[Epidemiology of birth defects in high-prevalence areas of China]

To study the levels of prevalence and to describe the epidemiological features of birth defects in high-prevalence areas in China.

A population-based retrospective study was conducted in two counties of Shanxi province that including birth defects among fetuses and live births born after 20 weeks' gestational age in the study areas from 2002 through 2004.

During 2002 - 2004, the prevalence of birth defects was 844.2 per 10 000 births in study areas and the first five main birth defects were inguinal hernia (182.2 per 10,000 births), anencephaly (104.4 per 10 000 births), congenital mental retardation (79.4 per 10,000 births), congenital heart diseases (73.2 per 10,000 births) and spina bifida (63.9 per 10,000 births). These five main birth defects accounted for about 60% of total birth defect cases. Inguinal hernia, undescended testicle, congenital mental retardation were usually not included for statistical analysis on birth defect. Excluding these birth defects, the prevalence of birth defects in study areas was 537.2 per 10,000 births and the first five main birth defects were anencephaly, congenital heart diseases, spina bifida, hydrocephaly (40.5 per 10 000 births) and encephalocele (31.2 per 10 000 births). The male prevalence of birth defects was 966.2 per 10 000 births, which was significantly higher than prevalence in females. The prevalence rates of birth defects for maternal age groups under 20 years old and over 30 years old were remarkably higher than those for 20-24 year and 25-29 year old mothers. The teenage mothers were at higher risk of having a child with neural tube defects(NTDs) or congenital heart diseases. Prevalence rates under 20 year maternal age group were 408.8 and 188.7 per 10 000 births for NTDs and congenital heart diseases respectively, whereas corresponding rates were 204.8 and 91.0 per 10 000 births for groups over 30 years of age. The prevalence rates increased with increasing gravidity or parity.

This study showed that the patterns of birth defects in study areas were very different from those of other areas, with an unusually high prevalence of NTDs. The study also suggested that both young and advanced mothers were at increased risk of having a child with a birth defect.