Outcome measures
Obstetric complications—We defined pre-eclampsia as a diasto- lic blood pressure ≥ 90 mm Hg on two occasions at least four hours apart in the second half of pregnancy in a previously normotensive woman and proteinuria ( ≥ 300 mg/24 hours).17 In patients with pre-existing hypertension, pre-eclampsia was diagnosed when proteinuria occurred de novo in the second half of pregnancy.
Perinatal outcome—We divided congenital malformations into major and minor malformations. We classified a malformation as major if it was fatal, potentially life threatening, likely to lead to serious handicap or major cosmetic defect, or requiring major surgery. We classified chromosomal abnormalities as major malformations. We included fetuses of ≥ 24 weeks’ gestation, weighing ≥ 500 g, or both (n = 324) and therapeutic abortions due to congenital malformations or chromosomal abnormalities (n = 4). We defined perinatal mortality as fetal losses from 24 weeks of gestation, ≥ 500 g, or both, together with all postnatal deaths up to seven days after birth. We grouped birth weight by centiles according to the official Dutch growth charts, published in 1970,18 and according to a growth chart based on the 1998 Dutch perinatal database (including 181 000 deliveries).19 We defined macrosomia as birth weight above the 90th centile cor- rected for gestational age, sex, and parity. We defined severe macrosomia as birth weight above the 97.7th centile.
Neonatal outcome—We defined neonatal hypoglycaemia as blood glucose < 2.6 mmol/l and severe neonatal hypoglycaemia as blood glucose < 2.0 mmol/l.20 We defined infant respiratory distress syndrome according to Giedion et al and according to clinical symptoms of respiratory stress.21
We compared maternal and perinatal outcomes with national data from the 1998 Dutch perinatal database and with data from Statistics Netherlands.19 22–27 Information about pregnancy, delivery, and puerperium of pregnancies with a dura- tion of at least 16 completed weeks is collected in the Dutch perinatal database, which contains data on 91% of all deliveries.