Based on our best knowledge, this is the first report that investigates the effects of delivery mode on ovarian reserve. The objective of this study was to evaluate the effect of CS in comparison with VD on ovarian reserve. In the present study, ovarian reserve has been assessed by means of maternal serum AMH and AFC. The results showed that delivery mode had no effect on ovarian reserve after adjusting for women’s age, baseline AMH, BMI, gestational age at delivery, breastfeeding, postpartum menstruation, neonatal sex and neonatal weight.
Over the recent years, several observational studies have examined the relationship between CS and future fertility and some of them concluded that the prevalence of subsequent pregnancy following CS declined [3,4,5,6,7]. Nevertheless, some other studies have not seen such a relationship [1, 3]. Two systematic review and meta-analysis have been conducted on the effect of CS on future fertility and pregnancy [4, 7]. In one of them, it was concluded that CS might have a negative impact on future pregnancies but nonexperimental survey data and selection bias in its included studies were likely to affect the results . As the previous study, the results of the other systematic review showed that CS is correlated with decreased subsequent fertility in comparison with VD . But according to characteristics of included studies in this review article that some of them had not had risk adjustment, we think that the results should be interpreted with caution. The authors also stated that even if there is an impact of CS on subsequent pregnancy, this effect is meager . As it is clear from the above, most previous studies that examined the effect of CS on fertility have assessed this effect based on the incidence of subsequent pregnancy. Since subsequent pregnancy can be influenced by several confounding factors, we have investigated the effect of CS on fertility using its impact on ovarian reserve.
Engin Oral and KorayElter concluded that the effect of CS on future fertility is most likely due to some other confounding factors, rather than due to surgical impact of CS .
Many studies have also been carried out done about the effects of various types of pelvic surgery on ovarian reserve [14,15,16] and some of them have demonstrated that pelvic surgery may affect ovarian blood supply [14, 16]. Although we did not find any relationship between the CS and ovarian reserve, during CS, as with any other surgery, there is a potential risk of pelvic organs and vessels trauma due to pelvic manipulations and inflammatory mediators releases, which may lead to decreasing ovarian reserve.
Over the course of recent years, some studies have been conducted to evaluate AMH during pregnancy and postpartum [17,18,19,20,21], and it has been revealed that pregnancy has significant effect on serum AMH level in such a way that AMH level decreases progressively by advancing gestational age and maximum effect has been found in third trimester [19,20,21] Also in our study, the levels of serum AMH at the end of third trimester were lower than six months after delivery. On the other hand, in recent years, researchers have considered the relationship between serum AMH and adverse pregnancy outcomes [22,23,24]. Considering that there is still no consensus on the impact of pregnancy outcomes on the level of AMH and ovarian reserve and also our objective was to examine the effect of delivery type on the ovarian reserve, we tried to eliminate any potential factor that had effect on AMH. Therefore, all women who had any adverse pregnancy outcomes and postpartum complications were excluded from the study.
It is well-known that ovarian reserve decrease with increasing age. Although it may seem that a period of 6 months may be too short to judge about future fertility, many other factors might affect ovarian reserve over the course of time other than delivery mode. So, we decided to evaluate ovarian reserve no later than 6 months after delivery. We could not prove any association between CS and ovarian reserve but CS may cause subsequent infertility and subfertility through different mechanisms. Effect on the endometrial cavity and ensuing implantation and placentation, pelvic adhesion, and the possibility of affecting the pelvic organs blood supply, all can be considered as contributing factors in reducing fertility following CS. Also, uterine manipulation during CS and potential complications such as bleeding and infection may have a negative impact on ovarian reserve, so the results of our study should be interpreted with caution and much more studies are needed about this subject. We believe that association between delivery mode and ovarian reserve is yet to be studied.
One of the strengths of our study is that there was the least level of heterogeneity among the participants. Only singleton pregnancies were examined and participants were limited to women who had not had previous pregnancies and none of them had had underlying disease. There is controversy over the effect of smoking on AMH levels. Some studies have reported a decrease in blood hormone levels following smoking [25, 26], while others have shown no effect [27,28,29]. Given the uncertainty about the impact of smoking on serum AMH levels, we did not include smoker women in this study. On the other hand, due to the effect of contraceptive pills on the level of AMH and AFC, participants who had consumed various hormonal medications were excluded from the study. With reference to the above explanation, we tried to eliminate the confounding factors as much as possible, so that the effect of CS on ovarian reserve has been more accurately examined. Of course, there were some inevitable factors that might affect AMH concentration and AFC. One of these factors was breastfeeding that whose relationship with AMH concentration and ovarian reserve has not been identified in previous studies yet. The other inevitable factor is fetal sex. It is prominent that AMH blood concentration is higher in male fetuses. So, most probably fetal sex can affect the AMH concentration in maternal serum, as it has been observed in a study that serum AMH levels are significantly higher in mothers who have had a male fetus . Considering the possible impact of these factors on the study outcomes, we analyzed their effect and it was demonstrated that the relationship between delivery mode and ovarian reserve was not affected by breastfeeding and the fetal sex.
One of the limitations of our study is that we did not differentiate between emergency and elective cesareans and also did not consider cervical dilatation and effacement during emergency cesarean section. However, since in this study CS has not had an effect on ovarian reserve, it does not seem that this limitation has a significant effect on the results. Another limitation of our study is AFC measurement timing. It is well-known that the best time to measure AFC is the third day of the menstrual cycle. However, a retrospective cohort study showed that AFC retains its predictive value when measured at different phases of the menstrual cycle . In our study, some women experienced amenorrhea due to breastfeeding. Therefore, in this group of women, we had to measure AFC regardless of the menstrual cycle. However, using the Multiple Linear Regression Model, there was no difference in the AFC based on the existence of amenorrhea or not.