Estimated reductions in provider-initiated preterm births and hospital length of stay under a universal acetylsalicylic acid prophylaxis strategy: a retrospective cohort study.

BACKGROUND: Hypertensive disorders, especially preeclampsia, are the leading reason for provider-initiated preterm birth. We estimated how universal acetylsalicylic acid (ASA) prophylaxis might reduce rates of provider-initiated preterm birth associated with preeclampsia and intrauterine growth restriction, which are related conditions.

METHODS: We performed a cohort study of singleton hospital births in 2013 in Canada, excluding Quebec. We estimated the proportion of term births and provider-initiated preterm births affected by preeclampsia and/or intrauterine growth restriction, and the corresponding mean maternal and newborn hospital length of stay. We projected the potential number of cases reduced and corresponding hospital length of stay if ASA prophylaxis lowered cases of preeclampsia and intrauterine growth restriction by a relative risk reduction (RRR) of 10% (lowest) or 53% (highest), as suggested by randomized clinical trials.

RESULTS: Of the 269 303 singleton live births and stillbirths in our cohort, 4495 (1.7%) were provider-initiated preterm births. Of the 4495, 1512 (33.6%) had a diagnosis of preeclampsia and/or intrauterine growth restriction. The mean maternal length of stay was 2.0 (95% confidence interval [CI] 2.0-2.0) days among term births unaffected by either condition and 7.3 (95% CI 6.1-8.6) days among provider-initiated preterm births with both conditions. The corresponding values for mean newborn length of stay were 1.9 (95% CI 1.8-1.9) days and 21.8 (95% CI 17.4-26.2) days. If ASA conferred a 53% RRR against preeclampsia and/or intrauterine growth restriction, 3365 maternal and 11 591 newborn days in hospital would be averted. If ASA conferred a 10% RRR, 635 maternal and 2187 newborn days in hospital would be averted.

INTERPRETATION: A universal ASA prophylaxis strategy could substantially reduce the burden of long maternal and newborn hospital stays associated with provider-initiated preterm birth. However, until there is compelling evidence that administration of ASA to all, or most, pregnant women reduces the risk of preeclampsia and/or intrauterine growth restriction, clinicians should continue to follow current clinical practice guidelines.