Change in paternity: a risk factor for preeclampsia in multiparas.

Preeclampsia, a hypertensive disorder of pregnancy, is hypothesized to be a maternal immunologic response to foreign fetal antigen derived from the father's sperm. This response may be reduced by prolonged exposure to father's antigen, such as through a prior pregnancy, which may explain why multiparas are typically at lower risk for preeclampsia than nulliparas. Since multiparas with new partners are presented with a new set of paternal antigen, we hypothesize that they would have the same elevated risk for preeclampsia and gestational hypertension as nulliparas, compared with multiparas with no change in partner. We studied 5,068 nulliparas and 5,800 multiparas, 573 of whom had new partners, selected from the Child Health and Development Studies cohort (Oakland, CA, 1959-1967). Preeclampsia was diagnosed in 3.2% of nulliparas, 3.0% of multiparas with changed paternity, and 1.9% of multiparas with no change. Compared with multiparas with no change, the adjusted odds ratio for preeclampsia among nulliparas was 2.5 [95% confidence interval (CI) = 1.8-3.5]; among multiparas with new partners, the adjusted odds ratio for preeclampsia was 1.4 (95% CI = 0.8-2.4). There was a similar pattern of results for gestational hypertension. The adjusted attributable risk of preeclampsia in multiparas associated with a change in paternity was 29%. Although these findings in part support the immunologic theory of preeclampsia, they also suggest that a subsequent pregnancy with any partner is associated with a reduced risk for preeclampsia.