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Women who delivered their first child by cesarean section were less likely to have another baby within the next 3 years than those who delivered vaginally, according to a prospective cohort study.

C-section was associated with a 15% lesser chance of conception than vaginal birth during 3 years of subsequent follow-up, whether or not women were trying to conceive (adjusted hazard ratio 0.85, 95% CI 0.74-0.96), reported Kristen Kjerulff, PhD, of the Penn State College of Medicine in Hershey, and colleagues.

Women who delivered their first child via C-section were also less likely to have a subsequent live birth than women who delivered vaginally (42.8% v.s. 50.1%, respectively), researchers wrote in .

In an interview with 番茄社区app, Kjerulff hypothesized that physiological differences in women related to the mode of their first delivery affects future ability to get pregnant. She noted, too, that some women develop a defect at the site of the C-section incision -- a niche -- that may result in a low-grade infection that can impair fertility.

Wendy Kuohung, MD, of Boston University School of Medicine and Boston Medical Center, said that this is the first large-scale prospective study that investigates whether mode of delivery impacts future conception and live birth.

"It's a big concern because the cesarean rate is so high in the U.S," she told 番茄社区app.

But Kuohung, who was not involved in the study, also said that the direction of causality is still a question.

"The cesarean procedure itself may not necessarily be the cause of lower subsequent rates of conception," Kuohung said. "Rather, having to undergo a cesarean may be a sign that these are women who already had impaired reproduction."

Previous research indicated that women who deliver via C-section have lower rates of future conception, but few studies have addressed the role of plans to conceive or the nature of the cesarean delivery itself, Kjerulff and colleagues wrote. That prompted the group to conduct the First Baby Study involving a prospective, multicenter cohort of more than 3,000 nulliparous women in Pennsylvania. Study participants were enrolled during pregnancy and followed through 36 months postpartum.

Researchers interviewed study participants once during pregnancy, and every six months during the postpartum period. Interviews measured unprotected sex and conception rates across the three-year follow-up. Conceptions included those that did not result in a live birth.

The researchers measured for covariates including, but not limited to, demographic factors, plans to have another child within three years, prepregnancy BMI, prior infertility, and indications for cesarean delivery such as chronic and gestational hypertension, preeclampsia, diabetes, and soft-tissue disorders such as uterine fibroids..

Of the 3,000 women in the study, 2,423 completed the three-year follow-up. Factors associated with loss to follow-up included non-white race, having less than a college degree, and being unmarried.

Just under 30% of participants delivered their first child via C-section. They were more likely to be older, more overweight, and to have sought out fertility advice or treatment, compared with participants delivering vaginally.

Participants did not differ by mode of delivery regarding plans to conceive in three years, whether or not they had unprotected sex during the follow-up period, the frequency of unprotected sex each month, and the mean age of their first child when they began having unprotected sex.

Limitations to the study included its restriction to one U.S. state; participants were also majority white, and of higher socioeconomic status than the general population at first childbirth. In addition, women self-reported rates of unprotected sex, birth control use, and pregnancy outcomes, which may subject these results to recall bias.

While further research is needed regarding indications for cesarean delivery, Kuohung said that these results were strong enough to warrant clinical attention: "In light of the study findings, I think the important thing is to reduce the cesarean rate as much as is feasible," she said.

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