Fetal dystocia may occur when the fetus is
Too large for the pelvic opening (fetopelvic disproportion)
Abnormally positioned (eg, breech presentation)
Treatment depends on the reason for the fetal dystocia.
Normal fetal presentation is vertex, with the occiput anterior.
Diagnosis of fetopelvic disproportion is suggested by prenatal clinical estimates of pelvic dimensions Physical Examination Ideally, women who are planning to become pregnant should see a physician before conception; then they can learn about pregnancy risks and ways to reduce risks. As part of preconception care... read more , ultrasonography, and protracted labor.
If augmentation of labor restores normal progress and fetal weight is < 5000 g in women without diabetes or < 4500 g in women with diabetes, labor can safely continue.
If progress is slower than expected in the 2nd stage of labor, women are evaluated to determine whether operative vaginal delivery Operative Vaginal Delivery Operative vaginal delivery involves application of forceps or a vacuum extractor to the fetal head to assist during the 2nd stage of labor and facilitate delivery. Indications for forceps delivery... read more (by forceps or vacuum extractor) is safe and appropriate. Trying to deliver a fetus that is too large using forceps or a vacuum extractor can cause problems.
Occiput posterior presentation
The most common abnormal presentation is occiput posterior.
The fetal neck is usually somewhat deflexed; thus, a larger diameter of the head must pass through the pelvis.
Many occiput posterior presentations require operative vaginal delivery or cesarean delivery Cesarean Delivery Cesarean delivery is surgical delivery by incision into the uterus. Up to 30% of deliveries in the US are cesarean. The rate of cesarean delivery fluctuates. It has recently increased, partly... read more .
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.
The 2nd most common abnormal presentation is breech (buttocks before the head). There are several types:
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.
Breech presentation is a problem primarily because the presenting part is a poor dilating wedge, which can cause the head, which follows, to be trapped during delivery, often compressing the umbilical cord.
Umbilical cord compression may cause fetal hypoxemia. The 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.
Predisposing factors for breech presentation include
If delivery is vaginal, breech presentation may increase risk of
Dystocia (difficult delivery)
Preventing complications is more effective and easier than treating them, so abnormal presentation must be identified before delivery. Cesarean delivery is usually done at 39 weeks or when the woman presents in labor, although external cephalic version can sometimes move the fetus to vertex presentation before labor, usually at 37 or 38 weeks. This technique involves gently pressing on the maternal abdomen to reposition the fetus. A dose of a short-acting tocolytic (terbutaline 0.25 mg subcutaneously) may help some women. The success rate is about 50 to 75%.
Fetal position is transverse, with the fetal long axis oblique or perpendicular rather than parallel to the maternal long axis. Shoulder-first presentation requires cesarean delivery unless the fetus is a 2nd twin.
Position and Presentation of the Fetus
Toward the end of pregnancy, the fetus moves into position for delivery. Normally, the position of a fetus is facing rearward (toward the woman’s back) with the face and body angled to one side and the neck flexed, and presentation is head first.
An abnormal position is facing forward, and abnormal presentations include face, brow, breech, and shoulder.
In this infrequent condition, presentation is vertex, but the anterior fetal shoulder becomes lodged behind the symphysis pubis after delivery of the fetal head, preventing vaginal delivery. Shoulder dystocia is recognized when the fetal head is delivered onto the perineum but appears to be pulled back tightly against the perineum (turtle sign).
Risk factors include
Shoulder dystocia in a previous pregnancy
Risk of neonatal morbidity (eg, brachial plexus injury, bone fractures) and mortality is increased. Maternal morbidity may include postpartum hemorrhage, perineal lacerations, sphincter injuries, symphysis pubis separation, and lateral femoral cutaneous neuropathy associated with hyperflexion of the legs.
Once shoulder dystocia is recognized, extra personnel are summoned to the room, and various maneuvers are tried sequentially to disengage the anterior shoulder:
The woman’s thighs are hyperflexed to widen the pelvic outlet (McRoberts maneuver), and suprapubic pressure is applied to rotate and dislodge the anterior shoulder. Fundal pressure is avoided because it may worsen the condition or cause uterine rupture.
The obstetrician inserts a hand into the posterior vagina and presses the posterior or anterior shoulder to rotate the fetus in whichever direction is easier (Wood screw maneuver or Rubin maneuver).
The obstetrician inserts a hand, flexes the posterior elbow, and sweeps the arm and hand across the fetal chest to deliver the infant’s entire posterior arm.
These maneuvers increase risk of fracture of the humerus or clavicle. Sometimes the clavicle is intentionally fractured in a direction away from fetal lung to disengage the shoulder. An episiotomy can be done at any time to facilitate the maneuvers.
If all maneuvers are ineffective, the obstetrician flexes the infant’s head and reverses the cardinal movements of labor, replacing the fetal head back into the vagina or uterus (Zavanelli maneuver); the infant is then delivered by cesarean.
If fetopelvic disproportion causes labor to progress more slowly than expected in the 2nd stage of labor, evaluate women to determine whether operative vaginal delivery is safe and appropriate.
Many occiput posterior presentations require operative vaginal delivery or cesarean delivery.
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.
Once shoulder dystocia is recognized, summon extra personnel to the room, and try various maneuvers sequentially to disengage the anterior shoulder; if these maneuvers are unsuccessful, replace the fetal head back into the vagina or uterus and deliver the infant by cesarean.