The China Labor and Delivery Survey was a nationwide cross-sectional study conducted from March 1, 2015 to December 31, 2016. The participating hospitals were solicited through obstetric networks. Hospitals with 1000 or more deliveries per year were eligible for inclusion. Depending on the annual delivery volume of the hospitals, 5–10 consecutive weeks were randomly selected in a 12-month period as the study window. Within the selected weeks, all births at ≥ 24 weeks of gestation or with a birthweight of ≥ 500 g were included. We obtained anonymized data from participants’ medical records; information on maternal sociodemographic characteristics, medical and pregnancy histories, pregnancy and labor complications, and perinatal outcomes was extracted by trained staff. Criteria for data extraction were defined in an operations manual that was used for staff training and monitoring of data collection. The completed data-extraction forms were reviewed by the data manager for completeness before they were entered into the database. Methodological details on sampling, data extraction, and data management have been published elsewhere [12, 13].
A total of 96 hospitals distributed in 24 (out of 34) provinces, autonomous regions and municipalities in China were included in the analysis. This study was approved by the Ethics Review Board of the Xinhua Hospital Affiliated to the Shanghai Jiao Tong University School of Medicine (XHEC–C–2015–006), the Research Project Review Panel (RP2) of the UNDP/UNFPA/UNICEF/WHO/World Bank Special Programme of Research, Development and Research Training in Human Reproduction, at the Department of Sexual and Reproductive Health and Research at the World Health Organization, by the WHO Research Ethics Review Committee (HRP Study A65899) and participating hospitals.
Labor induction was defined as the process of artificial stimulation of the uterus to start labor . A woman was considered to have undergone labor induction if an induction, or the method or start time thereof was recorded before the onset of labor. Gestational age was ascertained on the basis of the last menstrual period, or by ultrasound dating in the first trimester if the date of the last menstrual period was uncertain. Standard partitioning of geographical regions in China (East, North, South, Central, Northeast, Northwest, and Southwest) was used to reveal regional differences . Hospital levels were determined by the Chinese Ministry of Health based on the number of beds, categories of clinical departments, numbers of medical staff, type and quantity of equipment, and hospital funding . Labor analgesia included epidural analgesia and other relaxation techniques for pain management.
Indications for labor induction included gestational hypertension, preeclampsia/eclampsia, gestational diabetes, premature rupture of membranes (PROM), late-term and post-term pregnancies, fetal death, maternal medical complications (e.g., diabetes mellitus, renal disease, autoimmune disease), and fetal conditions (e.g., small for gestational age [SGA], abnormal antenatal testing results, fetal anomalies). Late-term pregnancy was defined as a pregnancy reaching 41–41+6 weeks of gestation, whereas a post-term pregnancy was defined as a pregnancy reaching or exceeding 42 weeks of gestation . SGA was determined as a birthweight less than the 10th percentile for a given gestational week based on a global reference for fetal-weight and birthweight percentiles . Macrosomia was defined as a birthweight of ≥ 4000 g, regardless of the gestational age . Abnormal or indeterminate fetal heart rate tracings or abnormal biophysical profiles were considered abnormal antenatal testing results. An induction performed when there were no maternal or fetal medical conditions or obstetric complications, while the gestational age was less than 41 weeks, was categorized as nonmedically indicated. A uterine scar could be due to either a previous cesarean delivery or other uterine surgery.
We used a simplified Bishop score, comprised of cervical dilation, effacement, and fetal station, to assess cervical readiness for induction. A simplified Bishop score ≤ 4 was considered indicative of an unripe cervix, which has a similar sensitivity and specificity to an original Bishop score ≤ 6, the definition of an unfavorable cervix . Methods of induction were grouped into artificial rupture of membranes, mechanical methods, and use of prostaglandin and oxytocin. We did not exclude any births based on the method used for cervical ripening and labor induction. The attempted mode of delivery was recorded in the medical records when women were admitted to hospitals, as one of the following: spontaneous labor, labor induction, cesarean delivery without indications, cesarean delivery with indications, and unknown.
We further compared labor induction and prelabor cesarean delivery in low-risk women on maternal and neonatal outcomes. Low-risk was defined as term pregnancies without any of the following maternal or fetal medical conditions or obstetrical complications: chronic hypertension, diabetes mellitus, thyroid disease, renal disease, autoimmune disease, heart disease, gestational hypertension, preeclampsia/eclampsia, gestational diabetes, cholestasis, SGA, suspected macrosomia, abnormal antenatal testing results, antenatal stillbirth, fetal anomaly, breech or other non-cephalic presentation, PROM, late-term or post-term pregnancy, uterine scar, placental abruption, placenta previa, and prolapse of the cord.
Each birth was assigned a weight with inverse probability weighting, taking into account the number of births in the same administrative region in hospitals of the same level, the total number of births in the prior year in the same hospital, and the number of records reviewed in the same hospital. The 2016 China Statistical Yearbook was used to determine the number of deliveries in each administrative region .
We used frequencies to describe induction rates for each maternal characteristic, medical condition, initial cervical assessment, and method of induction among women undergoing labor induction. Frequencies were calculated separately for nulliparous and multiparous women by using the PROC SURVEYFREQ procedure in SAS. Multivariable logistic regression was used to assess the association between medical conditions and cesarean delivery among women undergoing labor induction, by using the PROC SURVEYLOGISTIC procedure in SAS. Both procedures incorporated the sampling weight and the clustering of births within hospitals. We reported crude and adjusted odds ratios (ORs) with 95% confidence intervals (CIs) in nulliparous and multiparous women, controlling for maternal age, race, insurance status, education level, body mass index (BMI) at delivery, number of fetuses, fetal presentation, use of labor analgesia, hospital location, and hospital level. A weighted proportion of attempted mode of delivery, i.e., spontaneous labor, labor induction, cesarean delivery without indications, and cesarean delivery with indications, was calculated to reveal the differences between geographical regions. Linear regression analysis was performed to assess the association between the prelabor cesarean delivery and labor-induction rates in each hospital, adjusting for sampling weight, hospital level, and hospital location. The impacts of labor induction and prelabor cesarean delivery on maternal and neonatal outcomes were compared in low-risk women. SAS version 9.4 (SAS Institute Inc., Cary, NC) was used for all statistical analyses.