The Centers for Disease Control and Prevention backed a study that found that the active ingredient in Clomid, a common infertility drug, is linked to an increased risk of several serious birth defects.

The CDC-backed study was peer-reviewed and published in the medical journal Human Reproduction. Researchers drew from data collected by the National Birth Defect Prevention Study (NBDPS), which was a data-mining operation that collected data from mothers of more than 30,000 children with various birth defects between 1997 and 2013.

For a control group, data was also collected from 10,000 women who had children with no birth defects. Though this study stopped collecting data in 2013 (and the births in question took place no later than 2011), enough data was collected for years worth of research into the causes of birth defects.

In this particular study, researchers performed statistical analysis on the birth defect prevention data and used it to see if mothers taking Clomid had a higher risk of birth defects than their peers. The Human Reproduction study suggests just that.

According to the National Birth Defects Prevention Study, women taking Clomid were more likely to have babies who developed birth defects than their peers. Clomid is a drug used to treat several forms of infertility, including conditions in which otherwise healthy women do not release or erratically release egg cells from their ovaries.

About a half-dozen birth defects were closely linked to Clomid, including heart defects, skull defects, and other birth defects. A smaller number of other types of birth defects were also observed — though still at a higher rate than women taking Clomid.

These less-common possible Clomid birth defects included cloacal estrophy, a rare birth defect wherein the abdomen is severely malformed, with the bladder and intestines on the outside of the body, the genitals misformed and the anus sometimes sealed.

However, there is some call for hesitation in blaming these sometimes-horrific birth defects on Clomid. The CDC study was an observational study. This means that the researchers did not have strict control over the test subjects, and drew their conclusions by collecting data from people outside of their control.

Unlike more direct experiments like clinical trials, researchers doing this kind of research cannot fully rule out the possibility of outside factors confusing their data. In this case, it could be possible that women who have the types of infertility treated by Clomid are already predisposed to having children with severe birth defects.

However, other Clomid birth defect studies have found similar results, adding strength to the idea that Clomid could be linked to birth defects.

Additionally, the legal system has a different way of looking at evidence of cause and effect than the scientific community. In some cases, this could mean that the court system has a lower standard of evidence than the scientific community. This could pave the way for Clomid birth defect lawsuits, filed by mothers who have allegedly had children with Clomid birth defects after taking the fertility treatment drug.