Occurrence of Placental Abruption in Relatives

Abstract

Both genetic and environmental factors may influence the incidence and rate of recurrence of placental abruption in women and their families. The influence of heredity on the severity of recurrent disease is unknown. This population-based prospective observational study investigated the effect of heritability on rates of recurrence of placental abruption and severity of recurrence in the same woman or her sister and the partner of her brother. From 1967 to 2005, data obtained from the Medical Birth Registry of Norway on 2,274,850 births identified 377,902 sisters with 767,395 pregnancies and 168,142 families with 2 to 10 sisters, and 346,385 brothers with 717,604 pregnancies of their partners. Multiple births were excluded. Severe disease was defined as cases of placental abruption with birth before 37 weeks' gestation, and birth weight below 2500 gm or perinatal death. Other cases were defined as mild. Multilevel logistic regression models were used to calculate odds ratios. The likelihood of recurrence of severe disease in women who initially had severe placental abruption was higher in comparison to those with initial mild disease; the respective adjusted odds ratios (aOR) were 11.5 (95% confidence interval [CI], 9.1-14.6) and 6.5 (95% CI, 4.2-10.3). These ratios compare to risks of 0.2 and 0.3 in women without a history of placental abruption. Severe placental abruption was associated consistently with significantly higher recurrence rates between sisters compared to mild placental abruption (aOR: severe 1.7 and 2.1 vs. mild 0.8 and 1.1 ). The heritability estimated between sisters of severe placental abruption was 16%. After an initial severe placental abruption, no excess recurrence of placental abruption was observed between sisters and the partners of their brothers, or from brothers' partners to their sisters. Following a second placental abruption (mild or severe) and a second severe abruption in the same woman, the risk of placental abruption in a subsequent pregnancy was very high; the odds ratios were 38.7 (19%, 11/58) and 50.1 (24%, 10/42), respectively. The investigators conclude from these findings that pregnancies following a second placental abruption in women who have had severe placental abruption should be considered very high-risk and monitored accordingly.