Changing risk factors for placental abruption: A case crossover study using routinely collected data from Finland, Malta and Aberdeen.

OBJECTIVE To evaluate the effects of changes in risk factors between the first two pregnancies on the occurrence of placental abruption (PA) in the same woman. METHODS Routinely collected obstetric data from Aberdeen Maternity and Neonatal Databank, the Maltese National Obstetric Information System and the Finnish Medical Birth Register were aggregated. Records of the first two singleton pregnancies from women who had PA in one pregnancy but not the other, were identified from this pooled dataset. A case-crossover study design was used; cases were pregnancies with abruption and matched controls were pregnancies without abruption in the same woman. Conditional logistic regression was used to investigate changes in risk factors for placental abruption in pregnancies with and without abruption. RESULTS A total of 2,991 women were included in the study. Of these 1,506 (50.4%) had PA in their first pregnancy and 1,485 (49.6%) in a second pregnancy. Pregnancies complicated by preeclampsia {194 (6.5%) versus 115 (3.8%) adj OR 1.69; (95% CI 1.23-2.33)}, antepartum haemorrhage of unknown origin {556 (18.6%) versus 69 (2.3%) adjOR 27.05; 95% CI 16.61-44.03)} and placenta praevia {80 (2.7%) versus 21 (0.7%) (adjOR 3.05; 95% CI 1.74-5.36)} were associated with PA. Compared to 20 to 25 years, maternal age of 35-39 years {365 (12.2) versus 323 (10.8) (adjOR 1.32; 95% CI 1.01-1.73) and single marital status (adjOR 1.36; 95% CI 1.04-1.76) were independently associated with PA. Maternal smoking, BMI and fetal gender were not associated with PA. CONCLUSION Advanced maternal age, pregnancies complicated with unexplained bleeding in pregnancy, placenta praevia and preeclampsia were independently associated with a higher risk of placental abruption.