Associations of neonatal high birth weight with maternal pre-pregnancy body mass index and gestational weight gain: a case–control study in women from Chongqing, China

OBJECTIVES: To examine the associations of maternal pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) with neonatal high birth weight (HBW) in a sample of Chinese women living in southwest China. METHODS: A hospital-based case–control study was conducted in Chongqing, China. A total of 221 mothers who delivered HBW babies (>4.0 kg) were recruited as cases and 221 age-matched (2-year interval) mothers with normal birth weight babies (2.5–4.0 kg) were identified as controls. ORs were estimated using conditional logistic regression analysis. For the analysis, pre-pregnancy BMI was categorised as underweight/normal weight/overweight and obesity and GWG was categorised as inadequate/appropriate/excessive. RESULTS: Among the cases, mean pre-pregnancy BMI was 21.8±2.8 kg/m(2), mean GWG was 19.7±5.1 kg and mean neonatal birth weight was 4.2±0.2 kg. In the controls, the corresponding values were 21.1±3.1 kg/m(2), 16.4±5.0 kg and 3.3±0.4 kg, respectively. More cases than controls gained excessive weight during pregnancy (80.1% vs 48.4%, p<0.001). No significant association was found between pre-pregnancy BMI and HBW babies (OR=1.04, 95% CI 0.97 to 1.11; p>0.05). GWG was positively related to HBW after adjustment for gravidity, gestational age, newborns' gender and family income (OR=1.18, 95% CI 1.12 to 1.25; p<0.001). The adjusted OR of delivering HBW babies was 5.39 (95% CI 2.94 to 9.89; p<0.001) for excessive GWG versus appropriate GWG. This OR was strengthened among pre-pregnancy normal weight women (OR=10.27, 95% CI 3.20 to 32.95; p<0.001). CONCLUSIONS: Overall, the findings suggest a significantly positive association between GWG and HBW. However, pre-pregnancy BMI shows no independent relationship with HBW.