Objective We analysed the influence of body mass index (BMI) on caesarean section (CS) rates when BMI was based on the accurate measurement rather than self-reporting of maternal weight and height.

Study design We enrolled women at their convenience after ultrasound confirmed an ongoing pregnancy in the first trimester. Weight and height were measured and BMI calculated. Clinical and demographic details were recorded prospectively.

Results Out of 2000 women enrolled, 1927 subsequently delivered in our hospital. There were 50.4% primigravidas and 49.6% multigravidas. The overall CS rate was 21.2%. The incidence of maternal obesity was 17.3%.

The CS rate was almost twice as high in obese women compared with women in the normal BMI category. There was a higher rate of emergency sections in obese primigravidas (p<0.005) and a higher rate of elective sections in obese multigravidas (p<0.001).

In obese primigravidas a CS was required in 20.6% for fetal distress compared with 9.8% in the normal BMI category (p=0.005). This may be due to a higher rate of induction of labour in these women. 17.2% of obese multigravidas had an elective repeat CS compared with 7.7% in the normal weight category.

Conclusion Our results suggest that in obese women induction of labour in primigravidas and VBAC rates in multigravidas need further review. The increased CS rate in obese women was less than studies where BMI was based on self-reporting, showing that self-reporting exaggerates the risks of obesity.