In 1991 the Medical Research Council Vitamin Study Group and in 1992 the Hungarian randomised clinical trial have shown conclusively that the risk of neural tube defects can be reduced substantially by taking folic acid during the peri-conceptional period. At present there is enough evidence to support the hypothesis that folic acid supplementation can reduce the risk of all congenital malformations or of a specific and selected group of them, namely: neural tube defects, oral clefts, cardiac defects, urinary tract anomalies except hypospadias, limb reduction defects, omphalocele, anal atresia and trisomy 21.

The hypothesis that a higher intake of folic acid is related to an higher risk reduction of neural tube defects and of other congenital malformations is the main rationale for the present study.

The present study is a randomized, double-blind, controlled trial evaluating whether supplementation with folic acid at high dose (4 mg/day) reduces the overall risk of major congenital malformations in the population more than the standard recommended dose (0.4 mg/day). At the enrolment visit all the eligible women will be interviewed to assess sociodemographic, life style and health status. After randomization, women will be interviewed every 4 months to evaluate pregnancy status. Women who have a pregnancy diagnosis during the study period will be interviewed by telephone at the expected 16, 24 and 40 weeks of gestation to evaluate the pregnancy outcome. The health status of live births will be evaluated at the child's age of 1 month, 3 months and 1 year.

The primary aim of this project is conducting a study to assess the effect of folic acid periconceptional supplementation of 4 mg/day compared to the 0.4 mg/day standard dose on reducing the occurrence of all congenital malformations. Secondary aims of this study include comparing severity of CMs in offspring of trial mothers, rates of "selected congenital malformations", rates of twinning, miscarriages, recurrent abortions, small-for-gestational age, preeclampsia and abruptio placentae. The sample size is not easy to be computed because lacking robust estimate of the size effect of the treatment. Three hypotheses of a size effect of 45%, 26% and 13% were considered. A sample size of outcomes (and women) respectively of 2,006 (5,015), 8,510 (21,275) and 30,126 (75,315) is needed. Since the sample size needed to evaluate different scenarios is large, the present study is also the pilot study to promote an international prospective meta-analysis.

Inclusion Criteria:

• age between 18 and 44 years
• women who intend to become pregnant (not excluded women

Exclusion Criteria:

• pregnant women
• women planning to move to an area where the study is not ongoing
• women who do not understand and speak Italian
• women who do not have a phone
• women affected by epilepsy, even not assuming anticonvulsivant drugs
• women affected by diabetes
• women who previously had a tumour or a disease relevant for the study (Crohn disease, rheumatoid arthritis, ulcerative colitis)
• women who recently assumed antifolates, like methotrexate
• women who currently abuse or previously abused alcohol
• obese women
• vegetarian women
• women who had a previous pregnancy with neural tube defect (NTD) or any other congenital structural defect
• women or partners with NTD, or one of their relatives with an NTD
• women with positive family history for breast or colorectal cancer
• women with positive family or personal history of hereditary syndrome like adenomatous polyposis, or hereditary nonpolyposis colorectal cancer
• women allergic to folic acid
• women presenting contraindications to folic acid
• women affected by megaloblastic anaemia
• assuming folic acid at defined doses for conditions other than those already mentioned