Infants whose mothers have taken SSRI antidepressants are more likely to have decreased birth weight, gestational length

The results showed, once adjusted for socio-demographic and familial factors, that infants exposed to SSRIs during two or more trimesters weighed 205 grams less than infants whose mothers were not exposed to any antidepressants. The infants would also be born 4.9 days earlier, on average. However, co-author of the study Katerina Nezvalova-Henriksen commented that, "the biological mechanisms by which long term SSRIs exposure may affect birth weight remain unknown."

"Severe depression or depression not responding to non-pharmacological therapy may negatively affect the course of pregnancy and the pre- and post-partum period," Dr Nezvalova-Henriksen explained. "The risks and benefits of SSRI therapy should therefore be carefully evaluated in each individual case."

Researchers from Norway and Canada used data from The Norwegian Mother and Child Cohort Study (MoBa) and The Medical Birth Registry of Norway to measure the effect of SSRIs and maternal depression on birth weight and gestational length, using their sibling design method to differentiate the study from previous studies looking into prenatal SSRI effects.

27,756 siblings were included in the study, 194 of which were prenatally exposed to SSRIs. By applying the sibling design, the researchers were able to address the unmeasurable and unknown family-level differences that may have been a source of bias. The study was divided into a group where women used SSRIs during pregnancy and a group that did not use any antidepressants. The reasons for women taking SSRIs included not only depression and anxiety but also other neuropsychiatric disorders. 7450 mothers in the data from MoBa had a lifetime history of major depression.

The study concluded that neither shared genetics nor family environment can explain the associations between exposure to SSRIs and birth weight.