Malposition and Malpresentation

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We start off today with some news — for the foreseeable future, CREOGs Over Coffee will move to every-other-week Sunday episodes. It’s been a wild ride and now that we’ve moved across the country from each other, we want to make sure we deliver the same high-quality content we expect and want you to have! While you may hear less of us for now, we’re also working on some other projects, so stay tuned!

On to the episode! And for further reading, check out this review.

Malposition vs. Malpresentation

Fetal lie: the relationship between the fetal long axis and the mother (i.e., longitudinal, transverse, oblique).

Malpresentation: the fetal vertex is not the presenting part, or the part of the fetus closest to the pelvic inlet.

  • Breech: 3-4/100 term pregnancies

  • Face: 1/600-800 term deliveries

  • Brow: 1/500-4000 term deliveries

  • Compound: 1/1500 deliveries

  • Shoulder: 1/200 deliveries

Malposition: the fetus is in vertex position, but the position of the fetal head is not optimal for delivery (i.e., rotated away from an occiput anterior, or OA, position in the pelvis).

  • Occiput transverse (OT) or occiput posterior (OP).

    • These are given a direction based on rotation of the occiput 45 degrees from the direct position (i.e., right occiput posterior denotes rotation of the occiput to maternal right).

      • If occiput < 45 degrees from vertical, is OA or OP.

      • If occiput is > 45 degrees from vertical, is OT.

  • Prior to labor, 15-20% of term fetuses in cephalic presentation are in OP position. At delivery, only 5% will persist this way, as they will often rotate spontaneously.

Action to take with various malpositions and malpresentations:

First, a word on “normal” vaginal deliveries 

  • In OA position, the neck flexes to bring the chin to the chest → smaller diameter of the fetal head (about 9.5 cm), which is usually able to traverse the obstetric conjugate (average 10.5cm), which is the shortest anteroposterior pelvic diameter.

    • In other positions (ie. face or brow), the neck is extended and there is larger fetal cephalic head diameter that needs to traverse this area, making it more difficult to pass.

Breech, Transverse Lie, & Shoulder Presenations

  • We have previously discussed breech vaginal delivery, but current recommendation for breech and shoulder presentation is cesarean section.

  • Shoulder presentations cannot deliver vaginally. The shoulder is wedged into the pelvis, and the head will lie in one of the iliac fossa, and the breech in the other - the baby becomes wedged into the pelvic inlet and cannot get past.

  • For shoulder, describe using location of the scapula: 

    • Left scapula anterior (LSA), and RSA. 

    • Left scapula posterior (LSP), and RSP. 

  • With transverse lies, just like breech, can offer ECV prior to labor, but once labor occurs, usually versions become very difficult to do.

Face Presentation

  • The fetal face from forehead to chin is the leading fetal body part descending into the birth canal. This is usually diagnosed by vaginal exam (can palpate the orbital ridge, nose, mouth, chin), not able to palpate the fontanelles.

  • Described using location of the chin, or mentum.

    • At diagnosis, about 60% are mentum anterior and 26% are mentum posterior (ie. chin up or chin down); 15% are mentum transverse.

  • Management varies depending on presentation:

    • Mentum anterior The fetal chin needs to pass under the symphysis pubis, and fetal neck may need to extend even more (though it is already extended).

      • After the chin clears the symphysis, it is possible for vaginal delivery, and women should be allowed to push during second stage.

      • Forceps can be used, but engagement doesn’t occur until the face is at +2 station, and the chin, rather than the occiput becomes the focal point for orientation.

      • Vacuums are contraindicated… because where would you put it?!?!

    • Mentum posterior In this case, the fetal neck is maximally extended and cannot extend further to allow the occiput to pass under the symphysis.

      • Will NOT deliver vaginally unless there is spontaneous rotation to mentum anterior. 

      • If discovered early in labor, can have expectant management in the hopes that the mentum will spontaneously rotate to anterior.

      • However, recommendation is for cesarean if persistent mentum posterior with abnormal labor progress.

      • What about attempting rotation? 

        • Not a lot of cases, and there have been case reports of successful internal and external manipulation.

        • Some case reports of uterine rupture, cord prolapse, and cervical spine trauma.

        • Overall: if cesarean is available, would favor cesarean.

Brow presentation

  • A variant of face presentation, when presenting part is the anterior fontanelle to the brow (orbital ridge), which does not include the mouth and chin.

  • Diagnosis is usually made with vaginal exam (you can feel the forehead, orbits, and nose).

  • Management:

    • Can undergo trial of labor, as brow presentation may be transitional 

      • In one study, when brow presentation was diagnosed early, 67-75% of fetuses spontaneously converted to a more favorable presentation and delivered vaginally.

      • If diagnosed later:

        • 50% spontaneously converted and delivered;

        • 30% the neck extended further;

        • 20% the neck flexed and resulted in occiput posterior presentation. 

    • Rotational maneuvers, vacuum, and forceps are not recommended. 

Persistent occiput posterior 

  • Most common malposition, encountered very frequently in clinical practice, and will often convert spontaneously.

  • Manage expectantly in first stage of labor. In second stage of labor can also be expectant as long as fetal heart rate is reassuring and labor is progressing 

    • 50-80% of OP fetuses at beginning of second stage will rotate spontaneously to OA. 

    • If clinically adequate pelvis with a prolonged second stage - can attempt manual rotation to the OA position.

    • Prospective study - manual rotation vs. Expectant management of OP demonstrated higher likelihood of vaginal delivery and fewer cases of persistent OP presentation.

  • Manual rotation techniques 

    • Digital - placing tips of index and middle fingers in the anterior segment of the lamboid suture near the posterior fontanelle, and then used to flex and slightly dislodge the head, and rotation to OA position with the operator’s hand and forearm.

    • Hand - placing operator’s four fingers behind the posterior parietal bone with palm up and thumb over the anterior parietal bone. Right hand for LOP, left hand for ROP.

      • Flex and slightly dislodge the head → rotate.