The influence of folic acid supplement on the outcome of pregnancies in the county of Funen in Denmark. Part II. Congenital anomalies. A randomised study

Abstract

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. Folic acid dose was randomised to 2.5 or 1.0 mg. A randomised control group was not feasible for ethical reasons. Hospitals, midwives and most general practitioners cooperated to procure information on close to all pregnancies and congenital anomalies were recorded.

Results and conclusions: In a total of 14,021 pregnancies resulting in child birth 8184 women (58.4%) had folic acid with randomisation. Supplement was started in the randomised group before the last menstrual period in 1359/8184 (16.6%) and in the first 19 weeks of pregnancy in 6825/8184 (83.4%). The prevalence of congenital anomalies was 224 in 8293 children (27.0/1000). No dose-dependent differences were found in either total anomalies or in those specific malformations which have been reported to occur with reduced prevalence with periconceptional folic acid. The result was probably influenced by a start of supplement too late to affect malformation development in many cases and by the high level of both folic acid doses given compared to usual recommendations. Pregnancies without folic acid supplement showed prevalences similar to the supplemented groups.