Objective: Fetal growth during pregnancy may be affected by the metabolic activity and distribution of fat stores in women. This study investigates the association between waist to hip ratio (WHR) as a measure of the distribution of adiposity in primiparous mothers living in Avon, England, and macrosomia in their offspring.

Design: Prospective historical cohort study.

Setting: The Avon Longitudinal Study of Parents and Children (ALSPAC) prospective cohort study in Avon, UK.

Population: A cohort of 3083 primiparous women with a term singleton delivery with expected dates of delivery from 1 April 1991 to 31 December 1992.

Methods: The distribution of WHR was categorised into quartiles. We compared the second, third and fourth quartiles against the first (reference) quartile with respect to whether the mother delivered a macrosomic newborn. We controlled for maternal age, gestational age, body mass index (BMI), marital status and racial group using multivariate logistic regression.

Main outcome measures: Macrosomia defined in three ways: birthweight ≥ 4000 g; birthweight ≥ 4500 g; large for gestational age (LGA: ≥ 95th percentile of birth weight adjusted for sex and gestational age).

Results: Waist to hip ratios in the third and fourth quartiles were associated with a higher odds of delivering a macrosomic infant, defined as a birthweight ≥ 4000 g (third quartile, OR 1.59, 95% CI 1.12-2.26; fourth quartile, OR 1.69, 95% CI 1.18-2.42) or as LGA (≥95th percentile of the cohort; third quartile, OR 1.77, 95% CI 1.10-2.85; fourth quartile, OR 1.78, 95% CI 1.09-2.91). When defined as a birthweight ≥ 4500 g, the fourth quartile was associated with increased odds of macrosomia (OR 2.74, 95% CI 1.05-7.16). Odds ratios after adjustment for confounding factors followed a similar pattern.

Conclusion: Independent of confounding factors, women with increased WHRs were significantly more likely to give birth to macrosomic newborns.