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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, forceps delivery, or cesarean section.
Fetal dystocia may occur when the fetus is too large for the pelvic opening (fetopelvic disproportion) or is abnormally positioned (eg, breech presentation, shoulder dystocia). 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 fetal weight is < 4500 g (in women without diabetes) and augmentation of labor restores normal progress, labor can safely continue. If progress is slow in the 2nd stage of labor, women are evaluated to determine whether 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 and thus a larger diameter of the head must pass through the pelvis. In face presentation, the head is hyperextended, and the chin may be posterior. Brow presentation usually converts spontaneously to occiput or face presentation. Many occiput posterior presentations require forceps delivery or cesarean section. If the chin is posterior in face presentation, cesarean section is necessary.
Breech
presentation:
The 2nd most common abnormal presentation is breech (buttocks before the head). In frank breech, the fetal hips are flexed, and the knees extended. In complete breech, the fetus seems to be sitting with hips and knees flexed. In 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 to be trapped during delivery, often compressing the umbilical cord.
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. Breech presentation also increases risk of preterm delivery, fetal brachial plexus or spinal cord birth trauma, and perinatal death. Preventing complications is more effective and easier than treating them, so abnormal presentation must be identified before delivery. Cesarean section is usually done, although the external version maneuver can sometimes move the fetus to vertex presentation before labor, usually at 37 or 38 wk. The external version maneuver usually involves gently pressing on the maternal abdomen. A dose of a short-acting tocolytic ( terbutaline 0.25 mg sc) may help. The success rate is about 50 to 60%.
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 section 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. Risk factors include a large fetus and maternal obesity or diabetes mellitus. Shoulder dystocia is identified if the head, after passing through the cervix, appears to be pulled back tightly against the vulva (turtle sign). Asphyxiation can occur because the vaginal canal compresses the chest so that the fetus cannot breathe. Hypoxic injury can begin within 4 to 5 min.
Extra personnel are summoned to the room, and various maneuvers are tried sequentially, if needed, to disengage the anterior shoulder. (1) 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. (2) 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). (3) The posterior shoulder is pushed up toward the sacrum, and the obstetrician inserts a hand to flex the infant's elbow, grasps the infant's hand, and pulls it outside to deliver the infant's entire posterior arm. If all maneuvers are ineffective, the infant's head is flexed and pushed back into the vagina, and the infant is then delivered by cesarean section (Zavanelli maneuver).
Last full review/revision November 2005
Content last modified November 2005
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