The influence of folic acid supplement on the outcome of pregnancies in the county of Funen in Denmark. Part III. Congenital anomalies. An observational study.

Objective: The effect of folic acid supplement on the prevalence of congenital anomalies was studied in a Danish population.

Material And Methods: From 1983 to 1986 all Danish women resident in the county of Funen were offered free folic acid when pregnant or planning a pregnancy. Data concerning the starting time of folic acid supplement and congenital anomalies were recorded on close to all pregnancies. Children of folic acid supplemented mothers were subdivided as to start of supplement with dividing lines at week 7 and week 11 calculated from the last menstrual period. Structural malformations were subdivided into an early group with malformation development in the first 7 weeks from the last menstrual period and a late group where malformations develop in weeks 8 to 11.

Results: In a total of 14,021 pregnancies 10,494 pregnant women (74.8%) had folic acid supplement. No folic acid was taken by 2721 women (19.4%) and in 806 cases (5.8%) information was lacking. The prevalence of congenital anomalies was 380 in 14,185 children (26.7/1000). Children whose mothers started folic acid supplement before the 7th week of pregnancy showed a significantly lower prevalence of the malformations which develop in the first 7 weeks, when compared to pregnancies with a later start of supplement. The result was interpreted as a clearcut trend.