VBAC Attempts, Failures Linked to Maternal Age


LOS ANGELES — Older women are less likely to attempt vaginal birth after cesarean delivery and more likely to fail when they do, Sindhu K. Srinivas, M.D., said at the annual meeting of the Society for Gynecologic Investigation.

Dr. Srinivas of the University of Pennsylvania, Philadelphia, presented a retrospective study of 25,005 women who were offered the option of vaginal birth after cesarean (VBAC) delivery at 17 community and university hospitals from 1996 to 2000. While 13,706 women (55%) attempted VBAC, 11,299 (45%) had an elective repeat cesarean section.

“We found as women got older, they attempted [VBAC] much less frequently than other women, but they also failed more,” Dr. Srinivas said. “Biologically why that is the case, we are not quite sure.”

Maternal age did not appear to be associated with risk of complications such as uterine rupture, bowel and bladder injury, blood transfusion, sepsis, and neonatal death. VBAC-related complication rates remained relatively constant in all age groups studied by Dr. Srinivas and her colleagues.

The youngest patients, 922 women ages 15 to 20 years, served as a reference group. A majority of these women—699—chose VBAC.

The largest cohort included 17,415 women, ages 21 to 34 years, 9,801 of whom elected VBAC. Compared with the youngest women, those in this group were about half as likely to attempt VBAC (adjusted odds ratio 0.46) and somewhat more likely to have a failed VBAC (adjusted odds ratio 1.74).

Among 5,574 women ages 35 to 39 years, 2,710 chose VBAC. The likelihood of a woman in this age group electing VBAC was about a third that of the youngest mothers (adjusted odds ratio 0.37). For mothers in their upper 30s, VBAC was more than twice as likely to fail (adjusted odds ratio 2.12).

The oldest group comprised 1,165 women at least 40 years of age. Only 496 in this group opted for VBAC (adjusted odds ratio 0.27), and VBAC was again more than twice as likely to fail (adjusted odds ratio 2.21). All these ratios were highly statistically significant.

The adjusted odds ratios for complications were 1.1 for ages 21-34, 1.03 for ages 35-39, and 0.91 for women 40, none of which approached statistical significance.

Dr. Srinivas' group adjusted the odds ratios to control for factors such as race, insurance type, university hospital, chronic hypertension, preeclampsia, diabetes, prior vaginal deliveries, induced or augmented labor, low birth weight, gestational age, and number of previous cesarean sections.

Some characteristics varied considerably among age cohorts. Black women accounted for two-thirds of all the teenaged mothers. Medicaid covered two-thirds of the teenaged mothers but only 10% of women over the age of 35. The youngest women also were more likely to give birth at a university hospital.

The occurrence of preeclampsia ranged from 3% to 4% across the age groups. Diabetes and chronic hypertension each increased with age: diabetes ranged from 2% to 10% and hypertension ranged from 1% to 6%.

The proportion of women who had previous vaginal deliveries increased from 19% in the youngest group to 31% of women age 40 years and older. Conversely, Pitocin use declined from 32% of all the youngest women to 15% in the oldest cohort.

Next Article: