Caroline Helwick

February 10, 2014

NEW ORLEANS — The number of previous cesarean deliveries a woman has undergone has an effect on the optimal time for subsequent cesarean delivery, according to a new study of almost 6500 women.

"Waiting until 39 weeks increases maternal risk," said Laura Hart, MD, a fellow in the division of maternal fetal medicine at the University of Texas Health Science Center in Houston. "The optimal time of delivery is 38 weeks for women with 2 previous cesarean deliveries and 37 weeks for those with 3 or more."

"To our knowledge, this is the first study to analyze maternal and perinatal morbidity by the number of previous cesarean deliveries," said Dr. Hart, who presented the results here at the Society for Maternal-Fetal Medicine 34th Annual Meeting.

Currently, 22% of women undergo a cesarean procedure for their first delivery, and the rate of vaginal birth after a cesarean delivery is about 9%. "The combination of these trends has led to more than 600,000 women per year having repeat cesarean sections," she reported.

"We are commonly faced with the dilemma of when to deliver these women," she said. Clinicians attempt to balance the risks and benefits of early-term delivery — especially concerns about perinatal morbidity and mortality — against the benchmark of reaching a gestational age of 39 weeks.

"Despite the intention to wait until 39 weeks, some women will go into labor, have spontaneous rupture of membranes, experience placenta abruption, or develop complications such as hypertension," she noted. This often leads to more unscheduled and emergency cesarean deliveries, which can increase the risk for further complications.

Delivery before 39 weeks has been discouraged for uncomplicated pregnancies because of concerns about neonatal morbidity in early-term infants. However, supporting data are limited, said Dr. Hart, and the wait could actually increase the risk for women with multiple previous cesarean deliveries.

Study Details

To determine the optimal delivery time for women with 2 or more previous cesarean deliveries, Dr. Hart and her colleagues performed a secondary analysis of the Maternal Fetal Medicine Units Network Cesarean Section Registry.

They identified 6435 women who delivered a singleton weighing more than 500 g at a gestational age of at least 20 weeks. All women had undergone at least 2 previous low transverse cesarean deliveries and had plans for a repeat procedure; all delivered at 37 weeks or later.

The researchers evaluated the risk for adverse maternal and perinatal outcomes on the basis of the timing of delivery in women with 2 previous cesarean deliveries and in those with 3 or more.

Delivery at 39 Weeks Not Optimal

Only about 60% of women with 2 previous cesarean deliveries were able to delay delivery until 39 weeks, and only about 50% of those with 3 or more.

Table. Gestational Age at Delivery in the Study Cohort

Gestational Age at Delivery (Weeks) 2 Previous Cesarean Deliveries (%) ≥3 Previous Cesarean Deliveries (%)
37 11 15
38 31 35
39 46 41
≥40 13 9


When stratified by gestational age at delivery, clinical characteristics — including age, body mass index, smoking status, race/ethnicity, and insurance status — were similar in the 2 groups of women.

However, "complication rates were significantly different across gestational ages for both maternal and neonatal outcomes," Dr. Hart reported.

For women with 2 previous cesarean deliveries, the risk for adverse maternal outcomes was 3.3 per 1000 women undelivered. As gestational age at delivery increased, so did this risk, which approached 15.0 per 1000 for delivery at 39 weeks. There was no significant difference between delivery at 37 weeks and 38 weeks, but there was a significant 3-fold difference between delivery at 38 weeks and 39 weeks (P = 0.03).

Adverse perinatal outcomes did not significantly increase until 39 weeks in this group.

There is enormous clinical pressure not to do deliveries prior to 39 weeks.

For women with 3 or more previous cesarean deliveries, the risk for adverse maternal outcome was significantly greater with delivery at 40 weeks than at 37 weeks (P = .02). The risk rose from less than 5.0 per 1000 deliveries at week 37 to 30.0 at week 39 and to 50.0 at week 40.

In this group, the risk for adverse perinatal outcome did not increase until 39 weeks, but was significantly higher with delivery at week 40 than at week 39 (P = .04).

"There's a linear increase in maternal risk starting at 37 weeks, which is a full 2 weeks before any increase in perinatal risk," emphasized Dr. Hart.

"We conclude that the optimal time of delivery is 38 weeks for women with 2 previous cesarean deliveries and 37 weeks for those with 3 or more," she said.

"This was an outstanding study," said Mary D'Alton, MD, the Willard C. Rappleye professor of obstetrics and gynecology, and chair of the Department of Obstetrics and Gynecology at the Columbia University College of Physicians and Surgeons in New York City.

"It's extremely clinically relevant, because there is enormous clinical pressure put on our labor and delivery units not to do deliveries prior to 39 weeks," she told Medscape Medical News. "However, we all know there are certain circumstances where delivery prior to 39 weeks is indicated to prevent significant maternal and fetal morbidity," she explained.

"This study gives us data from a very large dataset, totally verified for quality, that will change clinical practice," she concluded.

Dr. Hart and Dr. D'Alton have disclosed no relevant financial relationships.

Society for Maternal-Fetal Medicine (SMFM) 34th Annual Meeting: Abstract 40. Presented February 7, 2014.


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