We sought to perform a tree-based analysis of lifestyle risk factors for hypertension in pregnancy (HP) with univariate and multivariate analyses. Seventy-eight HP patients and 199 normal controls were recruited from primiparous women 20 to 34 years of age. Data from angiotensinogen (AGT) genotyping and data from a self-administered questionnaire about lifestyle were subjected to univariate and multivariate analyses. By dividing the subjects into two subgroups--those who possessed "the TT genotype of AGT" and "body mass index (BMI) < 24" and those who did not--we were able to examine the acquired risk factors for HP during pregnancy in these two groups. Multivariate analysis selected "mentally stressful condition" and "no antenatal training during pregnancy" in the former group, and "poorly balanced diet" in the latter group. Determination of factors obvious before pregnancy, such as genotype or prepregnancy BMI, may be useful for devising effective individualized strategies for preventing HP.