Introduction There has been a relentless rise in the caesarean section (CS) rate in Ireland. The reasons for this increase are multifactorial and complex. This prospective observational study examined whether the variation in CS rates in European women can be explained by differences in maternal adiposity.

Study design Women were recruited after first trimester sonographic confirmation of an ongoing singleton pregnancy. Maternal adiposity was assessed indirectly by Body Mass Index (BMI) and directly by bioelectrical impedance analysis (BIA). Irish women were compared with other women born in the 14 countries who joined the EU before 2004, and with women born in the countries who joined following enlargement in 2004(EU 12).

Results Of the 2811 women enrolled, 2235 women were born in Ireland, 100 in the EU 14 and 476 in the EU 12 countries. Based on a BMI >29.9 kg/m2, maternal obesity was higher in Irish (19.8%) and EU 14(19.0%) women compared with EU 12 women (9.5%), p< 0.001. BIA confirmed increased adiposity in Irish and EU 14 women compared with EU 12 women. After multivariate analysis was performed controlling for age, socioeconomic group, induction of labour and birth weight, the increased adiposity in Irish women was associated with an increase in emergency CS rate in primigravidas (p<0.001).

Conclusion We found variation in CS rates in primigravidas based on the mother's country of birth, which was associated with maternal adiposity. Differences in maternal adiposity between nationalities may be hereditary in origin, but may be related to prepregnancy lifestyle.