Association between C-reactive protein response to influenza vaccine during pregnancy and birth outcomes.

Objective: A growing body of evidence suggests inflammatory markers can help predict poor outcomes in pregnancy. We evaluated C-reactive protein (CRP)-a key biomarker of inflammation-before and after a safe immune provocation (the seasonal influenza vaccine) during pregnancy. We evaluated predictors of the magnitude of response, as well as the association between CRP response and birth outcomes.

Methods: Nonrandomized prospective cohort trial measuring CRP before and 3 days after administering seasonal flu vaccine to low-risk obstetrical patients in Calgary, Alberta.

Results: We analyzed 27 prevaccination/postvaccination samples. Body mass index (BMI) was positively associated with CRP at Day 0, and women with higher prepregnancy BMI had a less robust response to vaccination than did leaner women. There was a strong positive association between CRP response and infant birth weight; women who had the greatest response to vaccination (by tertile) gave birth to babies that weighed, on average, 256.2 g more than babies born to women with the lowest response.

Conclusions: Higher BMI in pregnant women was associated with higher baseline CRP and less pronounced CRP response to vaccination. Stronger CRP response was associated with higher birth weight. These findings underscore the potential value of a more dynamic approach to studying the regulation of inflammation during pregnancy and its implications for birth outcomes. This study was registered as a clinical trial in clinicaltrials.gov (ID: REB15/1418).