Seasonal moderators of maternal CRP levels during pregnancy.

Background: The human immune system is highly susceptible to seasonal changes, however it is unknown whether this holds true during pregnancy. This study assessed whether C-Reactive Protein (CRP) levels are moderated by season of sample collection and/or a person's tendency to have low mood during the fall-winter months (Seasonal Affective Disorder or SAD) in a Canadian pregnancy and birth cohort. As overweight/obesity has been associated with both elevated CRP and fall-winter SAD, the moderating effect of overweight/obesity on these seasonal effects was also examined. Methods: Maternal plasma CRP was measured at weeks 11-19 and 24-30 of pregnancy. Separate Generalized Linear Models were used to predict these two CRP levels using a 2 season of collection (fall-winter vs. spring-summer) by 2 seasonal group (yes/no for lifetime SAD) by 2 pre-pregnancy BMI group (healthy weight vs. overweight/obese) design. Results: A significant 3-way interaction predicted CRP levels at pregnancy weeks 24-30 (F = 8.49, df = 1, 353, p = .004), with the highest levels in mothers with the combination of fall/winter plasma sampling, meeting screening criteria for lifetime SAD, and being overweight/obese. The respective 2-way season of sampling by BMI group interaction was also highly significant (F = 8.18, df = 1, 353; p = .004). Unexpectedly, these various results were independent of state depression and maternal anti-depressant use. No seasonal differences were found for early pregnancy CRP levels. Conclusions: Overweight/obese mothers had greater fall/winter increases in later pregnancy CRP levels than did healthy weight mothers, further boosted by a maternal history of fall-winter SAD. Both environmental and individual-level seasonality may be critical considerations for future research on gestational inflammation.