Regional variations in neural tube defects and alfa-fetoprotein screening in Denmark 1983-88.

Abstract

An effect of maternal serum alpha-fetoprotein screening on prevalence rates for neural tube defects (NTD's) has been demonstrated in some populations. The present study tests the hypothesis that regional rates in the Danish low risk population reflects screening activities. Cross-sectional survey for neural tube defects through the Danish Malformation Register. The prevalence rate for all neural tube defects was 5.8 pr 10(4) births which is lower than in most other populations. Standardized risk ratios for NTD in two regions with a program for alfa-fetoprotein screening were 0.1 (95% c.i. 0.0-0.7) and 0.4 (95% c.i. 0.2-0.9). Relative risk at 0.6 (95% c.i: 0.4-1.1) was found in one county with screening of approximately one third of pregnancies. In most other counties < 5% of pregnant women had been examined and point estimates of relative risks varied from 0.9-1.7. There was a good agreement between prevalence of neural tube defects at birth and regional alfa-fetoprotein screening activity. This can be taken as a strong indication of a secondary preventive effect from screening in a population with a priori low risk for NTD's. However, other aspects of screening should also be taken into consideration before general programs are forwarded.