Social disparity affects the incidence of placental abruption among multiparous but not nulliparous women: a register-based analysis of 1,162,126 singleton births.

OBJECTIVES: To identify risk factors for placental abruption and to evaluate associations between adverse perinatal outcomes and placental abruption stratified by parity among women with singleton births from 1991 to 2010 in Finland.

STUDY DESIGN: A retrospective population-based case-control study of singleton births in Finland from 1991 to 2010 (n=1,162,126 from the Finnish Medical Birth Register). We modelled the group-specific risk factors for placental abruption in unadjusted and adjusted models.

RESULTS: In total 3.5 and 3.7 per 1000 nulliparous and multiparous women, respectively, were affected by placental abruption. The recurrence rate was 8.6 per 1000 births. The adjusted risk for placental abruption increased in pregnancies characterised by advanced maternal age, low birth weight, smoking, major congenital anomaly, preeclampsia and male foetal sex in both parity groups. In vitro fertilisation increased the risk only in nulliparae whereas anaemia, a prior caesarean section and the lowest socioeconomic status increased the risk in multiparae. Births affected by placental abruption were associated with an increased admission for neonatal intensive care, preterm birth, low birth weight (<2500 g), small for gestational age infants, low Apgar scores, and low newborn umbilical vein pH (<7.15). Placental abruption resulted in increased risks of stillbirth and early neonatal death in both parity groups.

CONCLUSIONS: The burden of placental abruption is equal in nulliparae and multiparae, but risk factors vary substantially. Social disparity only affects the incidence of placental abruption among multiparous women, indicating that factors related to lifestyle and health behaviour have different effects on the parity groups.