Buy the Book PDA Download

Update Me E-mail alerts The Merck Manual Minute

Print This Topic Email This Topic

Fetal dystocia is abnormal fetal size or position resulting in difficult delivery. Diagnosis is by examination, ultrasonography, or response to augmentation of labor. Treatment is with physical maneuvers to reposition the fetus, operative vaginal delivery, or cesarean delivery.

Fetal dystocia may occur when the fetus is too large for the pelvic opening (fetopelvic disproportion) or is abnormally positioned (eg, breech presentation). Normal fetal presentation is vertex, with the occiput anterior.

Fetopelvic disproportion: Diagnosis is suggested by prenatal clinical estimates of pelvic dimensions (see Approach to the Pregnant Woman and Prenatal Care: Physical Examination), 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 (by forceps or vacuum extractor) is safe and appropriate.

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.

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 occiput or face presentation.

Breech 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.

Umbilical cord compression may cause fetal hypoxemia. The fetal head is probably compressing 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 premature labor, uterine abnormalities, and fetal anomalies. If delivery is vaginal, breech presentation may increase risk of birth trauma, dystocia, and perinatal death. 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 wk or when the patient presents in labor, although external cephalic version can sometimes move the fetus to vertex presentation before labor, usually at 37 or 38 wk. This technique involves gently pressing on the maternal abdomen to reposition the fetus. A dose of a short-acting tocolytic ( terbutaline Some Trade Names
BRETHINE
BRICANYL
Click for Drug Monograph
0.25 mg sc) may help. The success rate is about 50 to 75%.

Transverse lie: 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.

Shoulder dystocia: In this infrequent condition, presentation is vertex, but the anterior fetal shoulder is lodged behind the symphysis pubis, 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 a large fetus, maternal obesity, diabetes mellitus, prior shoulder dystocia, operative vaginal delivery, and prolonged labor. Risk of neonatal morbidity (eg, brachial plexus injury, bony fractures) and mortality is increased

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 (McRobert's 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 shoulder to rotate the fetus in whichever direction is easier (Wood's screw 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.

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; the infant is then delivered by cesarean section (Zavanelli maneuver).

Last full review/revision December 2008 by Julie S. Moldenhauer, MD

Content last modified December 2008