Antidepressant use in pregnancy linked to language development
Taking a common class of antidepressants called serotonin reuptake inhibitors, or SRIs, during pregnancy alters the developmental time-course of the child’s language processing, according to a new study published Monday in the Proceedings of the National Academy of Sciences.
While the results are striking, they hardly suggest the practice should be stopped: The researchers found that the children of women who are depressed while pregnant and who do not take medication are also born with an altered course of development.
Between 15% and 20% of women develop mood disorders while pregnant, and 5% to 13% of women are treated with an antidepressant, the study says. Previous research in animal models has revealed some changes in brain development among the offspring of animals given such medications, raising fears that they might also be causing changes in humans.
In the new study, conducted by a well-known team of developmental researchers led by Janet Werker of the University of British Columbia and Takao Hensch of Harvard, three groups of expectant mothers were studied: mothers who had no mood disorder, mothers who had gestational depression but did not take medication, and mothers who had gestational depression and did take medication.
To study the effects of depression and medication on the infants, the researchers used three different tasks. First, they used a vowel and consonant discrimination task that boldly goes where you might have thought it impossible for scientists to go: They studied consonant and vowel discrimination ability in the womb, at 36 weeks.
The researchers accomplished this by placing a speaker up against the mother’s belly while measuring the fetus’ heartbeat. If the heart rate changes when the task changes from one consonant to another or one vowel to another, that is taken to mean the fetus was able to discriminate between the sounds. Most infants are able to discriminate vowels at 36 weeks but not consonants.
The scientists also used another task when the children were 6 months and 10 months old. The task takes advantage of the difference between our natural-born auditory capabilities and the changes that occur as we develop. Research has shown that until children are 8 months old, they are able to discriminate between the sound “da” as it is spoken in Western languages and a Hindi variant. But because non-Hindis do not hear the Hindi variant, they quickly lose that ability at about 8 months.
The researchers found that the children born to non-depressed mothers behaved just as expected based on previous studies: They discriminated vowels but not consonants in the womb, and, out of the womb, they perceived a difference between a Western “da” and a Hindi “da” at 6 months but not at 10 months. Among the children of SRI-treated mothers, however, there was no difference between the “da’s” at either 6 or 10 months. That suggests the children of SRI-exposed mothers had accelerated language-processing development.
And the same was true in the womb — SRI-exposed fetuses discriminated both vowels and consonants at 36 weeks.
This acceleration contrasts with the children of mothers who were depressed but did not take antidepressants. Those fetuses did not act any different in the womb but instead of discriminating “da”s at six months, they discriminated them at 10 months, something not seen in normal development. This suggests depression without medication leads to developmental delay, the authors write.
The findings indicate that SRI treatment and untreated depression have opposite effects on development: SRI treatment accelerates it, while untreated depression delays it. The researchers speculate this may be because SRIs are influencing how plastic, or changeable, the infant’s brain is at any given time. Depression may have the opposite effect, since it is also believed to involve the serotonin system.
The authors stress that neither course is good. While accelerated development may sound better, language skills progress on a finely tuned schedule. Our brains go through important developmental periods in which they are particularly sensitive to their environments; one would not want a language period, for example, to occur while the infant is still in the womb. So interrupting, accelerating or slowing down this schedule may have equally deleterious effects on later life.
As a result, the take-away is neither that depressed expectant mothers should nor should not take medication. Rather, it’s that brain development is a carefully calibrated process that can easily be upset; sometimes there are no easy solutions. More research into just how this takes place may help expectant mothers make these difficult decisions.
You can read a summary of the study here.
Return to the Science Now blog.
