Conclusions
At present, the timing of pregnancy termination is controversial, and many studies are exploring more suitable timings. Studies have shown that elective induction before 39 weeks increases the rate of NICU admission, prolongs the neonatal hospitalization time, results in a high readmission rate within two weeks after delivery, and increases emergency department visits20,21. A large multicentre RCT along with some retrospective studies showed that elective induction at 39 weeks reduced the caesarean section rate, vaginal delivery rate, pregnancy hypertension risk, perinatal infection, neonatal adverse perinatal outcomes (respiratory complications, NICU admission, perinatal death) and did not affect neonatal early literacy and numeracy ability9,22,23. Therefore, elective induction after 39 weeks in low-risk nulliparous women is recommended. However, there is little evidence for elective induction between 40 0/7 and 40 6/7 weeks.
Nowadays, elective labour induction is commonly recommended after 41 weeks in low-risk women without labour onset. The reason for inducing until 41 weeks is to wait for the maturity of the cervix and to have higher chances of spontaneous labour and PROM. However, our study showed no difference in the Bishop scores in the two groups and less opportunity for spontaneous labour and PROM after 41 weeks. If we need to induce these women by AROM or balloon catheter, then there is a higher rate for vaginal delivery at 40 0/7-40 6/7 weeks. Furthermore, we also found decreased intrapartum caesarean section, meconium-stained amniotic fluid, episiotomy and macrosomia rates at 40 0/7-40 6/7 weeks. Studies have shown that the incidence of MSAF increases with gestational age24,25, which is consistent with our findings. Therefore, our study indicated that waiting until 41 weeks in low-risk women was not necessarily beneficial; however, our study is retrospective and needs to be further proven by prospective studies.
An international cohort study showed that after 39 weeks, the risk of PPH increased with gestational age 26. Our results did not reflect this obvious difference, although preliminarily observations indicated that the rate of PPH in the late-term group was slightly greater than that in the full-term group (17% versus 14%, P=0.226). If we increased the amount of data, statistical significance might be obtained. In our study, the prevalence rate of GDM in the full-term group was significantly higher than that in the late-term group. This might be because ACOG recommended that for women with GDM that was controlled with only diet and exercise, it was appropriate to control the gestation period within 40 6/7 weeks 27. Those persisted beyond 41 weeks were due to lack of medical compliance. There was one case of amniotic fluid embolism in our study, which occurred during spontaneous vaginal delivery at 40 3/7 weeks. One hour after delivery, the patient experienced dyspnoea, a sudden drop in blood pressure (86/42 mmHg) and oxygen saturation (80%). After a series of rescue measures, such as open veins, oxygen inhalation, blood pressure boosting, and anti-allergic measures, the final prognosis was good.
Our study indicated that the macrosomia rate was higher at 41 0/7-41 6/7 weeks. No differences in adverse neonatal outcomes were noted in either group, which is consistent with a previous study 21. However, many studies have revealed the risks of macrosomia, such as shoulder dystocia, clavicle fractures, breathing problems, decreased 5-minute Apgar score, hypoglycaemia, meconium aspiration, and more5-8. From this point of view, it is a wise choice to induce at 40 weeks to reduce the risk of macrosomia.
Our conclusion is not to overrule termination timing after 41 weeks. We found that PPH and NICU admission did not increase due to expectations; therefore, termination after 41 weeks cannot be considered inappropriate. For low-risk pregnant women without suspicious macrosomia, we can expect up to 41 weeks according to their willingness. The limitations of our study should also be noted. This study was a single-centre retrospective study, which was small in scale, so increasing the sample size might lead to more significant results.
In conclusion, deliveries at 40 0/7-40 6/7 weeks had better outcomes for low-risk mothers and their babies, such as decreased rates of intrapartum caesarean section, meconium-stained amniotic fluid, episiotomy, and macrosomia, compared with deliveries at 41 0/7-41 6/7 weeks. From our results, we suppose that elective termination at 40 weeks of gestation might be superior to that at 41 weeks in terms of certain maternal and neonatal outcomes. However, in clinical practice, the appropriate termination timing should be discussed and choose a personalized delivery plan. Moreover, the conclusions remain to be further proven by prospective studies.
Acknowledgements: We thank all authors participating in this study.
Funding: This work was funded by Project of Jiangsu Health Commission(H2019008), National Natural Science Foundation of China (81971407), Natural Science Foundation of Jiangsu Province (BK20191070) and Postdoctoral Research Foundation of China (2021M691332)
Declarations of interest: No potential conflict of interest was reported by the author(s)
Author contributions: HY Ren, Q Zuo and XX Zhu: data collection; ZP Ge, HM Lu and ZY Jiang: study design; Y Pan, TT Yin: chart making; Y Yin and M Zhang: data analysis; HY Ren and Y Pan: writing of the report; HM Lu and ZY Jiang: provide financial support and examine and verify the manuscript. All authors have read and approved the manuscript.