Chronic hypertension and risk of placental abruption: is the association modified by ischemic placental disease?

OBJECTIVE: The purpose of this study was to evaluate whether the increased risk of placental abruption among women with chronic hypertension is modified by ischemic placental disease, specifically pregnancy-induced hypertension (PIH) and fetal growth restriction (FGR). STUDY DESIGN: We used the US linked natality and fetal death data files (1995-2002) and restricted the analysis to women who had a singleton birth at >= 22 weeks of gestation and to fetuses who weighed >= 500 g (n = 30,189,949). Fetal growth was defined both on a continuum ( < 1, 1-2, 3-4, 5-9, 10-19,..., >= 90) and as birthweight of < 10th percentile for gestational age ( FGR) or birthweight of > 90th percentile ( large for gestational age [LGA]). All analyses were adjusted for potential confounding factors through multivariable logistic regression. RESULTS: Rates of abruption among women with and without chronic hypertension were 15.6 and 5.8 per 1000 pregnancies, respectively ( relative risk [RR], 2.4; 95% CI, 2.3, 2.5). In comparison with normotensive women with appropriately grown babies (ie, 10th-90th percentile), the association between chronic hypertension and abruption was modified in the presence of FGR (RR, 3.8; 95% CI, 3.6, 4.1) and PIH (RR, 7.7; 95% CI, 6.6, 8.9). However, the highest risk was seen among women with chronic hypertension, PIH, and LGA (RR, 9.0; 95% CI, 7.2, 11.3). A dose-response relationship was observed between the risk of abruption and fetal growth ( assessed on a continuum), with the risk being lowest among LGA babies. CONCLUSION: The association between chronic hypertension and abruption is strong; ischemic placental disease ( PIH and FGR) modified this relationship. These findings suggest an etiologic relationship between abruption and chronic placental disease. Chronic hypertension, if associated with LGA, is not associated with abruption; however, chronic hypertension with superimposed PIH accompanied by LGA is associated with significantly increased risk.