ABSTRACT
Objective To examine the impact of pregnancy termination before 28 weeks of gestation on the overall prevalence of neural tube defects (NTDs).Methods Data collected during the period of 2004 and 2010 from a birth defects surveillance system in Pingding county and Talgu county of Shanxi province were used.Number of births ≥28 weeks of gestation and number of cases with major birth defects among the births were collected.Terminations of pregnancies before 28 weeks of gestation due to prenatal diagnosis were also collected.The total prevalence of neural tube defects,prevalence before 28 weeks of gestation,and prevalenee of ≥28 weeks gestation were calculated using the total number of pregnancies of ≥28 weeks of gestation as denominator.The prevalence data were compared to examine the impact of pregnancy termination on the total prevalence.The proportions of pregnancy terminations before 28 weeks of gestation due to prenatal diagnosis of an NTD against the total number of NTD cases were also calculated.Results During 2004-2010,52 366 births were recorded,and 485 NTD cases were ascertained.The overall prevalence of NTDs was 92.6 per 10 000 births,with prevalence of ＜28 weeks gestation due to pregnancy terminations as 60.9 per 10 000 births,while the prevalence of ≥28 weeks of gestation was 31.7 per 10 000 births.NTD prevalence of ≥28 weeks gestation was 66.0％ lower than the total NTD prevalence.In the last two years,the proportion of NTDs ascertained ≥28 weeks gestation accounted for about 40.0％ of the total NTD cases.Conclusion A birth-defect-surveillance program that covered only tregnancies ≥28 weeks of gestation resulted in a severe underestimation of the total birth prevalence of NTDs,especially for anencephaly.We would recommend that the current national birth defects surveillance system should include pregnancy terminations before 28 weeks of gestation and the calculation of total NTD prevalence should also include these cases into the numerator,so as to better estimate true population NTD prevalence,upon which the related public health policy is based.