Increased risk of adverse maternal pregnancy outcomes among undocumented migrants in Norway.

Background: Migrants are known to have an increased risk for adverse complications during delivery. However, it is not known whether undocumented migrants have a different risk profile compared to documented migrants and non-migrants. Better knowledge about undocumented migrants' reproductive outcomes is crucial to enable targeted preventive interventions. Method: We performed a historical register-based population study based on numbers from the Medical Birth Registry of Norway (MBRN) from 1999 to 2020. Women aged 18-49 years with singleton births were included, in total 1,247,537 births. Legal status, i.e., undocumented migrants (without a Norwegian identity number), documented migrants (with a Norwegian identity number and born abroad) and non-migrants (with a Norwegian identity number and born in Norway), was used as the exposure. We used logistic regression to estimate the association between legal status and adverse maternal birth outcomes. Results: In total 5856 undocumented migrant women gave birth during the study period, representing 0.5 % of all births in Norway. Undocumented migrants had an odds ratio (OR) of 1.39 (95 % Confidence Interval (CI) 1.28-1.50) for an acute CS and OR=0.86 (95 % CI 0.76-0.98) for a planned CS, both compared to non-migrants. Similarly, the OR for severe postpartum haemorrhage (PPH) was =1.22 (95 % CI 1.03-1.43) and OR=0.69 (95 % CI=0.56-0.85) for anal sphincter injury. None of the results were significantly different when documented migrants were used as the reference group. Conclusion: Undocumented migrants have an increased risk of adverse maternal birth complications compared to non-migrants, but not different from documented migrants. This indicates that for maternal birth complications, factors concerning migration may affect the risk profile to a larger degree than legal status.