A new model to study season-of-conception effects on child neurodevelopment based on maternal history of seasonal affective disorder.

Season of birth/conception has been used to study neurodevelopmental risk in hundreds of studies, however the translational impact of this work remains limited. We propose a new model to study season-of- conception effects on neurodevelopment using maternal fall-winter seasonality as a key moderating variable, and provide initial empirical data to support this new approach. In an ongoing pregnancy cohort study we evaluated associations between season-of conception and maternal history of fall-winter Seasonal Affective Disorder (SAD) on child executive functioning in 520 children at age 54 months. Executive functioning was measured using computerized administration of the Flanker test (a measure of attention) and the Dimensional Change Card Sort (a measure of cognitive flexibility). Results indicated that sixty-four mothers (12.3 %) met criteria for historical fall-winter SAD. MANCOVA found a significant season of conception (fall-winter vs. spring-summer) by maternal SAD (yes/no) by sex (female/male) interaction predicting the two child outcomes (F = 4.11, df= 2,509, p=.017). In the subgroup of children in the SAD group, girls conceived in the fall-winter vs. spring-summer months had significantly lower scores on the Dimensional Change Card Sort. No significant effects related to season of conception and/or maternal SAD were found in boys. Similar results were found after controlling for maternal depressive symptoms during pregnancy. In summary, season-of-conception was associated with impaired child executive functioning at age 54 months, but only in girls of mothers with a history of fall-winter SAD. The use of maternal seasonality and sex as moderating variables may be critical to early neuro- developmental research based on pregnancy timing, particularly at more northern latitudes.