Being diagnosed with pregnancy induced hypertension (HTN) may result in the development of post-pregnancy hypertension in the years following the delivery.
Hypertension (HTN), or commonly high blood pressure, is a medical condition where there is persistent elevation in the blood pressure in the arteries. If this persists long-term the body may suffer direct damage in the form of stroke, peripheral vascular disease, and even heart failure. Hypertensive disorders of pregnancy affect up to 10% of pregnancies and include several conditions such as pre-eclampsia; eclampsia; hemolysis, elevated liver enzymes, low platelets (HELLP) syndrome, and gestational hypertension. Both the American Heart Association and the European Society of Cardiology consider the disorders of pregnancy induced hypertension as risk factors for cardiovascular diseases (i.e. ischemic heart disease and stroke) in women. The precise amount of time it takes to develop HTN in women who experience one of these disorders during their pregnancy remains unclear.
In a recent study published in the BMJ, Behrens and colleagues investigated the amount of time it took from delivery to develop HTN in women who experienced pregnancy induced hypertension. Specifically, they were interested in exploring the increased risk of developing HTN in these women and how the risk evolved over time. The primary outcome measured in this study was the number of new cases of post-pregnancy HTN requiring treatment with prescription medications and hazard ratios in 10 the years following delivery.
Using the Danish civil registration system data was collected using the personal identification number that is assigned to all Danish residents. The researchers used the medical birth register and identified two cohorts. The first cohort was reflective of the cumulative incidences of post-pregnancy HTN and identified all women having a first pregnancy lasting 20 or more weeks and ended in a live birth or stillbirth between 1995-2012. The second cohort estimated the hazard ratios for post-pregnancy HTN and identified all women who had at least one pregnancy that lasted 20 or more weeks, ending in a live birth or stillbirth between 1978-2012, and who lived in Denmark during the follow-up period, 1995-2012. Women who used antihypertensive drugs before their first pregnancy or up to 20 weeks gestation in that first pregnancy were deemed to have pregestational HTN and were excluded from both cohorts.
In the 10 years following delivery women who had normal blood pressures in their first pregnancy during their 20s, 30s, or 40s had cumulative new cases of HTN of 4%, 5.7%, 11.3%, respectively. The researchers reported that 14-32% of women who experienced pregnancy induced hypertension during their first pregnancy developed HTN in the 10 years following their delivery and their rates of HTN remained doubled more than 20 years later compared to 4-11% of women with normal blood pressures in their first pregnancy.
Of women with a hypertensive disorder of pregnancy in the first pregnancy in their 20s, 14% developed hypertension in the first-decade post partum, compared with 4% of women with normotensive first pregnancies in their 20s. The corresponding percentages for women with a first pregnancy in their 40s was 32%. In the year after delivery, women with pregnancy induced hypertension had 12-fold to 25-fold higher rates of hypertension than did women with a normotensive pregnancy. Rates in women with a pregnancy induced hypertension were threefold to 10-fold higher 1-10 years post-partum and remained twice as high even 20 or more years later.
The strength of this study lies in the very large cohort which all but eliminated selection bias and the study design which eliminated recall bias. One limitation of this study was the risk of other factors affecting blood pressure such as salt intake, stress, and alcohol use. The researchers were also not able to exclude the possibility that body mass index may affect the association between post-pregnancy HTN and hypertensive disorders of pregnancy.
This study is important because it gives clinicians for the first time a clear picture of the risk of developing hypertension in women previously diagnosed with pregnancy induced hypertension. Being able to predetermine the hypertensive risk after an experience of pregnancy induced hypertension will better allow physicians to diagnose and care for these patients as early as possible. The authors recommend that cardiovascular disease prevention in women with pregnancy induced hypertension should include blood pressure monitoring initiated soon after pregnancy.
Written By Kimberly SpencerB.Sc. (Hons)
Behrens, Ida et al. “Risk Of Post-Pregnancy Hypertension In Women With A History Of Hypertensive Disorders Of Pregnancy: Nationwide Cohort Study.” BMJ, 2017, p. j3078. BMJ, doi:10.1136/bmj.j3078.