To explore effects of one-off single balloon cervical dilator (hereinafter referred as ballon) used for labor induction in full-term parturients with isolated borderline oligohydramnios (IBO) and isolated oligohydramnios (IO) and their pregnancy outcomes.

A total of 346 parturients who were hospitalized in Northern Jiangsu People′s Hospital from June 2018 to June 2020 with labor induction by balloon were selected as research subjects. According to amniotic fluid index (AFI) of parturients in the third trimester, they were divided into IBO group (n=135, 5 cm<AFI≤8 cm), IO group (n=38, AFI≤5 cm), and control group (n=173, parturients with normal AFI). The gestational age of placing balloon, Bishop scores before and after placement, effective rate of cervical maturation, vaginal delivery rate, rate of transition to emergency cesarean section, duration of the first labor, postpartum adverse pregnancy outcomes (amniotic fluid meconium contamination, postpartum fever, postpartum hemorrhage) and related complications of balloon, and newborn outcomes were observed and were compared by one-way ANOVA, Kruskal-Wallis H test, and chi-square test among three groups. Least significant difference (LSD)-t test and Bonferroni method for adjusting the significant level (α′=0.05/3=0.017) were used for further comparisons. There were no statistical differences in general clinical data among three groups, such as age, gravidity, body mass index (BMI), and so on (P>0.05). The procedure followed in this study complied with the requirements of the World Medical Association Declaration of Helsinki revised in 2013.

①After labor induction by balloon in IBO group, IO group, and control group, cervical Bishop scores were (7.7±1.6) scores, (8.1±1.5) scores and (8.0±1.5) scores respectively, which were significantly increased compared with those (3.1±0.5) scores, (3.1± 0.7) scores and (3.2±0.6) scores before labor induction, and all the differences were statistically significant (t=-31.883, -19.546, -37.544; P<0.001). There were no statistical differences in cervical Bishop scores before and after balloon placement, and total effective rate of promoting cervical ripening among three groups (P>0.05). ②The gestational ages of parturients in IBO group, IO group, and control group were 39.7 weeks (39.3-40.1 weeks), 38.9 weeks (37.8-39.7 weeks), and 40.4 weeks (40.3-40.6 weeks), respectively, and the difference was statistically significant (χ²=157.093, P<0.001). Further pairwise comparison results showed that the gestational ages of placing balloon of parturients in IBO group and IO group were significantly lower than that of control group, and IBO group was significantly lower than that in IO group, and all differences were statistically significant (P<0.001, <0.001, =0.006). There was statistical difference in constituent ratio of delivery methods among three groups (χ²=6.565, P=0.038), and further pairwise comparison results showed that the rate of emergency cesarean section in IO group was statistically higher than that of control group, and the difference was statistically significant (28.9% vs 12.7%, χ²=6.221, P=0.013). Comparison of the proportion of parturients undergoing emergency cesarean section due to abnormal fetal heart rate monitoring among three groups was statistically significant (χ²=7.649, P=0.022), and further pairwise comparison results showed that the rate of IO group was higher than that of control group, and the difference was statistically significant (72.7% vs 22.7%, P=0.003). ③There was statistically significant difference in the incidence of meconium contamination among three groups (χ²=11.368, P=0.003), and further pairwise comparison results showed that the incidence in IO group was statistically higher than those in IBO group and control group (23.7% vs 7.4% and 6.9%, P=0.008, 0.005). Comparison of the incidence of postpartum fever among three groups was statistically significant (χ²=8.109, P=0.015), and further pairwise comparison results showed that the incidence in IO group was statistically higher that in control group (P=0.010). There were no statistical differences in duration of the first labor and incidence of related complications of balloon among three groups (P>0.05). ④The comparison of birth weights of neonates among three groups was statistically significant (F=7.677, P=0.001), and further pairwise comparison results showed that birth weight of neonates in IO group was significantly lower than that of IBO group and control group [(3 186.8±278.2) g vs (3 353.6±335.1) g and (3 405.3±301.1) g, P=0.004, <0.001]. Apgar scores at 1 min after birth and proportion of neonates transferred to neonatal intensive care unit (NICU) among three groups showed no significant differences (P>0.05).

IBO and IO in the third trimester can lead to iatrogenic preterm birth. The use of balloon for labor induction can effectively promote cervical ripening without increasing the incidence of related complications of balloon and affecting the first stage of labor.