Abnormal fetal lie or presentation may occur due to fetal size, fetal anomalies, uterine structural abnormalities, multiple gestation, or other factors. Diagnosis is by examination or ultrasonography. Management is with physical maneuvers to reposition the fetus, operative vaginal delivery, or cesarean delivery.
Terms that describe the fetus in relation to the uterus, cervix, and maternal pelvis are
Fetal presentation: Fetal part that overlies the maternal pelvic inlet; vertex (cephalic), face, brow, breech, shoulder, funic (umbilical cord), or compound (more than one part, eg, shoulder and hand)
Fetal position: Relation of the presenting part to an anatomic axis; for transverse presentation, occiput anterior, occiput posterior, occiput transverse
Fetal lie: Relation of the fetus to the long axis of the uterus; longitudinal, oblique, or transverse
Normal fetal lie is longitudinal, normal presentation is vertex, and occiput anterior is the most common position.
Abnormal fetal lie, presentation, or position may occur with
Fetopelvic disproportion (fetus too large for the pelvic inlet)
Fetal congenital anomalies
Uterine structural abnormalities (eg, fibroids, synechiae)
Multiple gestation
Several common types of abnormal lie or presentation are discussed here.
Transverse lie
Fetal position is transverse, with the fetal long axis oblique or perpendicular rather than parallel to the maternal long axis. Transverse lie is often accompanied by shoulder presentation, which requires cesarean delivery.
Breech presentation
There are several types of breech presentation.
Frank breech: The fetal hips are flexed, and the knees extended (pike position).
Complete breech: The fetus seems to be sitting with hips and knees flexed.
Single or double footling presentation: One or both legs are completely extended and present before the buttocks.
Types of breech presentations
Breech presentation makes delivery difficult ,primarily because the presenting part is a poor dilating wedge. Having a poor dilating wedge can lead to incomplete cervical dilation, because the presenting part is narrower than the head that follows. The head, which is the part with the largest diameter, can then be trapped during delivery.
Additionally, the trapped fetal head can compress the umbilical cord if the fetal umbilicus is visible at the introitus, particularly in primiparas whose pelvic tissues have not been dilated by previous deliveries. Umbilical cord compression may cause fetal hypoxemia.
Predisposing factors for breech presentation include
Uterine abnormalities
Fetal anomalies
If delivery is vaginal, breech presentation may increase risk of
Umbilical cord prolapse
Perinatal death
Face or brow presentation
In face presentation, the head is hyperextended, and position is designated by the position of the chin (mentum). When the chin is posterior, the head is less likely to rotate and less likely to deliver vaginally, necessitating cesarean delivery.
Brow presentation usually converts spontaneously to vertex or face presentation.
Occiput posterior position
The most common abnormal position is occiput posterior.
The fetal neck is usually somewhat deflexed; thus, a larger diameter of the head must pass through the pelvis.
Progress may arrest in the second phase of labor. Operative vaginal delivery or cesarean delivery is often required.
Position and Presentation of the Fetus
Toward the end of pregnancy, the fetus moves into position for delivery. Normally, the presentation is vertex (head first), and the position is occiput anterior (facing toward the pregnant patient's spine) with the face and body angled to one side and the neck flexed. Abnormal presentations include face, brow, breech, and shoulder. Occiput posterior position (facing toward the pregnant patient's pubic bone) is less common than occiput anterior position. |
Key Points
If a fetus is in the occiput posterior position, operative vaginal delivery or cesarean delivery is often required.
In breech presentation, the presenting part is a poor dilating wedge, which can cause the head to be trapped during delivery, often compressing the umbilical cord.
For breech presentation, usually do cesarean delivery at 39 weeks or during labor, but external cephalic version is sometimes successful before labor, usually at 37 or 38 weeks.
