Hypertension during pregnancy in South Australia, part 2: risk factors for adverse maternal and/or perinatal outcome - results of multivariable analysis.

OBJECTIVE: To identify factors associated with adverse pregnancy outcomes among women with hypertension during pregnancy.

DESIGN: A population-based retrospective multivariable analysis using the South Australian perinatal data collection.

METHODS: Perinatal data on 70,386 singleton births in 1998-2001 were used in multivariable analyses on three groups: all women combined, all hypertensive women and women with pregnancy hypertension only, in order to identify independent risk factors for requirement for level II/III care, preterm birth, small for gestational age (SGA) birth and maternal length of stay greater than 7 days.

RESULTS: The risks for the four morbidities were all increased among women with hypertension compared with normotensive women. Those with pre-existing hypertension had the lowest risk (with odds ratios (OR) 1.26-2.90). Pregnancy hypertension held the intermediate position (OR 1.52-5.70), while superimposed pre-eclampsia was associated with the highest risk (OR 2.00-8.75). Among women with hypertension, Aboriginality, older maternal age, nulliparity and pre-existing or gestational diabetes increased the risk for level II/III nursery care, preterm birth and prolonged hospital stay. Smokers had shorter stays, which may be related to their decreased risk of having a Caesarean section or operative vaginal delivery. Asian women, Aboriginal women, smokers and unemployed women had an increased risk for having an SGA baby, while women with pre-existing or gestational diabetes had a reduced risk.

CONCLUSIONS: Among hypertensive pregnant women, nulliparity, older maternal age, Aboriginality, unemployment and diabetes are independent risk factors for one or more major adverse pregnancy outcomes. Smoking does not always worsen the outcome for hypertensive women except for SGA births.