Objectives Aim of this study was to investigate the associations of C-reactive protein levels, as marker of low-grade inflammation, with blood pressure development during pregnancy and the risks of gestational hypertensive complications. We also explored the role of maternal BMI in these associations. Methods High-sensitivity C-reactive protein levels were measured in early pregnancy (median 13.2 weeks, 95% range 9.6-17.6) in 5816 mothers participating in a population-based prospective cohort study in the Netherlands. Blood pressure measurements were performed in each trimester. Information about pregnancy-induced hypertension and preeclampsia was retrieved from hospital charts of the women. Results Longitudinal analyses showed that C-reactive protein levels were not associated with SBP and DBP patterns throughout pregnancy. Trimester-specific multivariate linear regression models showed that as compared to low C-reactive protein levels (<5.0 mg/l), elevated levels (>= 20.0 mg/l) were associated with maternal SBP and DBP. Elevated C-reactive protein levels in early pregnancy were associated with the risks of pregnancy-induced hypertension [odds ratio (OR) 2.78, 95% confidence interval (CI) 1.66-4.66]. After adjustment for maternal BMI, all associations attenuated. Conclusion Our results suggest that first-trimester C-reactive protein levels are associated with SBP and DBP levels throughout pregnancy and with gestational hypertensive complications, but these associations are largely explained by maternal BMI. J Hypertens 29: 2413-2421 (C) 2011 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.