Researchers at University of California Davis and Massachusetts General Hospital have concluded a statistical analysis of nearly 1,000 mother-child pairs in order to study the link between use of antidepressant medications during pregnancy and the possible risk of autism spectrum disorder (ASD) and developmental delays (DD). Their results are published today in the peer-reviewed Pediatrics journal. The 966 mother-child pairs involved were taken from a population study called the CHARGE (for Childhood Autism Risks from Genetics and the Environment) study, at the UC Davis MIND institute.
The current study was led by Professor Irva Hertz-Picciotto at UC Davis Department of Public Health Sciences, who explained that the evidence points to a link between use of antidepressants (known as SSRIs, for Selective Serotonin Reuptake Inhibitors) during pregnancy, and the risk of developing a form of autism. This poses something of a problem for expecting mothers who may be prone to maternal depression, which comes with its own risks. Approximately 10 to 20 percent of women experience depression either during pregnancy or in the first 12 months postpartum. As many as 60 percent of mothers diagnosed with depression are treated with SSRIs. Untreated, maternal depression can manifest itself in poor eating, trouble gaining weight or sleeping, missing prenatal visits or not following the doctor’s instructions, and use of hazardous substances, such as illegal drugs, alcohol, or tobacco. Risks to the fetus include premature birth and low birth weight. Physicians and pregnant women will need to do a thorough assessment of the risks versus benefits of taking the medication.
The researchers looked at children with ASD and DD, as well as those with typical development (TD), aged two to five years, and analyzed the prevalence of prenatal exposure to antidepressants in each category. The children in the three categories were mostly boys – for example 82.5 percent of the children with ASD were boys; 65.6 percent of children with DD were boys; and 85.6 percent of the children with TD were boys. When the numbers were crunched, the researchers found that boys with ASD were three times as likely to have been prenatally exposed to antidepressants as boys with typical development. According to Li-Ching Lee, a psychiatric epidemiologist in the Bloomberg School’s Department of Epidemiology, the greatest risk of ASD was associated with exposure to SSRIs in the first trimester, whereas risk of DD was more strongly associated with exposure during the third trimester. Examination of mothers with an anxiety or mood disorder history produced similar results.
It should be pointed out that the data generated by this study indicates only an association of ASD and DD with prenatal antidepressants exposure, rather than a direct causal link. Although there has been an increase of prevalence of autism, the co-occurring increase in use of SSRIs does not mean that the SSRI use significantly contributes to the prevalence of ASD. Dr. Hertz-Picciiotto used extremely cautious language to describe the risk, stating that:
“…in some children, prenatal exposure to SSRIs may influence their risk for developing an autism spectrum disorder,”
There are a number of difficulties presented by analysis of the data in studies such as these. For example, a low rate of SSRI use in pregnant women means a relatively small sample population. The small sample of children with DD makes analysis of the risk posed by SSRIs somewhat imprecise. Another problem: there is as yet no satisfactory way of telling the effect of the SSRIs on ASD risk apart from the possible effects of the maternal depression that the SSRIs are prescribed for. Also, the study did not take into account the dosage of SSRIs, hence there could be no assessment of dose-response effect. The fact that the children studied were disproportionately boys means that the researchers can only make statements about the link between SSRIs and ASD in boys. Because boys are five times more likely than girls to have ASD, a larger population size will be required to assess the possible impact of prenatal SSRI exposure on risk of ASD in girls. Because of these difficulties, the researchers suggest that the possible contribution of antidepressant use during pregnancy to the increased prevalence of autism is probably minimal.
By Laura Prendergast