In the presence of an unfavorable cervix, induction of labor can increase the possibility of prolonged labor and incidence of C-Sect. (18). Therefore, different methods have been used for cervical ripening prior to labor induction. To the best of our knowledge, our research is the second study comparing FC with vaginal misoprostol for cervical ripening in postdate primigravid pregnancies since the study performed by Kandil et al. in 2010 (19).
We found that placental abruption and uterine tachysystole occur less frequently with FC while increasing oxytocin requirement and labor duration compared to vaginal misoprostol. Moreover, the risk of C-section, NICU admission, and AF meconium staining, was lower in the FC group compared to the misoprostol group, but not at a statistically significant level. Kandil et al.’s findings were similar with respect to the higher need for oxytocin augmentation in the FC group; however, contrary to our study, they found that induction-delivery interval is significantly shorter with FC (19). The discrepancy between the two studies can be explained by the difference in study designs, the sample size, and the demographic characteristics of the participants.
In addition, Kandil et al. reported no NICU admission in either of the groups (19). Furthermore, consistent with our results, Noor et al. found no significant difference in NICU admission between the misoprostol and FC groups (18).
Garba et al. also conducted a study on postdate pregnancies, reporting a significantly shorter induction-delivery interval in the misoprostol group and comparable maternal and neonatal outcomes in both groups (20); however, women of their study were all multigravida and oxytocin was synchronously infused in the FC group, which makes it different from the current study.
Noor et al. conducted a study on women with term gestation comparing 25 µg vaginal misoprostol given every 4 hours to 16 Fr FC inflated with 50 ml of sterile saline (18). Their results regarding the induction to delivery interval and uterine hyperstimulation were in line with our findings; nevertheless, the rate of NVD was significantly higher in the misoprostol group of their study. Their study included both primigravid and multigravida term pregnancies with different indications for labor induction, while we only recruited primigravid women with postdate pregnancy as an indication for labor induction, which may be the reason for the difference between their results and ours. Also, contrary to our findings, Tuuli et al. reported no significant difference in the total duration of labor in the misoprostol group compared to the FC group (21). The shorter duration of labor in the misoprostol group our study can be justified by the greater effect of misoprostol due to direct delivery to myometrium through cervical canal via the vaginal route.
Gondkar et al. suggested equal efficacy and safety of FC and vaginal misoprostol for labor induction (22). Similarly, Fox et al. found FC and vaginal misoprostol to be equally effective as induction agents (23). Nonetheless, in this meta-analysis of 1603 patients, the rate of uterine tachysystole was significantly higher in patients receiving misoprostol compared with women receiving transcervical FC, which is consistent with our results. The lower rate of tachysystole with FC is particularly important in patients at increased risk of fetal hypoxia, such as those with postdate pregnancy since varying degrees of placental insufficiency may be present in this population.
In accordance with our findings, Jozwiak et al. demonstrated that oxytocin is significantly more often required when FC is used (24). As they suggested, this can be interpreted into the inability of FC to cause contractions. In their opinion, FC can merely ripen the cervix, an advantage for cases of intolerability for contractions including intrauterine growth retardation of oligohydramnios (24).
Some studies have investigated the effect of FC combined with vaginal misoprostol. As a matter of fact, the use of intracervical FC plus vaginal misoprostol has been compared with vaginal misoprostol alone in a very recent meta-analysis. In this study, Lee et al. showed that induction time, uterine tachysystole, and meconium staining decrease with the combination of FC and vaginal misoprostol compared to misoprostol alone with no difference regarding the C-section rate (25).
One limitation of the current study was the impossibility of blinding due to the nature of the interventions, which can make the assessment of outcomes prone to bias. Another limitation of our study was that we did not take infections into account. FC insertion has been reported as a risk factor for chorioamnionitis in a recent meta-analysis (26). Besides, in the only other study performed on postdate primigravid women, prophylactic ampicillin was administered in the FC group to prevent infection (19). Various volumes have been used to fill the FC balloon across different studies and some studies suggest that higher volumes are more effective for labor induction (27, 28). We might have achieved better results regarding the rate of NVD in the FC group if we had used 50 ml of sterile saline for FC balloon inflation instead of 30 ml.