Folic acid may not only reduce the incidence of neural tube defects but also reduce congenital cardiovascular anomalies

A dose of 4mg/day folic acid alone could reduce neural tube defects (NTD) occurrence by 71% and also prevented cleft lip occurrence. While folic acid by itself can reduce the incidence of NTD, the use of multivitamins containing folic acid and other B group vitamins are more efficacious.
A multivitamin supplement (0.4µg B12, 2.6mg B6, 1.8mg B2 and 0.8mg folic acid), was shown to successfully prevent NTD (no reported cases) and a significant reduction in total congenital abnormalities was also found. Among these congenital abnormalities were ventricular septal defects which were reduced by about 74%. Cardiovascular congenital abnormalities (CCA) are one of the most common major congenital abnormalities and represent almost half of congenital abnormality-related infant death. Around 7-8 births in every 1000 live births are affected by CCA. In Quebec, folic acid fortification of grains resulted in a statistically significant 6% reduction in severe CCA.

When proteins from meat, fish or plants are digested into amino acids, methionine (an amino acid) is converted to the toxic homocysteine which is usually neutralized immediately. It requires vitamin B6 to be metabolized. Re-methylation of homocysteine back to methione requires vitamin B12 and folate (5-methyl-tetrahydrofolate) as a methyl donor. Thus being deficient in folate as well as B6 and B12 can cause homocysteine levels to rise and increase the risk of congenital abnormalities such as NTD and CCA.
Folate can only be obtained through the diet or supplements as it is not made in the body. A 5mg daily dose of folic acid was suggested to be useful in potential pregnancies, which is far above the tolerable upper limit of 1mg of folic acid. The study that found folic acid to be effective in reducing 90% of NTD in a Hungarian population used 0.8mg folic acid. This review also highlights the importance of other B vitamins for the prevention of congenital abnormalities such as NTD.

Folic acid can be found in PM Procare (Pregnancy & Breastfeeding formula and AB Extra bone-care + (comprehensive calcium supplement).

Reference
Czeizel, A.E. and F. Banhidy, Vitamin supply in pregnancy for prevention of congenital birth defects. Curr Opin Clin Nutr Metab Care, 2011. 14(3): p. 291-6.