Abstract
BACKGROUND: Hypertensive disorders of pregnancy (HDP) are associated with increased long-term risk of both maternal and offspring cardiovascular disease. The incidence of HDP has increased concurrently with the upward shift in maternal age distribution; however, the association between changes in maternal age distribution and rates of HDP in the US is unknown. METHODS: Data from 2011 to 2021 were abstracted from the National Center for Health Statistics, which includes all live births in the United States. Births to individuals aged 15 to 44 years were included, given that 99% of all births occur in this reproductive age group. HDP was coded as yes/no and included both gestational hypertension and preeclampsia. We described changes in HDP per 1000 live births between 2021 and 2011 by calculating rate ratios. We then decomposed the change in frequency of HDP with the Kitagawa technique into the 2 rate change components: (1) change in maternal age distribution and (2) change in age-specific HDP rates (ie, the incidence rate at a given age). RESULTS: In 2011 and 2021, there were 7 595 018 live births that occurred. The mean maternal age increased from 27.9 (6.1) to 29.9 (5.7) years. The frequency of HDP increased significantly from 43.8 (43.6-44.0) to 90.9 (90.6-91.2) per 1000 live births from 2011 to 2021. The Kitagawa decomposition revealed that the change in maternal age distribution had no association with the increased rate of HDP (0.0 [-0.1 to 0.1]). Conversely, the age-specific rate of HDP increased across all age groups and was responsible for the total change in HDP (47.1 [46.7-47.4]). CONCLUSIONS: Although both maternal age and frequency of HDP increased significantly between 2011 and 2021, the higher rates of HDP were not due to the upward shift in the age distribution, but rather, to increases in HDP frequency within all age groups.