ROP: right occiput posterior
ROT: right occiput transverse

Image by Lecturio. License: CC BY-NC-SA 4.0

Face and brow positions

Positions for face and brow presentations describe the position of the chin.

  • The chin is referred to as the mentum.
  • Like occiput positions, mentum positions include:
    • Right or left mentum anterior
    • Right or left mentum posterior
    • Right or left mentum transverse
    • Direct mentum anterior or posterior

Breech and shoulder positions

  • Positions for breech presentations describe the position of the sacrum. Similar to other presentations, they include anterior, posterior, and transverse and right, left, and direct.
  • Positions for shoulder presentations/transverse lies describe the position of the back; they are simply described as:
    • Dorso-superior (back up)
    • Dorso-inferior (back down)

Attitude and asynclitism

  • Attitude: amount of flexion or extension of the fetal head
  • Asynclitism: 
    • Lateral deflection of the sagittal suture to 1 side or the other
    • Mild degrees of asynclitism are normal.
    • More severe asynclitism increases the presenting fetal diameter and makes it more difficult for the fetal head to pass through the maternal pelvis.

Fetal malposition

  • Commonly refers to any position other than right occiput anterior, left occiput anterior, or direct occiput anterior
  • All nonvertex presentations are also malpositioned.
  • The terms fetal malpresentation and fetal malposition are often used interchangeably.

Presenting Diameter

  • The presenting diameter refers to the width of the presenting part.
  • The maternal pelvis is about 10 cm at its narrowest point; the infant must orient itself so that it can fit through.
  • Most commonly, the infant will move into a cephalic, vertex presentation, in 1 of the occiput anterior positions → presents the narrowest diameter
  • Presenting diameters:
    • Vertex presentation: suboccipitobregmatic diameter, approximately 9.5 cm
    • Vertex presentation with deflexed head: occipitofrontal diameter, approximately 11.5 cm
    • Brow presentation: occipitomental diameter, approximately 13 cm
    • Face presentation: submentobregmatic diameter, approximately 9.5 cm

Diagnosis

How to establish lie, presentation, and position

Delivery is managed differently depending on the presentation and position of the infant. This information can be established in several different ways:

  • Leopold’s maneuvers
  • Ultrasonography
  • Cervical examination

Leopold’s maneuvers

  • Techniques using abdominal palpation to determine the presentation of the fetus
  • Techniques/maneuvers:
    • Palpate the uterine fundus and suprapubic area to determine the lie/presentation: 
      • The fetal head will be hard and round.
      • The lower body will be bulkier, nodular, and mobile.
    • Palpate the sides of the maternal abdomen to determine the orientation: 
      • The back will be hard and smooth.
      • The other side (anterior surface of the fetus) will be filled with irregular, mobile fetal parts.
  • Experienced providers can also estimate the fetal weight using these maneuvers.

Ultrasonography

  • Bedside abdominal ultrasonography can easily identify the fetal head and its orientation.
  • Quick bedside ultrasonography on admission to labor and delivery to assess fetal presentation is considered standard of care.
  • Findings:
    • The fetal head will typically encompass the entire window and appear like a large white circle (the fetal skull).
    • Identification of the eyes can help determine position.
  • While it is good clinical practice to “lay hands” on the mother using Leopold’s maneuvers, bedside ultrasonography should always be performed, if available, to confirm findings because:
    • It is quick and easy to perform and presents minimal risk to mother and infant.
    • Allowing mothers to labor with infants in a noncephalic presentation significantly increases the risks to both of them.
Suprapubic bedside ultrasound confirming a cephalic presentation

Suprapubic bedside ultrasound showing the large white circle of the fetal skull, confirming a cephalic presentation
F: fetal falx

Image: “ Prenatal ultrasound scans image of the fetus” by Wijerathne BT, Rathnayake GK, Ranaraja SK. License: CC BY 3.0

Vaginal and cervical examination

  • As the cervix dilates, the fetal fontanelles can be directly palpated.
  • Identifying the location of the fetal fontanelles allows the practitioner to establish the position.
  • Technique: 
    • Insert 1–2 fingers through the cervix posteriorly.
    • Sweep fingers along the fetal head moving anteriorly.
    • This maneuver allows for identification of the sagittal suture.
    • The fontanelles are then identified by moving along the sagittal suture.

Management of Cephalic and Compound Presentations

Vertex presentations

  • Expectant management
  • All have high chances of successful vaginal delivery.

Compound presentations

  • Management: 
    • Observation when labor is progressing normally (many compound presentations will resolve spontaneously intrapartum).
    • Can attempt to gently pinch the compound extremity trying to provoke the fetus into withdrawing the part (no good quality evidence, but unlikely to be harmful)
    • Can attempt to manually replace the compound extremity
    • If labor is prolonged and the compound part remains, cesarean delivery (CD) should be performed.
  • Complications:
    • Prolonged labor
    • Umbilical cord prolapse
    • Increased maternal morbidity from lacerations
    • Ischemia of the compound part

Brow presentations

  • The majority spontaneously convert to a vertex presentation.
  • Expectant management
  • Cesarean delivery may be required if labor is prolonged.

Face presentations

  • Management depends on the position.
  • Mentum anterior (chin facing the maternal pubic bone): 
    • Expectant management
    • Can be delivered vaginally by an experienced provider
    • Cesarean delivery may be required.
  • Mentum posterior (MP; chin facing the maternal sacrum):
    • Head is fully extended and unable to pass through the birth canal.
    • Normally, the fetal head flexes as it passes under the pubic bone; however, this is impossible in an MP position.
    • Cesarean delivery is always required (unless the infant spontaneously rotates to a mentum anterior (MA) position).

Risks and Management of Breech and Transverse Presentations

There are 3 primary options for managing breech presentations: performing CD, attempting an external cephalic version to manually rotate the baby into a vertex presentation for attempted vaginal delivery, or a planned vaginal breech delivery (which is generally not done in the United States).

Natural history of breech presentations

Most infants will spontaneously rotate to a vertex presentation as the pregnancy progresses. At different gestational ages, the prevalence of breech presentations is:

  • < 28 weeks: 20%–25%
  • 32 weeks: 10%–15%
  • Term (> 37 weeks): 3% 
  • Spontaneous version is possible even at > 40 weeks.
  • Factors that ↑ chance of spontaneous version:
    • Flexed fetal legs
    • Polyhydramnios
    • Longer umbilical cord
    • Lack of fetal/uterine anomalies
    • Multiparity

Fetal risks associated with breech presentations

The following risks are associated with breech presentations in utero, regardless of mode of delivery:

  • ↑ Association with congenital malformations
  • Torticollis
  • Developmental hip dysplasia 

Fetal risks associated with vaginal breech delivery

The primary risk of a vaginal breech delivery is fetal head entrapment:

  • The fetal body delivers, but the head remains trapped in the uterus.
  • Causes compression of the umbilical cord running past the head (between the delivered umbilicus and the undelivered placenta) 
  • Leads to hypoxia until head is delivered → ↑ risk of fetal death
  • Occurs because the fetal head is the largest part of the fetus and thus the most difficult to squeeze beneath the pubic bone:
    • The cervix may not be fully dilated enough to accommodate the head.
    • The fetal head may not fit through the bony pelvis.
    • The mother’s expulsive efforts are unable to quickly deliver the head.
  • Other risks of vaginal breech delivery:
    • Umbilical cord prolapse during labor → requires emergent CD
    • Birth injuries to the fetus (e.g., brachial plexus injury)

Vaginal breech delivery

Vaginal breech deliveries for singleton gestations may be considered for certain low-risk women if vaginal delivery is strongly desired by the mother. In contrast, vaginal breech deliveries are done frequently for breech 2nd twins; the procedure is known as a breech extraction.

  • Mothers must be fully counseled on risks.
  • Mothers and infants should be monitored throughout labor with continuous electronic fetal heart rate (FHR) and tocometry monitors.
  • Mothers should understand that a CD will be recommended if there are signs of fetal distress or prolonged labor.
  • Avoid artificial rupture of membranes to ↓ risk of cord prolapse.
  • Criteria for selecting low-risk women for planned vaginal breech delivery:
    • Frank or complete breech presentation with no hyperextension of the fetal head on ultrasonography
    • No contraindications to a vaginal birth
    • No prior CDs
    • Prior successful vaginal deliveries (i.e., multiparity)
    • Gestational age ≥ 36 weeks
    • Spontaneous labor
    • Normal bony pelvis shown on X-ray
    • Estimated fetal weight between approximately 2500 and 3500 grams (exact range varies based on clinician)
  • Breech extraction of a 2nd twin:
    • Immediately after delivery of the 1st twin in the cephalic presentation, the physician reaches up into the uterus, manually grabs the infant’s legs, and gently guides them down through the birth canal while the cervix is still fully dilated.
    • ↓ Risk of head entrapment compared to singleton vaginal breech deliveries

External cephalic version

An external cephalic version (ECV) is a procedure in which the physician attempts to manually rotate the fetus from a breech to a cephalic presentation by pushing on the maternal abdomen.

  • Success rate: 
    • Approximately 50%–60% (higher in multiparous than in nulliparous women) 
    • In 1 large study, after a successful version:
      • 97% of infants remained cephalic at birth.
      • 86% delivered vaginally.
  • Plan:
    • Women who are candidates for ECV should be counseled on their options to attempt an ECV, or they may simply elect to schedule a CD.
    • Typically done at 37 weeks (balances risks and benefits):
      • Infant is full term in case emergent CD is required because of complications from the procedure (e.g., placental abruption).
      • Better ratio of infant size to fluid level than later in pregnancy
      • Allows infant more time for spontaneous version than if the procedure was done earlier
    • After a successful version, the mother can await spontaneous labor or be induced immediately, depending on the situation.
    • After an unsuccessful version, the mother typically is scheduled for a planned CD at 39 weeks. 
      • There is still a chance that the infant may spontaneously rotate between the failed ECV and the planned CD date; therefore, presentation should always be checked immediately prior to CD.
  • Contraindications for ECV:
    • Another contraindication for a vaginal delivery (e.g., placenta previa)
    • Severe oligohydramnios
    • Nonreassuring fetal monitoring prior to the procedure
    • A hyperextended fetal head
    • Significant fetal or uterine anomalies
    • Multiple gestations (e.g., twins)
  • Risks:
    • Placental abruption: the pressure placed on the uterus during the procedure can result in premature separation of the placenta from the uterus:
      • Leads to fetal and maternal hemorrhage
      • An immediate CD is required.
    • Premature rupture of membranes (PROM): the pressure placed on the uterus during the procedure can result in rupture of membranes:
      • If the version was successful, labor should be induced immediately.
      • If the version was unsuccessful, the mother should undergo immediate CD.
      • Cord prolapse: can occur with PROM and requires immediate/emergent CD.
    • Fetal distress: 
      • Common during the procedure, but typically resolves shortly after pressure on the abdomen is released.
      • If distress persists, the mother should undergo an immediate CD.

Cesarean delivery

  • Scheduled at 39 weeks’ gestational age (WGA) if the infant is known to be in the breech presentation.
  • Alternative option to attempting ECV
  • Compared to a vaginal delivery of a cephalic infant, CD has a higher risk for:
    • Postpartum hemorrhage
    • Postpartum endomyometritis
    • Maternal injury
    • Longer recovery time postpartum
    • Complications in future pregnancies (e.g., placenta previa, placenta accreta, uterine rupture)
  • Indications for CD with breech presentations:
    • Maternal request (mother declines ECV attempt)
    • ECV contraindicated
    • ECV unsuccessful
    • Fetal distress during labor
    • Prolonged labor

Management of transverse presentations

  • As with breech presentations, mothers may be offered an attempt at ECV or a CD.
  • Unlike breech presentations, vaginal transverse delivery is always contraindicated.

References

  1. Hofmeyr, G.J. (2021). Overview of breech presentation. In Barss, V.A. (Ed.), UpToDate. Retrieved July 14, 2021, from https://www.uptodate.com/contents/overview-of-breech-presentation 
  2. Hofmeyr, G.J. (2021). Delivery of the singleton fetus in breech presentation. In Barss, V.A. (Ed.), UpToDate. Retrieved July 14, 2021, from https://www.uptodate.com/contents/delivery-of-the-singleton-fetus-in-breech-presentation 
  3. Hofmeyr, G.J. (2021). External cephalic version. In Barss, V.A. (Ed.), UpToDate. Retrieved July 14, 2021, from https://www.uptodate.com/contents/external-cephalic-version 
  4. Julien, S., and Galerneau, F. (2021). Face and brow presentations in labor. In Barss, V.A., (Ed.), UpToDate. Retrieved July 14, 2021, from https://www.uptodate.com/contents/face-and-brow-presentations-in-labor 
  5. Strauss, R.A., Herrera, C.A. (2021). Transverse fetal lie. In Barss, V.A., (Ed.), UpToDate. Retrieved July 14, 2021, from https://www.uptodate.com/contents/transverse-fetal-lie 
  6. Barth, W.H. (2021). Compound fetal presentation. In Barss, V.A., (Ed.), UpToDate. Retrieved July 14, 2021, from https://www.uptodate.com/contents/compound-fetal-presentation 
  7. Cunningham, F. G., Leveno, K. J., et al. (2010). Williams Obstetrics, 23rd ed., pp. 374‒382. 

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