Objective  To examine the effect of fertility policy change on maternal characteristics and birth defect incidence in Lanzhou city.

  Methods  The data on 6 826 pairs of maternal-infant with birth defect were extracted from datasets of birth defect surveillance for years of 2010 – 2019 in Lanzhou city, Gansu province; then the data were divided into three sub-datasets for the periods of January 2010 – March 2014, April 2014 – December 2015, and January 2016 – December 2019 according to the implementation time of "one child", "separate two-child", and "universal two-child" fertility policy in Gansu province. The maternal characteristics, child characteristics and the incidence of major birth defects for the three periods were analyzed and compared.

  Results   The number of the maternal-infant pairs for the three periods were 1 511, 1 174 and 4 141, respectively. During the period with the implementation of universal two-child policy, the proportions of pregnant women having higher education/income, at elder age, being multipara, and with the gestational week of less than 28 weeks increased significantly (P < 0.05 for all), but the average gestational age and gestational weight of the infants decreased significantly compared to those during other two periods (both P < 0.05). After adjusting for potential confounding variables, multivariate logistic regression analysis revealed that the infants delivered during the period with the implementation of universal two-child policy were at an increased risk congenital heart disease (odds ratio OR = 4.228), cleft lips (OR = 1.207), polydactyly (OR = 2.252), syndactyly (OR = 1.788), clubfoot (OR = 1.602) and Down′s syndrome (OR = 3.065) but at a decreased risk of multiple defects (OR = 0.147) in comparison with the infants delivered during the other two periods.

  Conclusion  In Lanzhou city during the period with the implementation of universal two-child policy, the proportion of pregnant women at elder age and being multipara increased and the risk of birth defects increased among the infants delivered.