A new study provides some of the strongest evidence yet that using an antidepressant like Prozac, Paxil or Zoloft during the final two trimesters of pregnancy may be linked to a higher risk of autism spectrum disorder for the child, but researchers said the results should be interpreted with caution.
The research, published in JAMA Pediatrics on Monday, involved the analysis of health records in Quebec from January 1999 and December 2009. During that time 145,456 full-term singleton infants were born, and 1,054 or 0.72 percent were subsequently diagnosed with autism. The average age at first diagnosis was 4.6 years and the average age of children at the end of follow-up was 6.2 years. Boys with autism outnumbered girls 4 to 1.
Researchers identified 4,724 infants (3.2 percent) who were exposed to antidepressants in utero, with 4,200 exposed during the first trimester; 2,532 during the second and/or third trimester.
Of the first group, 40 were diagnosed with autism and in the latter group 31 were diagnosed with autism.
When taking into account maternal depression as a factor, that translates to no association for use of antidepressants in the first trimester but an 87 percent increased risk when used in the second or third trimester, Anick Bérard, a researcher at the University of Montreal, and co-authors wrote.
But other researchers not involved in the study pointed out the number of children with autism is small and that more work needs to be done before drawing such a strong conclusion.
Bérard and is team wrote that there may be several mechanisms at work that explain the phenomenon and it has to do with how serotonin impacts brain development. Scientists believe that the capacity of the brain to synthesize serotonin develops atypically in children with autism.
Due to the fact that antidepressants are "likely to remain widely used" in the future, "a better understanding of the long-term neurodevelopmental effects of [antidepressants] on children when used during gestation is a public health priority," Bérard wrote.
Doctors have long had mixed feelings about prescribing antidepressants to pregnant women. Previous studies have shown an increased risk of spontaneous abortion, prematurity and other physical issues and the U.S. Food and Drug Administration has warned that one drug, Paxil, may increase the risk of birth defects.
But many doctors have tended to weigh the harms of maternal depression — which may lead to poor nutrition, drinking, smoking, avoidance of medical care among other issues — as potentially more directly damaging to a fetus than the drugs.
The new study may shift the conversation.
"What this tells us is that we need to think even more carefully about the prenatal environment. And not just about birth defects you can see at the time of delivery but about longer-term consequences," said Susan Hyman, a former chairperson of the American Academy of Pediatrics committee on autism, who is not affiliated with the study.
Surveys have shown that the use of SSRIs in pregnant women is rising in the United States — from less than 6 percent in 1999 to 13 percent in 2003 — and Hyman emphasized that the overwhelming majority of them do not have children with autism spectrum disorders.
"We would not want people to feel guilty," said Hyman, a professor of neurodevelopmental pediatrics at the University of Rochester Medical Center. "That is something that is not productive."
Scientists believe SSRIs balance the level of serotonin, which boosts mood for the mother. But the drugs also cross the placental barrier and the effect of such drugs on the brain development of a fetus at its earliest and more vulnerable state is still being studied.
The JAMA Pedatrics research adds to the growing number of studies about antidepressant and developmental delays, autism or Attention Deficit Hyperactivity Disorder (ADHD) — but the picture is far from clear as the results have been mixed.
From a study design standpoint, the new study is stronger than some of the previous work because it is prospective, taking information about the pregnancies before they knew the outcome. But it has a number of limitations. First, the study used prescription filling data to determine which women were on antidepressants, but they may or may not have actually taken them. Perhaps more importantly, the data didn't have information about lifestyle, and it's possible that myriad factors, such as whether they smoke or their body mass index, may have influenced the findings.
Last April, Johns Hopkins University researchers reported in the journal Pediatrics that boys with autism were almost three times as likely to have been exposed to SSRIs than their typically developing counterparts. The team, which looked at nearly 1,000 mother-child pairs, found that the effect appeared to be stronger in those exposed during the first trimester and in boys than girls. A similar link was seen between a mother's SSRI use and developmental delays, but the sample was smaller and the researchers said those results should be interpreted with caution.
In another study, Harvard scientists analyzing electronic medical records reported that children who were exposed to antidepressants in the womb were at 80 percent increased risk of ADHD.
However, that same study found that children were not more likely to have autism spectrum disorders when accounting for a mother's medical history. That is, mothers with a history of psychiatric illness were more likely to have a child with autism regardless of whether or not they are on medication. Several past studies have suggested that a family history of depression may increase an individual's risk for autism.
One such study, which looked at nearly 670,000 children born in Denmark from 1996 to 2006 and used prescription information from the country's drug registry, found no association between antidepressant use and autism when researchers controlled for things like mood disorder in the mothers.
So if you're on antidepressants and pregnant or thinking about getting pregnant, what should you do?
Hyman said that it should still remain an individual decision, but that prospective mothers might want to have a serious discussion with their doctor about the possibility of other types of therapies for depression and anxiety, such as counseling.
Bryan H. King, a doctor at Seattle Children’s Hospital, had similar advice, writing in an editorial accompanying the study that "it makes no more sense to suggest that [antidepressants] should always be avoided than to say that they should never be stopped."
King added that given the fact that the prevalence of autism is on a steady upwards trajectory -- up to 1 in 45 children in the United States -- "the search for explanations, particularly among environmental factors, is critically important."
This post has been updated.
For more health news, you can sign up for our weekly newsletter here.