Objective  To investigate the association between maternal body mass index (BMI), pregnancy history and birthweight of offspring including low birthweight, macrosomia, small-for-gestational-age (SGA) and large-for-gestational-age (LGA) in Jiashan county of Zhejiang province.

  Methods  We recruited 919 pairs of women and their singleton neonates from the participants of National Free Preconception Health Examination Project (NFPHEP) conducted in Jiashan county of Zhejiang province in 2014 and 2015. Relevant information were extracted from the dataset of NFPHEP. Chi-square test, linear regression, and logistic regression model were applied in statistics analyses.

  Results  Of all the pregnant women, 21.00% (193) were overweight/obesity and 12.73% (117) were lean. For all the neonates, the mean birthweight was 3 339.90 ± 429.98 grams and the number of low birthweight, macrosomia, SGA, and LGA were 28, 57, 48, and 95, respectively. Linear regression analysis indicated that the neonates born to lean mothers had a birthweight of 65.44 (95% confidence interval 95% CI: – 130.57 – – 0.31) grams lower than that of the neonates born to mothers with normal weight significantly (t = – 1.97, P < 0.05) and the difference was much larger between the two groups of the neonates born to mothers with the education of senior high school or lower (β = – 148.05, 95% CI = – 286.36 – – 9.73)(t = – 2.11, P < 0.05). The overweight/obesity pregnant women had a 2.2 (95% CI: 1.08 – 4.44)-fold risk of to give a birth to a macrosomia and the risk was much higher for the overweight/obesity pregnant women more than 30 years old and with the education of senior high school or lower.

  Conclusion  Maternal BMI before pregnancy is associated with the birthweight in offspring. The pre-pregnancy overweight/obese women have an increased risk of to give a birth to a macrosomia and the risk is modified by maternal age, education and pregnancy history of the women.