Study population
This retrospective cohort study assessed data from the obstetrics department of Jiangsu Province Hospital from January 1st to December 31st, 2020. These data included all maternal medical records and neonatal deliveries. The inclusion criteria were a low-risk singleton pregnancy delivered at 40 0/7-41 6/7 weeks of gestation at our hospital. Low risk was defined as the absence of any condition that might be a maternal or foetal indication for delivery in a short time, such as any antepartum hypertensive disorder, cardiac disease or renal insufficiency9. Cases with electing caesarean delivery, vaginal birth after caesarean section (VBAC) and partial data loss were excluded. We divided pregnancies meeting the inclusion criteria into a full-term group (40 0/7-40 6/7 weeks) and a late-term group (41 0/7-41 6/7 weeks)10. This study was approved by the Ethics Committee of Jiangsu Province Hospital [Ethics Committee 2020-SR-256].