In recent years, numerous studies have reported that there may be a link between maternal use of a class of antidepressants known as selective serotonin reuptake inhibitors and greater risk of birth defects. Now, a new study provides further evidence of this association.

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Researchers linked use of the SSRIs paroxetine and fluoxetine in early pregnancy with greater risk of birth defects, but no such association was found with maternal use of other SSRIs.

The study reveals that women who used certain selective serotonin reuptake inhibitors (SSRIs) in early pregnancy were more likely to have offspring with heart problems and abnormal brain and skull formation, among other birth defects.

Study co-author Jennita Reefhuis, of the National Center on Birth Defects and Developmental Disabilities at the Centers for Disease Control and Prevention (CDC), and colleagues publish their findings in The BMJ.

The team notes, however, that if the link between SSRI use in pregnancy and birth defects proves causal, the increase in absolute risks for such conditions are low, though they call for further research on the issue.

According to the US Department of Health and Human Services, around 13% of pregnant women and new mothers experience depression. While some of these women find talking therapy alone to be an effective treatment, others may require antidepressant medication, with SSRIs being one of the most common forms.

However, while some studies claim maternal SSRI use is safe, others have associated it with greater risk of birth defects, raising concerns among clinicians and mothers-to-be.

“SSRIs are increasingly used by women of reproductive age and during pregnancy, but the inconsistent reports have limited opportunities for clinicians to carefully evaluate the risk compared with benefit of specific SSRIs for a given patient during pregnancy,” say Reefhuis and colleagues.

To get a better estimate of the link between maternal SSRI use and birth defects, the team analyzed data from the US National Birth Defects Prevention Study (NBDPS), including 17,952 mothers of infants with birth defects and 9,857 mothers of infants without birth defects. Infants were born between 1997 and 2009.

SSRI use among the mothers was assessed via medical questionnaire. The team recorded use of the following SSRIs among the women from 1 month before conception up until the third month of pregnancy: citalopram (Celexa), escitalopram (Lexapro), fluoxetine (Prozac), paroxetine (Paxil) or sertraline (Zoloft).

The researchers excluded any mothers with pre-existing diabetes and mothers who were taking non-SSRI antidepressants.

The results of the analysis revealed that maternal use of the SSRI paroxetine was associated with five birth defects, including heart defects, such as right ventricular outflow tract obstruction, and anencephaly – abnormal brain and skull formation. Fluoxetine use in early pregnancy was linked to greater risk of heart wall defects and craniosynostosis – abnormal skull shape.

The most commonly used SSRI was sertraline – with 40% of mothers using this drug in early pregnancy. But despite previous research suggesting an association between maternal use of sertraline and increased risk of birth defects, the researchers found no such link, which they say is “reassuring” given its widespread use among expectant mothers with depression.

While this study provides some reassurance about the use of certain SSRIs during pregnancy, it raises concerns about the use of paroxetine and fluoxetine. However, Reefhuis and colleagues say that if the link between maternal use of these SSRIs and greater risk of birth defects is causal, the increase in absolute risks is small.

“If these associations are causal, the absolute risks in the children of women who are treated with paroxetine early in pregnancy would increase for anencephaly from 2 per 10, 000 to 7 per 10,000, and for right ventricular outflow tract obstruction cardiac defects from 10 per 10,000 to 24 per 10,000,” they note.

Still, the team says further studies into the link between maternal SSRI use and risk of birth defects are required. They add:

Continued scrutiny of the association between SSRIs and birth defects is warranted, and additional studies of specific SSRI treatments during pregnancy and birth defects are needed to enable women and their health care providers to make more informed decisions about treatment

Meanwhile, the current analysis can help guide health care providers and women to the safest options for treatment during early pregnancy to minimize the risk of major birth defects, while providing adequate treatment of maternal depression.”

Last month, Medical News Today reported on a study linking maternal SSRI use in late pregnancy with greater risk of persistent pulmonary hypertension of the newborn – a condition in which a baby’s blood circulation does not allow them to breathe properly outside the womb.