The role of intervening pregnancy loss in the association between interpregnancy interval and adverse pregnancy outcomes

First published: 20 May 2022Abstract Objective: To investigate whether intervening miscarriages and induced abortions impact the associations between interpregnancy interval after a live birth and adverse pregnancy outcomes. Design: Population-based cohort study. Setting: Norway. Participants: A total of 165 617 births to 143 916 women between 2008 and 2016. Main outcome measures: We estimated adjusted relative risks for adverse pregnancy outcomes using log-binomial regression, first ignoring miscarriages and induced abortions in the interpregnancy interval estimation (conventional interpregnancy interval estimates) and subsequently accounting for intervening miscarriages or induced abortions (correct interpregnancy interval estimates). We then calculated the ratio of the two relative risks (ratio of ratios, RoR) as a measure of the difference. Results: The proportion of short interpregnancy interval (<6 months) was 4.0% in the conventional interpregnancy interval estimate and slightly increased to 4.6% in the correct interpregnancy interval estimate. For interpregnancy interval