OBJECTIVETo describe and analyze epidemiological characteristics of babies with neural tube defects (NTD) by sex and birth outcome in a high-prevalence and a low-prevalence areas of China.

METHODSBirth defects surveillance data collected from 1992 through 1994, as a part of the Sino-American cooperative project on NTD prevention, were used to classify NTD as four categories, i.e., anencephaly, encephalocele, high-level and low-level spina bifida according to the sites of lesion (high vs. low level lesion were cervicothoracic and lumbosacral, respectively). Each category was sub-classified, according to single or compound defect, as isolated external defects (including those with NTD only) or multiple external defects (including those with NTD and another major external birth defects that is not the sequence of a defect such as cleft lip with or without cleft palate). The rates of anencephalus, encephalocele, high- and low-level spina bifida (SB) in males and females and their sex ratios were calculated, adjusted for urban and rural areas, season, category and birth outcome by sex and sites of lesions (high vs. low).

RESULTSTotally, 784 NTD cases were identified from 326 874 recorded births (including live births, stillbirths and fetal deaths with a gestation age of at least 20 weeks). The prevalence rates of anencephalus (1.30 per 1 000 female births) and high-level SB (3.99) in females were higher than those (0.66 and 1.66 per 1 000 male births) in males in the high-prevalence northern regions; with adjusted prevalence rates of females 1.8 - 2.1 times greater than those of males. In the low-prevalence southern regions, the prevalence of high- (0.32 per 1 000 female births) and low-level SB (0.21) in female were higher than those in males, with high- and low-level SB rate of 0.10 and 0.09 per 1 000 male births), with adjusted rates for females of 1.3 - 1.6 times higher than in males. Isolated NTD accounted for more than 80% of all NTD cases, and the prevalence of isolated NTD in females (2.57) was higher than that in males (1.40).

CONCLUSIONSThe sex differences in NTD existed between north and south, in accordance with the phenotype of NTD. It suggested that proportion of high level SB and anencephalus in females could increase as the prevalence of NTD going up, anencephaly, high- and low-level SB had the different genetic and environmental background.