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Hospital lacks the ability to perform emergency cesarean around the clock: The general hospital population has about the same potential for a labor emergency as the potential for the scar giving way. If the hospital isn’t safe for a VBAC labor, then it isn’t safe for any woman to labor there.
Prior cesarean for poor progress: also known as “failure to progress,” “labor dystocia,” “cephalopelvic disproportion”: Eighteen studies report the VBAC rate when the first cesarean was performed for one of these reasons (15). All but two found that half or more of the group gave birth vaginally. Half the studies report rates between 60 and 69 percent, so your odds of vaginal birth with a supportive practitioner should be roughly two out of three.
Suspected large baby: Ultrasound scans predicting weights over 8 lbs. 13 oz. (4,000 grams) will be wrong one-third to one-half of the time (15). Even when babies weigh more than 4,000 grams, the VBAC rate is about two out of three (30).
Type of uterine scar not known: Unless the prior cesarean was done in Latin America or certain other countries or for the reasons listed, the odds are 99 to 1 the scar is transverse (10).
Low vertical uterine scar: Doctors perform a low vertical incision for cesarean deliveries of premature babies because the lower part of the uterus isn’t well enough developed yet for a transverse incision. Data suggest this scar is as strong as a transverse scar (24,33).
More than one prior cesarean: Two studies reported rates of less than 2 percent and less than 1 percent (3,25),. A third said merely that the rate did not differ from the rate with one uterine scar (9). Overall, the chances of vaginal birth were two out of three.
Twins: We haven’t much data on twins, but VBAC doesn’t seem to pose excess risk (11,25,27,35).
Breech: External cephalic version is a procedure in which the doctor turns the baby head down in late pregnancy by manipulating the woman’s belly. What little data we have suggests this procedure is safe in women with prior cesareans (8,19,32).
Labor induction is indicated: Large studies show that straight oxytocin (Pitocin) induction increases the incidence of symptomatic scar separation only slightly from 4 to 5 per 1,000 to 7 to 8 per 1,000 (21,30). The risk comes when prostaglandins are used. Prostaglandin E2 (dinoprostone), the type found in Prepidil and Cervidil, increases the incidence of the scar giving way to 25 per 1,000 (21). Prostaglandin E1 (misoprostol), the type found in Cytotec, raises it even higher, possibly much higher (12). Some evidence suggests that long, unproductive oxytocin inductions may also be a problem (20).
In any case, induction should be reserved for those situations where the risks of awaiting labor outweigh the risks of inducing it. This occurs far less often than the typical obstetrician thinks it does. One of the common reasons for induction is questionable: induction at 41 weeks. Others aren’t supported by the research at all: convenience inductions, induction for suspected big baby, induction for gestational diabetes, induction before 24 hours in a woman at full term with ruptured membranes, no signs of infection, and who tests negative for Group B strep (15).