BACKGROUND Caffeine intake has been suggested to be associated with the risk of hypertension. Less is known about the associations of caffeine intake on maternal cardiovascular adaptations during pregnancy. We examined the associations of caffeine intake in different trimesters of pregnancy with repeatedly measured blood pressure and the risks of pregnancy-induced hypertension and pre-eclampsia in a population-based cohort of 7,890 pregnant women. METHODS In each trimester caffeine intake and systolic and diastolic blood pressure were assessed by questionnaires and physical examinations, respectively. Information about hypertensive complications was obtained from medical records. RESULTS Our longitudinal analyses revealed no significant differences for both systolic and diastolic blood pressure. The cross-sectional analyses showed that higher caffeine intake tended to be associated with higher systolic blood pressure in first and third trimester (P trend < 0.05), but not in second trimester. Caffeine intake was not consistently associated with diastolic blood pressure levels, or the risk of pregnancy-induced hypertension. As compared to women with caffeine intake of < 2 units/day, those using 2-3.9 units/day had a lower risk of pre-eclampsia (odds ratio 0.63 (95% confidence interval:0.40, 0.96)). CONCLUSIONS Higher caffeine intake during pregnancy seems to be associated with elevated systolic blood pressure levels in first and third trimester, but not with diastolic blood pressure levels. We did not find evidence of significant adverse associations of caffeine intake on maternal cardiovascular adaptations during pregnancy. The unexpected finding of a possible protective association with moderate caffeine intake deserves further investigation.