Outcomes
The obstetric outcomes of interest were pregnancy complications, placental abnormalities, PPH and adverse birth outcomes. Pregnancy complications were extracted from medical records and mainly included gestational diabetes mellitus (GDM), gestational hypertension (GH), preeclampsia (PE) and intrahepatic cholestasis of pregnancy (ICP). GDM was diagnosed based on a standard 75 g oral glucose tolerance test (OGTT) according to the recommendations of the International Association of Diabetes and Pregnancy Study Groups (IADPSG) 26. GH and PE were diagnosed according to the guidelines for the diagnosis and management of hypertensive disorders in pregnancy 27. ICP was diagnosed according to the guidelines of the Chinese Medical Association of Obstetrics and Gynecology 28.
Placental abnormalities and PPH were also extracted from the medical records. Placental abnormalities comprised low-lying placenta, placenta previa and placenta accreta spectrum, including placenta accrete/increta/percreta. PPH was defined as blood loss ≥ 500 ml for vaginal delivery or blood loss ≥ 1000 mL for cesarean section. This definition was based on guidelines from the Chinese Society of Obstetrics and Gynecology and Chinese Medical Association29. Additionally, hemostatic therapies that referred women receiving Bakri balloon tamponade (BBT) or surgical management (vascular ligation and uterine compression sutures) for preventing PPH were also extracted.
Adverse birth outcomes, including preterm birth (PTB), cervical insufficiency, small for gestational age (SGA) and macrosomia, were extracted from medical records or newborn birth records. PTB was defined as a live birth before 37 completed weeks of gestation in accordance with the World Health Organization (WHO) definitions30. Then, PTB was categorized into three clinical subtypes: spontaneous PTB, preterm premature rupture of membranes (PPROM) and iatrogenic preterm birth. Iatrogenic PTB was defined as either induction or cesarean section before the onset of labor31,32. Additionally, the cervical cerclage rate, which is based on the indication of a history of abortion with painless cervical dilation or progressive shortening of the cervical lenth in this pregnancy in the second trimester, was also extracted and reflected cervical insufficiency to some extent 33. SGA was defined as newborns with birth weight below the 10th percentile for gestational age.