Objective: The purpose of this study was to analyze the impact of parity and baseline body mass index on blood pressure levels in pregnancy. Study Design: We studied a longitudinal historic cohort of 166 healthy pregnant women who gave birth in 2000 to a third child at the University Hospital of Lund; blood pressure measurements were obtained at each antenatal visit during the three consecutive pregnancies. Results: The mean systolic and diastolic blood pressure levels were consistently higher during the first pregnancy at comparable weeks of gestation, significantly so during the third trimester. The body mass index correlated with diastolic blood pressure levels only in the first pregnancy, and the impact of parity on third trimester blood pressure levels was greatest in the women with a high body mass index. Age, smoking, change of paternity, or a short time interval between pregnancies did not influence blood pressure levels. Conclusion: The interrelationship among blood pressure levels, parity, and body mass index in normal pregnancy resembles the situation in hypertensive pregnancies, which implies common adaptive mechanisms. (Am J Obstet Gynecol 2002;187:1343-8.)