Association between Maternal Origin, Pre-Pregnancy Body Mass Index and Caesarean Section: A Nation-Wide Registry Study

Aims: To explore the association between maternal origin and birthplace, and caesarean section (CS) by pre-pregnancy body mass index (BMI) and length of residence. Methods: We linked records from 118,459 primiparous women in the Medical Birth Registry of Norway between 2013 and 2017 with data from the National Population Register. We categorized pre-pregnancy BMI (kg/m(2)) into underweight (<18.5), normal weight (18.5–24.9) and overweight/obese (≥25). Multinomial regression analysis estimated crude and adjusted relative risk ratios (RRR) with 95% confidence intervals (CI) for emergency and elective CS. Results: Compared to normal weight women from Norway, women from Sub-Saharan Africa and Southeast Asia/Pacific had a decreased risk of elective CS (aRRR = 0.57, 95% CI 0.37–0.87 and aRRR = 0.56, 0.41–0.77, respectively). Overweight/obese women from Europe/Central Asia had the highest risk of elective CS (aRRR = 1.42, 1.09–1.86). Both normal weight and overweight/obese Sub-Saharan African women had the highest risks of emergency CS (aRRR = 2.61, 2.28-2.99; 2.18, 1.81-2.63, respectively). Compared to women from high-income countries, the risk of elective CS was increasing with a longer length of residence among European/Central Asian women. Newly arrived migrants from Sub-Saharan Africa had the highest risk of emergency CS. Conclusion: Women from Sub-Saharan Africa had more than two times the risk of emergency CS compared to women originating from Norway, regardless of pre-pregnancy BMI.