The peer-reviewed medical journal Human Reproduction has published a study performed by the Centers for Disease Control and Prevention on the possible risk of birth defects from clomiphene.

Clomiphene is one of the trade names of a drug also called clomifene, sold as Androxal, Clomid, and Omifin. The drug is used to treat certain types of infertility in women. Specifically, clomiphene is used to treat types of infertility wherein a women’s body does not release egg cells, or does so irregularly. This is a major cause of infertility, but with drugs like clomiphene it is a treatable condition. Women who suffer from this type of infertility typically have a clinical pregnancy rate of 1.3 to 4.2 percent without treatment, and a rate of 5.6 percent with clomiphene. This means that for some women, clomiphene can increase their odds of fertilization more than four-fold. But CDC research has found a possible risk of clomiphene birth defects.

CDC Clomiphene Birth Defects Study

In the CDC clomiphene birth defect study, the agency used data from the National Birth Defects Prevention Study, which collected data from more than 40,000 women who had given birth to a child between 1997 and 2011. The research was a case-control study, a type of study where people are found with an outcome (in this case, birth defects), then questioned about possible factors that could contribute to it.

The National Birth Defects Prevention Study Collected data from over 30,000 women who had children with birth defects, and 10,000 who did not for comparisons. The National Birth Defect Prevention Study contains a vast wealth of data, and even though it stopped collecting information in 2011, new studies continue to mine the results for new data, such as this latest CDC clomiphene study.

The key findings of the CDC clomiphene birth defect study are available on the CDC’s website. CDC researchers found that women taking clomiphene were more likely to have children with six different birth defects. The study also found that clomiphene was less strongly linked to three other birth defects. The latter birth defects were less common, making it harder for statisticians to establish the strength of the clomiphene birth defects link.

For some of the possible clomiphene birth defects, this was the first time these types of conditions had been linked to clomiphene at all. The new birth defects found in the CDC’s clomiphene birth defect study included heart and skull defects, as well as a condition wherein a baby is born with major organs outside the body. Many of the birth defects described in the CDC clomiphene birth defect study are life-threatening and may require surgical correction.

The one drawback to this type of birth defects study is that researchers can say that women who take clomiphene are more likely than their peers to have children with birth defects, but it is harder to prove that clomiphene is the cause of the birth defect. Researchers must acknowledge the risk of cofounders—that is, possible hidden risk factors.

For example, it is possible that women who have problems ovulating are more prone to birth defects than the general population, and this makes them more likely to take clomiphene. In this case, infertility would be the cofounder which creates the appearance that clomiphene increases the risk of these birth defects. However, the legal system has a different way of weighing the risks of birth defect risks than the medical community, and if nothing else, this research indicated the need for further research into the clomiphene birth defects.