Prenatal Harmattan exposure and birth size: Identifying sensitive windows in pregnancy

The Harmattan season (December to March) in Western Africa is characterized by dry, dusty winds blowing from the Saharan desert towards the Gulf of Guinea, resulting in higher fine particulate matter (PM2.5) exposure; however, associations with birth size are unknown. We leveraged this seasonal variability in exposure to identify whether there are critical windows during pregnancy to Harmattan that negatively impact newborn size in a Ghanaian pregnancy cohort. The Ghana Randomized Air Pollution and Health Study (GRAPHS) enrolled 1,414 pregnant women from Kintampo, Ghana. Gestational age (GA) was established by ultrasound at enrollment; birth weight, length and head circumference were measured using standardized protocols and digital scales. We employed distributed lag models (DLMs) to examine time-varying associations between prenatal exposure to the Harmattan (yes/no) for each week gestation and birth weight, length and head circumference among infants born live > 37 weeks. DLMs also estimated cumulative effects over gestation. Models were adjusted for maternal age, parity, infant sex, ethnicity, asset index and number of antenatal visits. Analyses included n=1261 mother-infant pairs. Harmattan exposure from 3-7, 18-29, and 38-40 weeks’ gestation (Figure, panel A) was associated with lower birth weight with a cumulative effect of Harmattan over gestation on birth weight of -714 grams (95% CI -1159, -268). Separately, Harmattan exposure from 4-12 and 23-31 weeks' gestation (Figure, panel B) was associated with smaller head circumference with a cumulative effect of Harmattan over gestation on head circumference of -2.9 centimeters (95% CI -5.3, -0.5). We did not identify an association between Harmattan and birth length. These data suggest that prenatal Harmattan exposure is associated with lower birth weight and smaller head circumference. Certain gestational windows may have greater impact than others. Climate change threatens to make Harmattan more severe lending urgency to better understanding its effects on health beginning in utero.