Preterm birth was defined as birth before 37 weeks’ gestation(10). Low birthweight (LBW) was defined as birth weight < 2,500 g(10) and very low birth weight (VLBW) was defined as birthweight < 1,500 g(10).
The controls were age-matched pregnant women with normal blood pressure who delivered next to the study one, on the same day. The ratio of study to control was 1:1.