Analysis of trends of birth weight, and incidence of adverse birth outcomes and relevant factors from 2002 to 2015

Objective To describe the trends of birthweight from 2002 to 2015, and analyze the incidence of adverse birth outcomes and to explore their relevant factors. Methods Datasets were obtained from decoded Electronic medical recorder system (EMRS) of Zhoushan, trends of birthweight were described, incidence of adverse birth outcomes were analyzed. Multivariate Logistic regression was used to analyze relevant factors. Results Mean birth weight of 37 141 newborns were (3 388±462) g, and incidence of low birth weight, macrosomia, preterm birth were 2.34%, 9.42% and 3.61%, respectively. Girls had higher risk of low birth weight than boys. Pre-pregnancy underweight or overweight, high risk pregnancy (OR=1.80, 95% CI:1.42-2.28) were risk factors of low birth weight. High levels of maternal education reduced the risk of low birth weight; girls had lower risk of macrosomia than boys. Pre-pregnancy overweight and obese increased the risk of macrosomia. Born in summer or fall, maternal age <25 and pre-pregnancy underweight reduced the risk of macrosomia. Girls had lower risk of preterm birth than boys. Maternal age <25 reduced the risk of preterm, maternal age >30 (OR=1.38, 95% CI:1.19-1.60), born in winter (OR=1.24, 95% CI:1.06-1.45), pre-pregnancy overweight or obese and high risk pregnancy (OR=1.95, 95% CI:1.66-2.29) increased risk of preterm birth. Conclusions During 2002-2015, mean birth weight tends to decrease, incidence of low birth weight and preterm birth tend to increase. Incidence of macrosomia or low birth weight and preterm birth were relevant with newborn's gender, maternal age, pre-pregnancy body mass index (BMI) and high risk pregnancy.