"We found that over the course of a year, one in six women of reproductive age filled a prescription for a medication labeled by the Food and Drug Administration as increasing the risk of fetal abnormalities," said Eleanor Bimla Schwarz, M.D., assistant professor in the departments of medicine and obstetrics, gynecology and reproductive medicine at the University of Pittsburgh School of Medicine and first study author. "Unfortunately, many women filling prescriptions that can increase risk of birth defects remain at risk of pregnancy."
Half of pregnancies in the United States are unintended, according to national estimates. While regular use of contraception can prevent unplanned pregnancies, women filling prescriptions that can increase the risk of birth defects are no more likely to use contraception than other women, the study authors note.
For this investigation, Dr. Schwarz and colleagues studied patient data related to all prescriptions filled by 488,175 reproductive-aged women enrolled with a large managed health care plan during 2001. Prescriptions involved drugs considered safe for use in pregnancy and those labeled as posing a fetal risk.
The researchers examined use of contraception and results of pregnancy tests. When they compared medications labeled as increasing the risk of birth defects to safer medications, the researchers found little difference in rates of contraceptive counseling, use of contraception or subsequent pregnancy test results.
"Many women - and perhaps their physicians - may be unaware of the risks associated with the use of some medications, the chance that women may become pregnant, or both," said Dr. Schwarz, who also is an assistant investigator at the Pitt-affiliated Magee-Womens Research Institute. "The scary thing is that we know women in other primary care health care settings are even less likely to get information about birth control."
While about half of the women in this study had received contraceptive counseling, other studies have shown that nationwide, only about 20 percent of women are advised to use birth control when they receive potentially dangerous medications.
"While efforts are needed to ensure that women get information about birth control and the risk of medication-induced birth defects, it also is important to realize that different birth control methods are not equally effective," she said. "Women who were using the most effective methods of contraception, such as the intrauterine device or IUD, were least likely to have a positive pregnancy test after filling a prescription for a potentially dangerous medication."
The researchers found that internists and family practitioners prescribed the largest proportion (48 percent) of riskier medications to women of childbearing age. Psychiatrists prescribed 15 percent of these drugs; dermatologists, 12 percent; obstetrician/gynecologists, 6 percent; and pediatricians, 3 percent, according to the study.
"Women should not avoid using prescription medications, but clinicians need to remember that sometimes birth control is needed until a woman is ready to have a healthy pregnancy and a healthy baby," Dr. Schwarz added.
This study was funded by the National Institute of Child Health and Human Development and an unrestricted grant from Duramed Pharmaceuticals.
In addition to Dr. Schwarz, other authors are Debbie A. Postlethwaite, R.N.P.; Yun-Yi Hung, Ph.D.; and Mary Anne Armstrong, M.A., of Kaiser Permanente Northern California.