Cesarean deliveries linked to reduced fecundability and increased infertility risk

Fecundability ratio is reduced among women with more than 1 children reporting a previous cesarean delivery (CD) vs vaginal delivery, while the risk of infertility is increased, according to a recent study published in the American Journal of Obstetrics & Gynecology.

The time to pregnancy (TTP) refers to the duration of attempts toward conception before success. This is used to measure fecundability, defined as the ability to establish clinical pregnancy in a cycle. Decreased fecundability is reported in patients with infertility, defined as unsuccessful conception with over 12 months of attempts.

It is unclear how CD impacts future infertility, with most studies about this association using interpregnancy interval to measure fecundability. Few studies have evaluated the possibility of a bidirectional relationship between CD and fecundability. Investigators conducted a prospective cohort study to assess this relationship.

Women participating in the Norwegian Mother, Father, and Child Cohort Study (MoBa) were included in the analysis. Data was obtained from self-reported questionnaires at 15 to 18 weeks’ gestation, while additional information about maternal health and pregnancy outcomes was obtained from the Medical Birth Registry of Norway.

Participants included women with at least 1 recorded pregnancy in MoBa with complete TTP data and who filled out the recruitment questionnaire. The MoBa pregnancy was considered the index pregnancy among these patients. Additionally, women with CD history were excluded because of their high likelihood of recurrence.

Women were asked at recruitment if their pregnancy was planned, and those with planned pregnancy were asked how long they had been trying to conceive. Options included under 1 month, 1 to 2 months, and 3 or more months, with participants choosing the latter options asked to specify an exact number of months.

Alongside questions pertaining to planned pregnancy, participants were asked about their average cycle length, which was used to correct TTP. Reporting a duration to conceive of over 3 months without specifying an exact number of months occurred in 10.1% of participants. The duration was assumed to be 3 months in these individuals.

Covariates included maternal age, education, smoking status, and prepregnancy body mass index. Chronic conditions such as arthritis, asthma, endometriosis, hyper- and hypothyroidism, myoma, and ovarian cysts were also considered.

There were 42,379 pregnancies of women with previous birth included in the analysis of previous cesarean delivery and fecundability, of whom 2 in 3 had only 1 prior birth. Women with prior CD had an older age, lower education, and higher rates of chronic conditions and complications vs women with prior vaginal delivery.

Women with a prior CD had a lower fecundability ratio than those with prior vaginal delivery, with absolute infertility risks of 9.9% and 7.3%, respectively. This indicated a corresponding risk ratio of 1.21 for women with previous CD.

Similar results were reported when excluding women aged 35 years or older or pregnancies with a TTP of 3 or more months. Planned and emergency CDs also had similar fecundability patterns.

When evaluating the impact of fecundability on CD risk, 74,024 index pregnancies were included in the analysis, 10.9% of which were to women with infertility. Lower education, increased smoking, higher rates of overweight and obesity, and more chronic conditions and pregnancy complications were reported in women with infertility.

An association was reported between a higher number of cycles to achieve pregnancy and increased CD risk. Conception within the first 2 cycles was associated with a 10.3% absolute risk of CD, vs 17.6% for 12 or more cycles. This pattern did not change when adjusting for complications in the index pregnancy or including women with a prior CD.

These results indicated a bidirectional relationship between fecundability and CD. Investigators concluded, “there may be common underlying explanatory mechanisms and that the surgical procedure itself may not or only partly directly influence fecundability.”

Reference

Sima YT, Magnus MC, Kvalvik LG, et al. The relationship between cesarean delivery and fecundability: a population-based cohort study. Am J Obstet Gynecol. 2024;230:667.e1-21. doi:10.1016/j.ajog.2023.10.029