We estimated changes in the prevalence of chronic hypertension among pregnant women and evaluated the extent to which changes in obesity and smoking were associated with these trends. We designed a population-based cross-sectional analysis of over 151 million women with delivery-related hospitalizations in the United States, 1970 to 2010. Maternal age, year of delivery (period), and maternal year of birth (birth cohort), as well as race, were examined as risk factors for chronic hypertension. Prevalence rates and rate ratios with 95% CIs of chronic hypertension in relation to age, period, and birth cohort were derived through age-period-cohort models. We also examined how changes in obesity and smoking rates influenced age-period-cohort effects. The overall prevalence of chronic hypertension was 0.63%, with black women (1.24%) having more than a 2-fold higher rate than white women (0.53%; rate ratio, 2.31; 95% CI, 2.30-2.32). In the age-period-cohort analysis, the rate of chronic hypertension increased sharply with advancing age and period from 0.11% in 1970 to 1.52% in 2010 (rate ratio, 13.41; 95% CI, 13.22-13.61). The rate of hypertension increased, on average, by 6% (95% CI, 5-6) per year, with the increase being slightly higher among white (7%; 95% CI, 6%-7%) than black (4%; 95% CI, 3%-4%) women. Adjustments for changes in rates of obesity and smoking were not associated with age and period effects. We observed a substantial increase in chronic hypertension rates by age and period and an over 2-fold race disparity in chronic hypertension rates.