REGIONAL VARIATIONS IN NEURAL-TUBE DEFECTS AND ALFA-FETOPROTEIN SCREENING IN DENMARK 1983-88

Background. An effect of maternal serum alpha-fetoprotein screening on prevalence rates for neural tube defects (NTD's) has been demonstrate d in some populations. The present study tests the hypothesis that reg ional rates in the Danish low risk population reflects screening activ ities. Methods. Cross-sectional survey for neural tube defects through the Danish Malformation Register. Results. The prevalence rate for al l neural tube defects Tvas 5.8 pr 10(4) births which is lower than in most other populations. Standardized risk ratios for NTD in two region s 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. C onclusion. There was a good agreement between prevalence of neural tub e defects at birth and regional alfa-fetoprotein screening activity. T his can be taken as a strong indication of a secondary preventive effe ct from screening in a population with a priori low risk for NTD's. Ho wever, other aspects of screening should also be taken into considerat ion before general programs are forwarded.