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Recurrence risk of preeclampsia in twin and singleton pregnancies

The etiology of preeclampsia is unknown. The relatively high risk of recurrence of preeclampsia in subsequent pregnancies to the same mother suggests a genetic basis for the disease, but the mode of inheritance is uncertain. We compare the risk of preeclampsia in second pregnancies for mothers whose first preeclamptic pregnancy was either a singleton or a twin pregnancy. The crude and adjusted recurrence risks of preeclampsia in twin and singleton pregnancies were estimated in a population‐based register including the first and second pregnancies of 550,218 women registered in the Medical Birth Registry of Norway, 1967–1998. The recurrence risk of preeclampsia in second pregnancy for women with a singleton pregnancy with preeclampsia the first time was 14.1% (95% CI: 13.6–14.6). For women with a first time twin pregnancy the recurrence risk was lower, 6.8% (CI: 4.3–10.1), P < 0.001. Thus, the crude excess risk for recurrent preeclampsia was 7.3% (95% CI: 4.5–10.0) in women with a first time singleton as compared to women with a first time twin pregnancy. The recurrence risk of preeclampsia is lower when the first pregnancy was a twin as compared to a singleton pregnancy. This observation is consistent with a polygenic liability model. © 2003 Wiley‐Liss, Inc.