Can Drug Effects Explain the Recent Temporal Increase in Atonic Postpartum Haemorrhage?

Background: Rates of postpartum haemorrhage and atonic postpartum haemorrhage have increased in several high-income countries. We carried out a study to examine if drug use in pregnancy, or drug and other interactions, explained this increase in postpartum haemorrhage. Methods: The linked administrative and hospital databases of the Québec Pregnancy Cohort were used to define a cohort of pregnant women in Québec, Canada, from 1998 to 2009 (n = 138 704). Case–control studies on any postpartum haemorrhage and atonic postpartum haemorrhage were carried out within this population, with up to five controls randomly selected for each case after matching on index date and hospital of delivery (incidence density sampling). Conditional logistic regression was used to estimate the effects of drug use on postpartum haemorrhage and atonic postpartum haemorrhage. Results: There was an unexpected non-linear, declining temporal pattern in postpartum haemorrhage and atonic postpartum haemorrhage between 1998 and 2009. Use of antidepressants (mainly selective serotonin reuptake inhibitors) was associated with higher rates of postpartum haemorrhage [adjusted rate ratio (aRR) 1.48, 95% confidence interval (CI) 1.23, 1.77] and atonic postpartum haemorrhage [aRR 1.40, 95% CI 1.13, 1.74]. Thrombocytopenia was also associated with higher rates of postpartum haemorrhage [aRR 1.52, 95% CI 1.16, 2.00]. There were no statistically significant drug interactions. Adjustment for maternal factors and drug use had little effect on temporal trends in postpartum haemorrhage and atonic postpartum haemorrhage. Conclusions: Although antidepressant use and thrombocytopenia were associated with higher rates of atonic postpartum haemorrhage, antidepressant and other drug use did not explain temporal trends in postpartum haemorrhage.