Prevalence of neural tube defect pregnancies in China and the impact of gestational age of the births from 2006 to 2008: a hospital-based study

Objective: To determine the prevalence of pregnancies with neural tube defects (NTDs) in China between 2006 and 2008 and to find a better representative monitoring gestational age for total prevalence of NTDs by comparing the prevalence at or greater than 20, 22 or 28 weeks of gestation (abbreviated as P20, P22 and P28, respectively). Methods: The data were retrieved from the National Birth Defects Monitoring Network in China (the Network). All births were monitored on the prevalence of NTDs during the entire gestation period of 2006-2008. Results: The P28 only represents 34.6% of anencephaly, 70.8% of spina bifida, 53.3% of encephalocele and 53% of the combination of the three types of NTDs during the entire pregnancy. The P20 represents 75.8%, 94.7%, 86% and 85.4% in the above-mentioned categories, respectively. Of the NTDs diagnosed prenatally before 28 weeks of gestation, 45.3% were terminated electively. Conclusions: The P28 underrepresented 65.4% of anencephaly, 29.2% of spina bifida, 46.7% of encephalocele and 47% of the combined NTDs. The prevalence of NTDs that occurred at or greater than 20 weeks of gestation was more accurate than that at or greater than 28 weeks of gestation.