Outcome measures
The outcome measures were maternal and infant outcomes, mode of delivery, and gestational age at delivery of the new pregnancies. Maternal outcomes were recorded as uncomplicated, repeat complete rupture, partial rupture, peripartum hysterectomy, and abnormally invasive placenta. Infant outcomes were recorded as healthy, moderate asphyxia, severe asphyxia, admission to neonatal intensive care unit (NICU), and perinatal death (stillbirth and neonatal death). All were categorized into Yes or No.
Mode of delivery was grouped into elective CS, emergency prelabour CS, and vaginal delivery. Gestational age at delivery was grouped into weeks: <28, 28-32, 33-36, 37-38, and 39 weeks.
Peripartum hysterectomy was defined as surgical removal of the uterus at the time of delivery or up to 42 days postpartum, excluding hysterectomy because of cancer. Abnormally invasive placenta included all types of morbidly adherent placenta defined by histology, including accreta, increta, and percreta.
Stillbirth was defined as infant death before birth caused by asphyxia related to uterine rupture, and neonatal death was defined as death ≤7 days after birth. We defined severe asphyxia8using diagnostic ICD-10 code P21.0 (asphyxia with 1-minute Apgar score 0–3). We defined moderate asphyxia8using ICD-10 code P21.1 (asphyxia with 1-minute Apgar score 4–7). NICU admission was defined as admission due to prematurity. Healthy was defined as an infant without any complications and no admission to the NICU.
Characteristics of previous ruptures :
Characteristics of previous ruptures included place of rupture (within lower uterine segment [LS; reference] and outside LS), gestational age at rupture (< 37 weeks and ≥37 weeks [reference]), time of occurrence of rupture (before labour start and after labour start [reference]), detection time (during CS or postpartum after vaginal delivery/CS), and presence of perinatal death. In addition, the inter-delivery interval was included and defined as the time from complete rupture to new delivery (1 year, 2-3 years [reference], and ≥ 4 years).