On 2016 Apr 16, Aiguo Ren commented:

The lowest and highest point estimates of NTD prevalence were obtained from two studies in China. However, these two studies are not comparable in terms of geographical area, time period, and, most importantly, method of calculation. The estimate from Beijing was obtained from a maternity hospital and the numerator was the number of NTD cases in pregnancies of 28 weeks of gestation or greater. In Beijing, every pregnant woman receives ultrasound scanning for fetal structural defects around 20 weeks of gestation, and virtually all fetuses with NTDs will be detected by 28 gestational weeks, and terminated based on informed choice of the mother. This explains, in a larger part, the low NTD prevalence in Beijing. Other national or hospital-bases data from China suffer from the same problem. Please see our most recent report PMID: 26879384.

On 2016 Apr 16, Aiguo Ren commented:

The lowest and highest point estimates of NTD prevalence were obtained from two studies in China. However, these two studies are not comparable in terms of geographical area, time period, and, most importantly, method of calculation. The estimate from Beijing was obtained from a maternity hospital and the numerator was the number of NTD cases in pregnancies of 28 weeks of gestation or greater. In Beijing, every pregnant woman receives ultrasound scanning for fetal structural defects around 20 weeks of gestation, and virtually all fetuses with NTDs will be detected by 28 gestational weeks, and terminated based on informed choice of the mother. This explains, in a larger part, the low NTD prevalence in Beijing. Other national or hospital-bases data from China suffer from the same problem. Please see our most recent report PMID: 26879384.