NEW YORK (Reuters Health) – When a transcervical Foley catheter is used to help induce labor, filling a 30-mL balloon at the tip with 60 mL of saline is more likely to result in delivery within 12 hours than filling it with 30 mL, according to a report in the June Obstetrics & Gynecology.

“For health care providers who only have the 30-mL Foley balloon tip, our study suggests that inflating to a volume of 60 mL is safe and potentially beneficial,” the researchers said.

Earlier randomized trials comparing 30-mL and 80-mL balloons for this purpose found higher 24-hour delivery rates with the larger balloons, but there have been no reports of a 30-mL balloon inflated to varying volumes, according to lead author Dr. Shani Delaney from the University of Washington in Seattle and colleagues.

For the current randomized trial, the researchers used a Bard 18-French Foley catheter with a 30-mL balloon tip inflated to either 30 mL or 60 mL. They recruited 192 women with term, vertex, singleton pregnancies and a Bishop score less than 5, indicating that labor was unlikely to start without induction. Within half an hour after the catheter was placed, oxytocin was started. There were no complications associated with placement or inflation of the balloons.

The primary outcome — delivery within 24 hours — did not differ between the 30-mL (60/94, 64%) and 60-mL (65/98, 66%) groups. But by 12 hours, 25 women in the 60-mL group (26%) had delivered, vs 13 (14%) in the 30-mL group (p = 0.04).

“With a 12% absolute risk increase for delivery within 12 hours among the 60-mL arm, the number needed to treat to achieve this outcome is only nine women,” the investigators say.

Median cervical dilation was 4 cm in the 60-mL arm vs 3 cm in the 30-mL arm (p < 0.01), but there was no difference in other secondary outcomes, including cesarean delivery rate, operative vaginal delivery rate, absolute time to delivery, maximum oxytocin dose, perinatal complications, or neonatal outcomes. In multivariable analysis, inflation to 60-mL was associated with an 84% higher likelihood of delivery within 12 hours, compared with inflation to 30-mL. The difference in delivery rate within 12 hours was prominent only in nulliparas. In these women, the 60-mL volume increased the odds of early delivery 2.88-fold. Among multiparas, there was no difference in the rate of delivery within 12 hours according to inflation volume. However, multiparas accounted for only about a quarter of the women in each group. “We recommend considering a 60-mL Foley balloon for induction of labor, particularly in nulliparous women,” the researchers conclude. Reference:
Obstet Gynecol 2010;115:1239-1245.