Using antidepressants during pregnancy, specifically selective serotonin reuptake inhibitors (SSRIs), greatly increases the risk of autism, a new study shows.

The new research, published online today in JAMA Pediatrics, is among the strongest findings that link antidepressant use in pregnancy to poor outcomes. It found that women who took antidepressants in the last six months of pregnancy were 87% more likely to have a child later diagnosed with autism.

Professor Anick Bérard of the University of Montreal and its affiliated CHU Sainte-Justine children’s hospital worked with data from a Canadian registry of newborn children who were followed for an average of about six years. The medical records of the babies’ mothers were available for at least a year before their birth, allowing researchers to look at whether and when the babies’ pregnant mothers took SSRIs (antidepressants marketed as Prozac, Zoloft, and Lexapro).

Prof. Bérard, who is an expert in the fields of pharmaceutical safety during pregnancy, came to her conclusions after reviewing the data. She said of the findings:

The variety of causes of autism remain unclear, but studies have shown that both genetics and environment can play a role. Our study has established that taking antidepressants during the second or third trimester of pregnancy almost doubles the risk that the child will be diagnosed with autism by age 7, especially if the mother takes selective serotonin reuptake inhibitors, often known by its acronym SSRIs.

From the press release:

Bérard and her colleagues worked with data from the Quebec Pregnancy Cohort and studied 145,456 children between the time of their conception up to age ten. In addition to information about the mother’s use of antidepressants and the child’s eventual diagnosis of autism, the data included a wealth of details that enabled the team to tease out the specific impact of the antidepressant drugs. For example, some people are genetically predisposed to autism (i.e., a family history of it.) Maternal age, and depression are known to be associated with the development of autism, as are certain socio-economic factors such as being exposed to poverty, and the team was able to take all of these into consideration.

Prof. Bérard said:

We defined exposure to antidepressants as the mother having had one or more prescription for antidepressants filled during the second or third trimester of the pregnancy. This period was chosen as the infant’s critical brain development occurs during this time. Amongst all the children in the study, we then identified which children had been diagnosed with a form of autism by looking at hospital records indicating diagnosed childhood autism, atypical autism, Asperger’s syndrome, or a pervasive developmental disorder. Finally, we looked for a statistical association between the two groups, and found a very significant one: an 87% increased risk.

The results remained unchanged when only considering children who had been diagnosed by specialists such as psychiatrists and neurologists.

The findings are very important, because six to ten percent of pregnant women are currently being treated for depression with antidepressants. In the current study, 1,054 children were diagnosed with autism (0.72% of the children in the study), on average at 4.5 years of age.

In addition, the prevalence of autism among children has increased from 4 in 10,000 children in 1966 to 100 in 10,000 today. While that increase can be attributed to both better detection and widening criteria for diagnosis, researchers believe that environmental factors are also playing a part.

Prof. Bérard elaborates:

It is biologically plausible that anti-depressants are causing autism if used at the time of brain development in the womb, as serotonin is involved in numerous pre- and postnatal developmental processes, including cell division, the migration of neuros, cell differentiation and synaptogenesis — the creation of links between brain cells. Some classes of anti-depressants work by inhibiting serotonin (SSRIs and some other antidepressant classes), which will have a negative impact on the ability of the brain to fully develop and adapt in-utero.

The World Health Organization indicates that depression will be the second leading cause of death by 2020, which leads the researchers to believe that antidepressants will likely to remain widely prescribed, including during pregnancy.

Prof. Bérard added:

Our work contributes to a better understanding of the long-term neurodevelopmental effects of anti-depressants on children when they are used during gestation. Uncovering the outcomes of these drugs is a public health priority, given their widespread use.

The new study is significant because it is part of a growing body of research that suggests the events that cause autism largely occur before birth.

Concerns surrounding the use of antidepressants during pregnancy are nothing new. Earlier this year, a study showed a link between the widely used antidepressants Paxil and Prozac and higher rates of birth defects.

Some experts say non-drug treatment options, including counseling, regular and frequent exercise, meditation, acupuncture, and bright light therapy can help women manage depression during pregnancy.

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