Maternal origin matters: Country of birth as a risk factor for obstetric anal sphincter injuries

Obstetric anal sphincter injuries (OASIS) are severe complications to vaginal births with potential long-term consequences. Maternal origin has been proposed to affect the overall risk, but the association and underlying explanation are uncertain. The objective was to assess the association between maternal country of birth and OASIS.

A Swedish nationwide cohort study including singleton term vaginal births during 2005-2016. Data were extracted from the Swedish Medical Birth Registry and Statistics Sweden. Modified Poisson regression analyses were performed to obtain crude and adjusted risk ratios (RRs). Adjustments were made in four cumulative steps. Sub-analyses were performed to investigate the risk of OASIS associated with female genital circumcision (FGC).

In all, 988 804 births were included. The rate of OASIS in Swedish-born women was 3.5%. Women from East/Southeast Asia had an increased risk of OASIS (adjusted RR [aRR] 1.71, 95% confidence interval [CI] 1.60-1.83), as did women born in Sub-Saharan Africa (aRR 1.60, 95% CI 1.49-1.72). The risk remained significantly increased also after adjustment for maternal height. By contrast, women from South/Central America had a decreased risk of OASIS (aRR 0.65, 95% CI 0.56-0.76). FGC was associated with an increased risk of OASIS (aRR 3.05, 95% CI 2.60-3.58). Episiotomy appeared to have an overall protective effect (aRR 0.95, 95% CI 0.92-0.98), but not significantly more protective among women with female genital mutilation.

Country of birth plays an important role in the risk of OASIS. Women from East/Southeast Asia and Sub-Saharan Africa are at significantly increased risk as compared with Swedish-born women, whereas women from South/Central America are at lower risk. FGC is also a significant risk factor for OASIS.