, Volume 283, Issue 1, pp 65-70
Date: 22 Nov 2009

Effect of pre-pregnancy body mass index on adverse pregnancy outcome in north of China

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To investigate the effect of pre-pregnancy BMI on adverse maternal and neonatal outcomes in pregnancy women of northern China.


We conducted a retrospective population-based cohort study of 5,047 singleton nulliparous pregnancies. The subjects were categorized into four groups by BMI-underweight (BMI < 18.5 kg/m2), normal (BMI 18.5–24 kg/m2), overweight (BMI 24–28 kg/m2) and obese (BMI ≥ 28 kg/m2). Logistic regression was used to adjust the potential confounder. Maternal and neonatal outcomes were evaluated with relative risks and 95% confidence intervals.


11.5, 63.4, 18.3, and 6.8% of the subjects were underweight, normal BMI, overweight and obese, respectively. Compared with women of normal BMI, the risk of the following outcomes was significantly increased in overweight and obese women and expressed as [adjusted RR (95% confidence interval)] respectively: pre-eclampsia [2.99 (2.21–4.06), 5.68 (3.97–8.11)]; gestational diabetes [2.49 (1.82–3.39), 4.35 (3.00–6.31)]; premature rupture of the membranes [1.64 (1.20–2.23), 1.73 (1.11–2.72)]; abruption placentae [1.84 (1.19–2.87), 2.79 (1.60–4.83)]; cesarian section [1.47 (1.27–1.70), 2.51 (1.97–3.20)]; postpartum hemorrhage [2.31 (1.51–3.54), 3.73 (2.37–5.04)]; perineal rupture [2.89 (1.44–5.81), 3.36 (1.55–7.30)]; large-for-gestational age [1.46 (1.02–2.08), 1.91 (1.17–3.10)]. However, anemia (2.54, 1.15–5.63), small-for-gestational age (1.67, 1.07–2.61) were significantly more common in the underweight group.


The prevalence of overweight and obesity in women of northern China is much lower than in the Caucasian population or Chinese in Hong Kong. The increased maternal BMI is associated with many adverse pregnancy outcomes and its risk increases with the degree of obesity. Maternal underweight has a protective effect although increases the risk of having small-for-gestational age baby and anemia.