Introduction Obesity is a well established risk factor for adverse pregnancy outcomes. We investigated whether maternal percentage body fat (PBF) and visceral fat area (VFA) are better prognostic indicators for large-for-gestational age (LGA) babies compared with maternal body mass index (BMI).

Method We prospectively analysed 100 consecutive women attending a weight management clinic with booking BMI> 35 and no known diabetes. PBF and VFA were assessed by a body composition analyser (InBody⁷²⁰) at booking and at 36 weeks gestation. Birth weight centiles were derived from standardised centile calculators.

Results At booking, women (median [range]) aged 30 (26-33) years, BMI 36.5 (38.5-42), 80% Caucasian, 12% Asian, 8 % African, had PBF(%) of 50.5 (47.8-51.9) reference range < 28% and VFA (units) of 189.6 (164.9-210.6) reference range <100. During pregnancy, the median weight change (ΔWt) was 6.5 [3.8-10.2] kg. The proportion of LGA babies for the whole cohort was 66%. No significant correlation was found between maternal BMI, PBF, VFA, ΔWt or changes in body composition during pregnancy and birth weight centiles. There was no significant difference in the number of LGA babies in the subgroup who gained minimal weight (<5kg) compared with the rest of the group. (72.2% vs 62.5%, NS).

Conclusion Obese women have increased PBF and VFA and high rate of LGA babies. Although we found no significant correlation between maternal body composition and birth centiles in obese women, further studies are needed to ascertain whether neonatal body composition is better correlated.