Perinatal death risk in term VBAC pegged at 1:1,000; Risk was twice as high as that seen in other multiparous women, Scottish data show. (First Study of Uncomplicated Pregnancies).

LOS ANGELES -- The absolute risk of perinatal death due to any cause for a healthy singleton fetus in cephalic presentation at term in a woman attempting vaginal birth after a prior cesarean section is similar to the risk in nulliparous women.

That risk--about 1 fetal death per 1,000 deliveries--was based on findings from a study of more than 300,000 births reported by Dr. Gordon C.S. Smith at the annual meeting of the Society for Gynecologic Investigation.

When women attempting vaginal birth after a prior cesarean section (VBAC) were compared with multiparous women, however, the overall risk of perinatal death was twice as high because of higher rates of fetal death due to uterine rupture and other anoxic deaths. The rate of perinatal death due to intrapartum anoxia was nearly three times higher in VBAC deliveries than in babies delivered from other multiparous women. The lowest perinatal death rate was in women undergoing elective repeat C-section: 1 death in a total of 9,014 deliveries, Dr. Smith of Cambridge (England) University said in a poster presentation at the meeting.

The risk of perinatal death due to uterine rupture specifically was eight times higher in women attempting VBAC--1 death per 2,000 deliveries--compared with the risk in nulliparous women or in other multiparous women.

Previous studies of perinatal death with VBAC included preterm births or breech deliveries, which elevated the estimated risks of perinatal death from successful VBAC or unplanned repeat C-section. This is the first large study of VBAC risks in otherwise uncomplicated pregnancies at term, he said.

The investigators matched data from all births in Scotland during a 5-year period (1992-1997) with data from a national register of perinatal deaths to evaluate delivery-related perinatal deaths, defined as intrapartum stillbirth or neonatal death unrelated to congenital anomaly. Their analysis included data on 313,238 singleton births with cephalic presentations delivered between 27 and 43 weeks' gestation. They excluded multiple pregnancies, non-cephalic presentations, deliveries before 37 weeks' or after 43 weeks' gestation, planned first-time C-sections, perinatal deaths due to congenital anomalies, and antepartum stillbirths,

Dr. Smith's study did not include figures on the number of inductions that were performed. A previously published study by Seattle investigators showed that, compared with women undergoing repeat elective C-section, those who were attempting VBAC with spontaneous labor were at three times the risk of uterine rupture. Women who were induced had 4.9 times the risk if prostaglandins weren't used, and their risk increased almost 15 times if prostaglandins were used (N. Engl. J. Med. 345[1]:3-8, 2001).