Objective To investigate incidence rates of birth defects and diagnosed defect composition during pregnancy and different time period after birth, in order to explore more appropriate time period of birth defects monitoring. Methods The population-based surveillance data were retrived from reginal birth defects monitoring network, where all defects cases reported within 13 weeks of pregnancy to 2 years after birth were selected from 23 054 pregnant women who gave birth within 2010 to 2015 in Jiangbei district, Ningbo city.The incidence rates, the diagonozed defect types and the diagnosed time were descriptively analyzed. Results Totally 1 040 cases of birth defects were found from 2010 to 2015 for all registed pregnant women in the study area.From early pregnancy to 2 years after delivery, the cumulative reporting rate of birth defects was 4.51%, and there existed a year-by-year increasing trend.The incidences rate of birth defects was significantly higher in those of stillbirths.Congenital heart disease ranked the first in all types of birth defects.Calculated by different time (age) point of diagnose, the incidence rate of congenital heart disease was 2.7% from early pregnancy to 7 days after birth, 3.61% before 42 days after birth, 4.42% before 1 year old, and 4.51% before 2 years old.The detection rate of birth defects from gestation age of 13 weeks to 2 years after delivery was 1.7 times higher than that from early pregnancy to 7 days after birth.And nearly 97.88% of birth defects were found within 1 year after birth. Conclusions Prolonging the time period for birth defects surveillance would make data close to the real rate.So it is suggested that the monitoring period of birth defect should be expended to 2 years after birth.