Effect of oral contraceptives on blood folate levels in pregnancy.
An investigation was carried out to assess residual effects of oral contraceptives on the folate status of pregnant women who had discontinued intake of these drugs within six months of conception. The sample population of middle class women consisted of users and nonusers of oral contraceptives of similar age groups. Subgroups were those studied initially during the summer (May to July) or winter (October to January). Red blood cell folate values showed seasonal variability and were lower in the winter months. Oral contraceptive users had lower plasma and red blood cell folate values than did the respective control subjects. Red blood cell folate values were more affected by previous drug use in the winter group than in the summer group. Dietary folate was found to have a significant effect on plasma and red cell folate; such for any one level of intake, blood folate values were significantly lower in oral contraceptive users.