Increased incidence of hypertensive disorders of pregnancy in young Americans

Hypertensive disorders of pregnancy (HDP), which include preeclampsia, eclampsia, and hypertension, are leading causes of mortality and morbidity in pregnant individuals. As a result, HDP has become a significant health crisis among pregnant individuals in the United States.

Recent data indicates that HDP is an important risk-enhancing factor of cardiovascular disease. HDP has been shown to increase the risk of heart failure by two- to four-fold in pregnant women.

Study: Association of Birth Year of Pregnant Individuals With Trends in Hypertensive Disorders of Pregnancy in the United States, 1995-2019. Image Credit: Compoo Suriyo / Shutterstock.com

Background

In the past decade, the rate of HDP has almost doubled to 8% of pregnant women. The highest incidence of HDP has been reported among non-Hispanic American Indians, non-Hispanic Black individuals, and Alaska Native individuals. 

Although pregnant individuals’ age at their first birth is a risk factor for HDP, a recent study has shown that women of all ages are increasingly affected by this condition. This observation strongly indicates that factors aside from age contribute to the incidence of HDP.

A recent JAMA Network Open study performed an age-period-cohort analysis to investigate the independent relationship between the age of pregnant women at delivery, the birth year of pregnant individuals (cohort), and year of delivery (period) with new onset of HDP among nulliparous individuals. 

About the study

A total of 38,771,194 nulliparous individuals between the ages of 15 and 44 were identified between 1995 and 2019. Individuals without enough relevant data on HDP and pre-pregnancy hypertension were excluded from the cohort.

Finally, 38,141,561 individuals were included, of which 20.2% were Hispanic, 6.5% non-Hispanic Asian or Pacific Islander, 0.8% non-Hispanic American Indian or Alaskan Native, 57.8% non-Hispanic White, and 13.9% non-Hispanic Black.

Study findings

The cohort analysis revealed that the incidence of new-onset HDP was higher in pregnant women of an older age at delivery, in more recent periods, and in more recent birth years of pregnant individuals. Compared to nulliparous pregnant individuals born in the 1950s, those born in the 1990s and 2000s had a higher incidence of HDP, even after adjusting for age at delivery. 

A persistent occurrence of HDP, irrespective of age, birth cohort, and delivery period, was observed among self-identified non-Hispanic American Indian or Alaska Native and non-Hispanic Black individuals. In addition, a significant increase in HDP incidence in these groups was reported from 2010 to 2019. 

The study findings add to previously published data by establishing an independent relationship between a birth cohort of pregnant women and the incidence of HDP among nulliparous individuals in the U.S. between 1995 and 2019.

Although the current study did not identify factors responsible for the incidence of HDP in younger pregnant women, it highlighted some possible contributing factors.

For example, pregnant women with a history of cardiovascular disease were at an increased risk of developing HDP. This factor also increased mortality and morbidity rates, as well as the risk of cardiovascular health issues for the offspring. The cohort analysis also revealed a tendency for greater onset of new HDP among older and non-Caucasian pregnant individuals at delivery.

A previous Hyperglycemia and Adverse Pregnancy Outcome Study reported that individuals with a cardiovascular health issue at a mean gestational age of 28 weeks are nine times more susceptible to developing preeclampsia as compared to those without cardiovascular disease.

Among cardiovascular health-related issues, the incidence of obesity has significantly increased from 6.2% between 1976-1980 to 32.7% between 2017 and 2018. However, the population-attributable fraction for HDP associated with obesity has not changed considerably between 2011 and 2019. This suggests that obesity could partially contribute to the incidence of HDP.

More research using pregnancy-specific cohorts with long-term follow-up is needed to understand the association between obesity and HDP better.

Study limitations 

The potential misdiagnosis of new-onset HDP from the National Vitals Statistics System (NVSS) records were noted. However, due to the inclusion of individuals who experienced preeclampsia and gestational hypertension, issues associated with the change of HDP definition were sorted.

As the study is ecological in nature, the potential risk factors for HDP were not identified.

Conclusions

Elevated rates of HDP in younger pregnant individuals from more recent generations have increased the urgency to develop effective strategies to prevent adverse clinical outcomes. Studies such as the current one have increased awareness among practitioners about the prevalence of HDP in younger generations to ensure that proper preventive measures are advised.

Early assessment of cardiovascular health and the initiation of effective treatments prior to an individual’s first pregnancy could be an effective strategy for reducing the incidence of HDP.

Multidisciplinary experts, including primary care physicians, obstetrician-gynecologists, and cardiologists, must work together to develop strategies for the optimal management of HDP risk factors before, during, and after pregnancy.

Journal reference:

  • Cameron, N. A., Petito, L. C., Shah, N. S., et al. (2022) Association of Birth Year of Pregnant Individuals With Trends in Hypertensive Disorders of Pregnancy in the United States, 1995-2019. JAMA Network Open 5(8). doi:10.1001/jamanetworkopen.2022.28093