OBJECTIVEThis research was to compare the occurrence levels of birth defect, to describe the distribution of primary birth defects in different range of monitored ages and to provide data to China birth-defect monitoring system.

METHODSA retrospective study on birth defect was conducted in two counties, Shanxi province, China, which covered birth defects among fetuses after 20 weeks' gestational age from 2002 through 2004. Data collected on birth defect cases mainly included extrinsic and visceral anomaly.

RESULTSThe occurrence rates of the monitored structural birth defects significantly increased with the increase of age. The occurrence rates were 17.6, 34.0, 43.6, and 53.7 per 1000 births, for different statistical range, from 20-week to 27-week gestational age, 7 days, 1 year and 3 years after birth, respectively. The range from 28-week gestational age to 7 days after birth was usually regarded as the routinely monitored range. If the occurrence rate was calculated from the 20-week gestational age, it appeared a 2.1-time increase. However, if the range was changed to 1 or 3 years after birth, the occurrence rate increased to 2.7 or 3.3 times high, respectively. The distribution of time when birth-defect was identified was significantly different by categories with majority of neural tube defect cases diagnosed at antepartum or 7 days after birth. Visceral defects were mainly found at 7 days after birth but increased with age, even some were diagnosed at 1 year after birth.

CONCLUSIONThe routine Chinese monitoring program might detect approximately 1/3 of those structural birth defects with the base of current technique and monitoring range from 28-week gestational age to 7 days after birth. The result of our findings should be of help to other related studies.