Placental abruption in parents who were born small: registry-based cohort study.

OBJECTIVE: To assess whether parents who were born small for gestational age (below the 10th birthweight centile, SGA) have increased risk of severe or mild placental abruption. To assess whether a history of SGA in other family members modifies this intergenerational effect. DESIGN: Prospective population-based observational study. SETTING: The Medical Birth Registry of Norway. POPULATION: From 1967 to 2013, 785 333 mother-offspring pairs, 643 066 father-offspring pairs, 272 941 maternal tetrads (i.e. her offspring, sibling, and niece/nephew), and 265 505 paternal tetrads were identified. METHODS: Cohort study based on linked data from the Medical Birth Registry of Norway. MAIN OUTCOME MEASURES: Relative risk (RR) of severe placental abruption (preterm birth, birthweight below the 10th centile, or perinatal death) and mild placental abruption (other cases) in families with SGA. RESULTS: Mothers who were born SGA had increased risk of severe placental abruption (RR 1.5; 95% confidence interval, 95% CI 1.3-1.8), but not mild abruption. The paternal effects were weaker. The combined effect of SGA in the mother and her sibling on severe abruption was twofold (RR 2.4; 95% CI 1.7-3.3) compared with birthweight centiles ≥10 for both. Similarly, the effect of adding an SGA niece/nephew was twofold (RR 2.3; 95% CI 1.3-3.9), whereas the combined effect of SGA in the mother, her sibling and her niece/nephew was fourfold (RR 3.6; 95% CI 1.9-6.8). CONCLUSIONS: Women who were born SGA have an increased risk of severe placental abruption. The corresponding paternal effect was modest. A history of SGA in other family members increases the generational effect. TWEETABLE ABSTRACT: Women born small for gestational age have excess risk of placental abruption.