Hypertensive Disorders of Pregnancy on the Rise in Canada

Hypertensive disorders of pregnancy (HDPs)—including preexisting (chronic) hypertension, gestational hypertension, and preeclampsia or eclampsia—have increased by about 40% over the last decade in Canada, according to results of a retrospective population-based study published in the Canadian Medical Association Journal and discussed further in an accompanying editorial.^1,2 HDPs area leading cause of severe maternal morbidity, and in Canada, severe preeclampsia was the most common contributor to this morbidity between 2012 and 2016.

Rates of some severe adverse pregnancy outcomes associated with untreated hypertension,however, are down, thanks to increasedearly recognition and treatment, improved blood pressure management, and timing of births among women at risk of or already affected by an HDP.^1,2 The outcomes experienced at lower rates includeearly preterm delivery, intrauterine fetal death, maternal hospital stay of 7 days or longer, admission to the maternal intensive care unit, and severe hemorrhage.

But among females with any HDP, rates of cesarean delivery rose from 42% in 2012 to 44.3% in 2021, as did rates of acute renal failure, from 0.4% to 0.6%. In the case of the latter, a contributing factor could be changes in how preeclampsia is managed, posited the team. That includes better blood pressure control and, sometimes, delayed delivery, which could permit ongoing reduced renal blood flow and worsen glomerular filtration, they said.

Early recognition of pregnancy-related hypertension has led to reduced rates of preterm delivery severe hemorrhage, and intrauterine fetal death in Canada | Image Credit: peopleimages.com - stock.adobe.com

The investigators found that among 2,804,473 hospital admissions for birth between 2012 and 2021 in Canada, excluding the province of Quebec, the rate of any HDP increased from 6.1% to 8.5%, including preexisting hypertension (0.6% to 0.9%), gestational hypertension (3.9% to 5.1%), and preeclampsia (1.6% to 2.6%).

This is despite the fact that advances in preventing and managing HDPs are known and utilized, including use of low-dose acetylsalicylic acid prophylaxis against early-onset preeclampsia in women at increased risk.

Why, exactly, have these rates of HDPs risen? The authors explored possible reasons. Many HDP risk factors have been previously identified, they noted.

“Of those we explored, the proportion of females in rural areas remained unchanged and the proportion of multiple pregnancies decreased,” they wrote, “while the proportions of females with advanced maternal age, nulliparity, and preexisting diabetes increased.”

By their calculations, however, adjusting for all of these factors didn’t significantly attenuate the higher odds of HDPs over time. They then suggested that other factors that they didn’t account for might explain the rise in HDPs, such as body mass index (BMI), which is known to be a risk factor for hypertension in pregnancy.

Previous US work, however, shows that obesity trends “could not explain” the rising rates of chronic hypertension in pregnancy between 1970 and 2010.

The fact remains that BMI is increasing rapidly in Canada, so the association between BMI and HDPs deserves more study, said the authors. Between 2015 and 2021, among females aged 18 to 34 years, the proportion of those who were overweight or obese rose from 41% to 48%, and for those aged 35 to 49 years, from 56% to 64%. The results of this study also showed that provinces with higher rates of obesity, such as New Brunswick and Newfoundland and Labrador, indeed had higher rates of HDPs.

The HDP rate is increasing in the US as well as in Canada. In this country, from 2007 to 2019, incidence of new-onset HDPs rose from 3.7% to 7.7% in rural areas and from 4.9% to 8.4% in urban regions.³ However, in many other Western nations, trends in HDPs are stable or downward—another trend worthy of investigation, said the authors.

References

1. Dzakpasu S, Nelson C, Darling EK, et al; the Canadian Perinatal Surveillance System. Trends in rate of hypertensive disordres of pregnancy and associated morbidities in Canada: a population-based study (2012-2021). CMAJ. 2024;196(26):E897-E904. doi:10.1503/cmaj.231547

2. Varner C. Optimizing postpartum care in Canada as rates of comorbidity in pregnancy rise. CMAJ. 2024;196(26):E908-E909. doi:10.1503/cmaj.241017

3. Cameron NA, Everitt I ,Seegmiller LE, Yee LM, Grobman WA, Khan SS. Trends in the incidence of new-onset hypertensive disorders of pregnancy among rural and urban areas in the United States, 2007 to 2019. J Am Heart Assoc. 2022;11(2):e023791. doi:10.1161/JAHA.121.023791