Comparison of the Effectiveness and Pregnancy Outcomes of Labor Induction with Dinoprostone or Single-Balloon Catheter in Term Nulliparous Women with Borderline Oligohydramnios
Introduction
Amniotic fluid plays a crucial role in fetal well-being during pregnancy, serving as an essential component for normal fetal growth and development. Changes in amniotic fluid volume are significant indicators of placental function. The amniotic fluid index (AFI), measured via ultrasound, is the most commonly used method for assessing amniotic fluid volume. Oligohydramnios is defined as an AFI of ≤5.0 cm, while borderline oligohydramnios (or borderline AFI) is characterized by an AFI ranging from 5.1 to 8.0 cm.
Previous studies have established that oligohydramnios is closely associated with adverse perinatal outcomes, pregnancy complications, and an increased likelihood of cesarean delivery. However, the predictive accuracy of borderline oligohydramnios for adverse perinatal outcomes remains uncertain and controversial. Some studies suggest that borderline oligohydramnios is linked to increased risks of preterm births, cesarean delivery due to non-reassuring fetal heart rate (NRFHR), and fetal growth restriction. Conversely, other studies have found no significant differences in pregnancy outcomes between women with borderline oligohydramnios and those with normal AFI.
Currently, there is no consensus on the optimal induction methods for term pregnancies with borderline oligohydramnios. Chemical methods, such as prostaglandins, and mechanical methods, such as transcervical balloon catheters, are widely used for cervical ripening and labor induction. Prostaglandins are effective for cervical ripening and inducing uterine contractions but can cause uterine overstimulation and changes in fetal heart rate. Transcervical balloon catheters offer an alternative to prostaglandins, particularly in cases of oligohydramnios, fetal growth restriction, asthma, hypertension, and uterine scarring, where prostaglandins pose higher risks. However, studies have indicated that balloon catheters are associated with a higher probability of intra-amniotic infection compared to dinoprostone.
This study aimed to compare the effectiveness and pregnancy outcomes of labor induction using dinoprostone or a single-balloon catheter (SBC) in term nulliparous women with borderline oligohydramnios. The study also sought to identify risk factors for vaginal delivery failure associated with each induction method.
Methods
This retrospective cohort study was conducted at the Women’s Hospital, School of Medicine, Zhejiang University, from January 2016 to November 2018. A total of 244 cases were included, with 103 women undergoing induction with dinoprostone and 141 women undergoing induction with an SBC. The study compared pregnancy outcomes between the two groups, with primary outcomes focusing on successful vaginal delivery rates and secondary outcomes examining maternal and neonatal adverse events.
Ethical approval was obtained from the Ethics Committee of the Women’s Hospital, School of Medicine, Zhejiang University. As a retrospective study, written informed consent was not required, but all patient records were anonymized before analysis.
Inclusion criteria included term nulliparous women (37+0 to 41+6 weeks gestation) with singleton pregnancies, vertex presentation, borderline oligohydramnios (AFI 5.1–8.0 cm), medical indication for labor induction, and an unripe cervix with a Bishop score ≤6. Exclusion criteria included fetal death, malpresentation, twin pregnancies, Bishop score >6, refusal of vaginal delivery, history of cesarean section or uterine surgery, contraindications for vaginal delivery, and cases where induction methods were combined.
Ultrasound examinations were performed to assess gestational age and amniotic fluid volume. The AFI was determined using the four-quadrant technique. Women were informed about the risks and benefits of both induction methods, and informed consent was obtained before induction.
For the dinoprostone group, a single 10 mg slow-release dinoprostone vaginal insert was used for cervical ripening. The insert was removed in cases of uterine hyperstimulation, NRFHR, successful ripening (Bishop score >7), or after 24 hours. Oxytocin augmentation was used if labor progress was insufficient.
For the SBC group, the catheter was filled with up to 150 mL of saline and placed for cervical ripening. The catheter was removed within 24 hours or in cases of discomfort, membrane rupture, active labor onset, or NRFHR. Oxytocin induction was indicated if the cervical score improved.
Fetal heart rate monitoring was performed during induction, and labor was managed according to hospital protocols.
Results
The study included 103 women in the dinoprostone group and 141 women in the SBC group. Baseline characteristics, including maternal age, gravidity, parity, gestational age, BMI, AFI, and initial Bishop score, showed no significant differences between the two groups. However, the dinoprostone group had a higher Bishop score after cervical ripening and a shorter duration of cervical ripening compared to the SBC group.
The successful vaginal delivery rates were similar between the dinoprostone group (64.1%) and the SBC group (59.6%). The incidence of intra-amniotic infection was significantly lower in the dinoprostone group (1.9%) compared to the SBC group (7.8%). Conversely, the occurrence of NRFHR was higher in the dinoprostone group (12.6%) than in the SBC group (0.7%). Oxytocin use was more frequent in the SBC group (85.8%) compared to the dinoprostone group (33.0%).
Multivariate logistic regression analysis showed that nuchal cord was a significant risk factor for vaginal delivery failure in the dinoprostone group (adjusted odds ratio [aOR]: 6.71, 95% confidence interval [CI]: 1.96–22.95). In the SBC group, gestational age (aOR: 1.51, 95% CI: 1.07–2.14), BMI >30 kg/m2 (aOR: 2.98, 95% CI: 1.10–8.02), and fetal weight >3500 g (aOR: 2.49, 95% CI: 1.12–5.50) were identified as risk factors for vaginal delivery failure.
Discussion
The study found that term nulliparous women with borderline oligohydramnios had similar successful vaginal delivery rates when induced with dinoprostone or an SBC. However, each method had distinct advantages and disadvantages. Dinoprostone was associated with a lower incidence of intra-amniotic infection but a higher risk of NRFHR. In contrast, the SBC was associated with a higher risk of intra-amniotic infection but a lower risk of NRFHR.
Nuchal cord was identified as a significant risk factor for vaginal delivery failure in the dinoprostone group. This finding suggests that ultrasound examination to detect nuchal cord before induction is crucial for selecting the appropriate induction method. For women with nuchal cord, the use of an SBC may reduce the risk of uterine overstimulation and fetal heart rate changes associated with dinoprostone.
In the SBC group, increased gestational age, BMI >30 kg/m2, and fetal weight >3500 g were associated with a higher risk of vaginal delivery failure. These findings highlight the importance of considering maternal and fetal factors when selecting induction methods.
The study also noted that obese women (BMI >30 kg/m2) had a higher risk of vaginal delivery failure when induced with an SBC. This suggests that alternative induction methods may be more suitable for obese women, although further research is needed to confirm this.
Limitations
This study has several limitations. First, its retrospective nature may introduce collection bias. Second, the sample size was insufficient to definitively determine the optimal induction method for women with nuchal cord or obesity. Third, other factors influencing vaginal delivery success were not analyzed.
Conclusion
Term nulliparous women with borderline oligohydramnios have similar successful vaginal delivery rates when induced with dinoprostone or an SBC. However, the choice of induction method should consider specific risk factors, such as nuchal cord, BMI, gestational age, and fetal weight. For women with nuchal cord, the SBC may be preferable due to the lower risk of uterine overstimulation. For obese women, alternative induction methods may be more effective, although further research is needed to confirm this.
doi.org/10.1097/CM9.0000000000001881
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