Seasonal moderators of maternal CRP levels during pregnancy

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.

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.

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.

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.