Taking medications that reduce or block the actions of folic acid during the first trimester of pregnancy increase the risk that the growing baby will develop abnormalities.
The study was conducted by researchers at Ben-Gurion University of the Negev.
For the study, the researchers obtained medication data from pregnant mothers registered at Clalit HMO, Southern District, and drew information from 84,832 babies born at Soroka University Medical Center in Beer-Sheva, Israel.
"After studying the data, we concluded that first trimester exposure to folic acid antagonists is associated with increased risk for neural tube, cardiovascular and urinary tract defects," said principal investigator Dr. Rafael Gorodischer, professor emeritus at Ben-Gurion University of the Negev.
Healthcare professionals now encourage women to take folic acid supplements or eat food fortified with folic acid if they are planning to get pregnant, as well as during early pregnancy because there is clear evidence that this reduces the risk of any resulting baby having neural tube defects and possibly other birth defects (congenital malformations).
The researchers considered the effects of two groups of medications on pregnancy. Each group consists of drugs that prevent folic acid working in the body.
One group (dihydrofolate reductase inhibitors) prevents folate from being converted into its active metabolites and includes trimethoprim (antibiotic), sulfasalazine (for ulcerative colitis) and methotrexate (chemotherapeutic).
The other medications are known to lower serum and tissue concentrations of folate by various mechanisms, and include antiepileptics (carbamazepine, phenytoin, lamotrigine, primidone, valproic acid and phenobarbital) and cholestyramine (reduces cholesterol).
Dr. Amalia Levy, an epidemiologist with the BGU Faculty of Health Sciences and chair of the BeMORE collaboration, said: "The study shows that exposure to folic acid antagonist in the first trimester of pregnancy more than doubles the risk of congenital malformations in the fetus, and that neural tube defects, such as spina bifida and malformations of the brain, increase by more than six-fold after exposure to these antagonists."
The study just published in the British Journal of Clinical Pharmacology.