Background
Obesity in pregnancy is associated with a number of adverse outcomes. The effects of central versus general obesity in pregnancy have not been well established.

Aim
To compare subcutaneous fat thickness (SFT) with body mass index (BMI) as a marker for pregnancy outcomes.

Methods
A stratified retrospective cohort study was performed on 1200 pregnancies, selected from a total of 4862 nulliparous, nonsmoking women between 2006 and 2010. SFT was measured on routine ultrasound at 18–22 weeks gestation. BMI and SFT measurements were compared for estimating risks for obesity‐related pregnancy outcomes using logistic regression adjusted for maternal age.

Results
The median SFT was 18.2 mm (range 6.3–50.9 mm), the median BMI was 23.8 kg/m2 (range 15.2–52.5), and the correlation between SFT and BMI was 0.53. For every 5 mm increase in SFT and every 5 kg/m2 increase in BMI, the odds ratios for developing gestational diabetes mellitus were 1.40 (CI 1.22–1.61, P < 0.001) and 1.16 (CI 0.95–1.40, P = 0.1), for caesarean section 1.28 (CI 1.16–1.40, P < 0.001) and 1.16 (CI 1.05–1.28, P = 0.003), large for gestational age 1.28 (CI 1.16–1.47, P = 0.001) and 1.10 (CI 0.95–1.28, P = 0.16) and cumulative adverse obesity‐related pregnancy outcomes 1.16 (CI 1.10–1.28, P = 0.002) and 1.05 (CI 0.95–1.16, P = 0.45), respectively. Conclusion SFT at 18–22 weeks gestation is better than BMI as a marker for obesity‐related pregnancy outcomes. As SFT is considered a surrogate measure for visceral fat, these results suggest that central obesity is a stronger risk factor than general adiposity in pregnancy.