Objective: To determine if the influence of preeclampsia on birth size varies with clinical manifestations of the disease, and to evaluate whether maternal factors, such as smoking, modify the effect of preeclampsia on fetal growth.
Methods: Among 12,804 deliveries in a population of approximately 239,000 over a 3-year period, 307 live singleton infants were born after preeclamptic pregnancies. We compared those with a sample of 619 control infants. Preeclampsia was defined as increased diastolic blood pressure (BP) (increase of at least 25 mmHg to at least 90 mmHg) and proteinuria after 20 weeks' gestation. Clinical manifestations were classified according to BP and proteinuria into subgroups of mild, moderate, or severe (including cases with eclampsia and hemolysis, elevated liver enzymes, low platelets [HELLP] syndrome) preeclampsia, and according to gestational age at onset, as early or late preeclampsia. Birth size was expressed as the ratio between observed and expected birth weights, and infants smaller than two standard deviations from expected birth weights were classified as small for gestational age (SGA).
Results: Preeclampsia was associated with a 5% (95% confidence interval [CI] 3%, 6%) reduction in birth weight. In severe preeclampsia, the reduction was 12% (9%, 15%), and in early-onset disease, birth weight was 23% (18%, 29%) lower than expected. The risk of SGA was four times higher (relative risk [RR] = 4.2; 95% CI 2.2, 8.0) in infants born after preeclampsia than in control pregnancies. Among nulliparas, preeclampsia was associated with a nearly threefold higher risk of SGA (RR = 2.8; 1.2, 5.9), and among paras, the risk of SGA was particularly high after recurrent preeclampsia (RR = 12.3; 3.9, 39.2). In relation to preeclampsia and maternal smoking, the results indicated that each factor might contribute to reduced growth in an additive manner.
Conclusion: Severe and early-onset preeclampsia were associated with significant fetal growth restriction. The risk of having an SGA infant was dramatically higher in women with recurrent preeclampsia. Birth weight reduction related to maternal smoking appeared to be added to that caused by preeclampsia, suggesting that there is no synergy between smoking and preeclampsia on growth restriction.