Population and setting
Data collection, data quality assurance procedures and standard
operating procedures used for the individual patient database are
reported
elseswhere.24Briefly, 150 variables (i.e., maternal sociodemographic characteristics,
risk factors, process indicators, maternal and neonatal outcomes) were
collected for each birth on two wards of the University Obstetric Unit
at De Soysa Teaching Hospital for Women, using a standardised two-page
form, and entered in real time in an electronic database. De Soysa is
the largest referral hospital for maternity care in Sri Lanka and all
deliveries occurring in these two wards from May 2015 to May 2019 were
entered in the database and considered for inclusion. Overall data
quality was routinely monitored with external independent random review
of 5% of forms and 5% of entered births to maintain an error rate in
data collection below 0.02%.24 Data were also
externally monitored for completeness and internal consistency at
roughly 4-month intervals.24
We included “low risk women” with singleton pregnancies and a foetus
in cephalic presentation whose delivery occurred between 40+0 and 41+6
GW. We excluded all cases with any maternal or foetal characteristics
which may have affected outcomes, such as: maternal obesity (Asian
criteria-based body mass index -BMI- more than
27.525), previous CS, macrosomia at ultrasonography
(defined as estimated birthweight exceeding the 90thcentile for gestational age), hypertension disorders during pregnancy
(e.g. pregestational or gestational hypertension, preeclampsia,
eclampsia, HELLP syndrome), chorioamnionitis, major foetal
malformations, intrauterine growth restriction at ultrasonography
(IUGR), small for gestational age (SGA), pre-gestational diabetes,
gestational diabetes with the need of drug therapy, maternal cardiac
disease, maternal hypothyroidism, polyhydramnios, oligohydramnios,
antepartum haemorrhage (APH), major placenta praevia, placental
accretism, severe anaemia (haemoglobin <7.0 g/dl) and other
foetal and maternal pathological conditions, i.e. systemic lupus
erythematosus, pre-pregnancy deep venous thrombosis, epilepsy, suspected
cephalo pelvic disproportion, recurrent infection, pancreatitis or
glomerulonephritis in pregnancy, chickenpox disease, chronic disease,
signs of potentially impaired
foetal wellbeing (non-reassuring or pathological cardiotocography,
reduced foetal movement, meconium stained amniotic fluid). We also
excluded macerated stillbirth from the IOL40 group, as these births are
always induced. All women with a reported indication for IOL suggesting
the presence of maternal or foetal characteristics described above, such
as diabetes, macrosomia at ultrasound, IUGR/SGA, were excluded from the
analysis.