Periconceptional exposure to contraceptive pills and risk for Down syndrome

There are some studies which analyzed the relationship between prenatal exposure to oral contraceptives (OCs) and Down syndrome, with conflicting results even in women using OCs and conceiving at different intervals after discontinuing the use of contraceptive pills. We analyzed the risk for Down syndrome in infants of women who become pregnant while taking OC.

We used the data from the Spanish Collaborative Study of Congenital Malformations (ECEMC). The ECEMC is a case-control study and surveillance system. For each malformed infant (case), the next non-malformed infant of the same sex born in the same hospital is selected as a control subject, from whom the collaborating physicians collected the same data as for the malformed infant. For the present study, we used two different approaches. First, the pair-matching analysis. Second, a case-control using the rest of the total of 17,183 controls from the ECEMC database with specified data on maternal use of OCs and maternal age. To control for maternal age, we used a logistic regression analysis.

The results show an increased risk of 2.8-fold for infants with Down syndrome in women younger than 35 years of age if the mother became pregnant while she was taking OCs. We did not observe this result for women older than 34 years of age.

Our results showed that the risk for Down syndrome in infants born to mothers with less than 35 years of age (as a group) who became pregnant while taking OCs is near the risk for Down syndrome of mothers with more than 34 years of age, women who are candidates for prenatal diagnosis. Thus, based on our results, one may consider the possibility of offering prenatal diagnosis for Down syndrome to young women who became pregnant while taking OCs.