March 22, 2011

Study Finds Using Oral Contraceptives Before Pregnancy, Not Linked to Respiratory Problems

Media Contacts

Dana B. Hancock
Dana B. Hancock

RESEARCH TRIANGLE PARK, N.C.—A new study by researchers at RTI International, the National Institute of Environmental Health Sciences, and the Norwegian Institute of Public Health refutes previous findings that oral contraceptive use before pregnancy is linked to respiratory problems in children.

The Norwegian study, presented at the 2011 Annual Meeting of the American Academy of Allergy, Asthma & Immunology and published in Pediatric Allergy and Immunology, may reassure mothers who have used oral contraceptives before becoming pregnant.

"Given that progesterone is a key hormone in pregnancy, researchers have hypothesized that the use of progestin-containing oral contraceptive pills before pregnancy could influence fetal respiratory and immune development," said Dana B. Hancock, Ph.D.., genetic epidemiologist at RTI and the study's lead author. "In 1997, researchers first reported that a mother's oral contraceptive pills use may increase the risk of asthma in the child. Since then, a few studies have supported this hypothesis but data are limited and inconclusive."

According to the researchers oral contraceptive pills are widely used. Intended pregnancies often occur shortly after discontinuing oral contraceptive pills, and almost half of unintended pregnancies occur when women are using contraceptives. Effects of oral contraceptive pills on hormone levels can linger in women months to years after discontinuation.

In this new study, the results showed that the use of estrogen-progestin combined pills before pregnancy was not associated with lower respiratory tract infections, wheezing or asthma in the children followed in the study.

The researchers looked at associations between the type of oral contraceptive used by the mother before pregnancy and lower respiratory tract infections in more than 60,000 children followed to 6 months old; lower respiratory tract infections and wheezing in more than 42,500 children followed to 18 months old; and asthma in almost 24,500 children followed to 36 months old.

Progestin-only pill use in the year before pregnancy had a slight positive association with wheezing in children at 6 to 8 months old but the researchers noted that very few women used this type of pill, the association was small and might be due to residual confounding.

"We found that use of the combined pill, taken by most women who use oral contraceptive pills, was not associated with adverse respiratory outcomes in the offspring" said Stephanie J. London, M.D., Dr.P.H., principal investigator at the National Institute of Environmental Health Sciences and senior author of the study. "This should provide reassurance to the vast majority of women using oral contraceptive pills during their childbearing years."