Neural tube defects in the Czech Republic during 1961-1999: incidences, prenatal diagnosis and prevalences according to maternal age.

We set out to present the incidences of the neural tube defects (anencephaly, spina bifida and encephalocele) and to document maternal age distribution and the influence of the prenatal diagnostics on incidences in neonates. We also analysed maternal age as a risk factor for the defects studied. This was a retrospective epidemiological study of neural tube defects using data from the population-based register of congenital malformations in the Czech Republic over the 1961-99 period. The total number of neural tube defects detected both pre- and postnatally was 4696 in this period (anencephaly 1857, spina bifida 2420 and encephalocele 419 cases). In this period, a significant decrease (due to improved prenatal diagnostic efficiency) in the above-mentioned defects occurred in the Czech Republic. No statistically significant correlation between any of the particular defects and the maternal age was revealed. However, neural tube defects as a whole show some correlation, the probability of these defects occurring being higher than expected in 15- and 32-year-old mothers. By application of the two-sided 95% CI, statistically significant correlation was found in 15-, 35- and 39-year cohorts; in other age-groups above the age of 32 years this correlation was neither confirmed nor rejected. In this study, maternal age as a risk factor for the origin of neural tube defects has not been statistically confirmed. However, probability estimate makes this correlation possible. Statistical methods in use reveal the risk for these defects (regarding their relative incidences) only in maternal age groups of 15, 35 and 39 years.