Skyrocketing Rates of Hypertension in Pregnancy

Eye-opening findings from a study of more than 151 million US women with delivery-related hospitalizations showed that the prevalence of chronic hypertension in pregnancy rose over 13-fold between 1970 and 2010.¹

Consultant360 discussed these findings further with lead study author Cande Ananth, PhD, MPH, who shed light on contributing factors, implications for current practice, and areas in which future research is needed.

Dr Ananth is a professor, vice chair for Academic Affairs, and chief of the Division of Epidemiology and Biostatistics in the Department of Obstetrics, Gynecology, and Reproductive Sciences at Rutgers Robert Wood Johnson Medical School in New Brunswick, New Jersey.

Consultant360: What factors played a role in the skyrocketing rates of hypertension in pregnancy from 1970 to 2010?

Dr Ananth: One of the strongest factors that impacted the increase in chronic hypertension in pregnancy from 1970 to 2010 was advancing maternal age.¹ Although this is a known risk factor for chronic hypertension, my colleagues and I were surprised to see the strength of this effect. In the United States, an increasing proportion of women are electing to postpone their first pregnancy. In fact, the average age at which US women become pregnant increased by 4 to 5 years throughout the study period, which is a substantial shift in age distribution.

We also observed a persistent disparity from 1970 to 2010 between black and white pregnant patients with hypertension, which is also seen in many other obstetric complications. Pregnant black women were found to have a 2-fold higher rate of hypertension compared with pregnant white women.¹

Initially, we suspected that rates of obesity and smoking in pregnancy could have played a role in the 13-fold increase in the rate of hypertension during pregnancy, as obesity rates have risen dramatically and smoking rates have declined in the United States within the past few decades. However, following adjustment for these factors, we were surprised to find that secular changes in neither obesity nor smoking had any effect on trends in chronic hypertension among pregnant women.¹ That leaves us with a key question: what other factors are responsible for this dramatic increase in prevalence? This has yet to be determined.

C360: Could identifying contributing factors in future research initiatives be complicated by difficulty in establishing a cohort of pregnant patients, since pregnancy is a very temporary condition?

Dr Ananth: Certainly. Pregnancy has a relatively short window, and once a woman delivers her baby, everything starts anew in terms of long-term complications. What is generally missed in large population studies is when these women develop cardiovascular complications, and whether these complications are related to their pregnancy. These kinds of studies are lacking, but it will be very difficult to establish a cohort of even 1000 women during pregnancy and to follow them over time to measure these outcomes later in life.

The famous National Children’s Study–which was pursued by the National Institutes of Health and Centers for Disease Control and Prevention following Congressional authorization of the Children’s Health Act of 2000–was developed with the initial aim of studying 100,000 US pregnant women and their newborn babies over a longitudinal follow-up period of 21 years. Unfortunately, that study is now completely defunct.

On the contrary, Norwegian, Danish, and Chinese researchers have been very successful in establishing large cohorts of pregnant women and gaining valuable follow-up data on long-term cardiovascular and cerebrovascular complications in women with history of obstetrical complications.^2,3,4,5 Data from these studies are beginning to emerge, and my suspicion is that these data will be very telling 10 years from now.

C360: How might the findings from your study impact clinical practice, especially when it comes to preventing hypertension and risk stratification for hypertension-related conditions in pregnancy like preeclampsia?

Dr Ananth: Chronic hypertension in pregnancy is traditionally defined as existing hypertension upon entering pregnancy, or diagnosis of elevated blood pressure within the first 20 weeks of pregnancy. If a woman has existing hypertension prior to entering pregnancy, modifiable factors that could help greatly include reducing body mass index (BMI) if needed, mild to moderate exercise, balanced nutrition, smoking cessation, and antihypertensive medication. If hypertension is diagnosed during pregnancy, prenatal interventions involving tight blood pressure control and antihypertensive medications are all very important.

Maternal age is a non-modifiable risk factor for chronic hypertension in pregnancy, as well as conditions like preeclampsia and growth restriction of the fetus. In these patients, risk stratification is very helpful for individualized patient care.

C360: What is the key take-home message of your study?

Dr Ananth: Targeted prenatal interventions would certainly be the first step in addressing the increase in chronic hypertension in pregnancy. Controlling blood pressure, prescribing antihypertensive medications when indicated, monitoring BMI, and encouraging general healthy lifestyle behaviors are all important actions for clinicians caring for pregnant patients.

C360: What future research initiatives should be pursued as a result of these study findings?

Dr Ananth: Research initiatives dealing with risk prediction and stratification are probably the next step. Perhaps another important issue that needs to be addressed in research is long-term risk for cardiovascular disease among women who experience obstetrical complications. Although short-term data are available on cardiovascular risks following obstetrical complications, long-term data are still lacking. The general burden of cardiovascular complications and stroke has increased over time, so it will be important to understand how the increase in chronic hypertension in pregnancy contributes to the overall burden of cardiovascular complications in the United States.

—Christina Vogt

References:

1. Ananth CV, Duzyj CM, Yadava S, Schwebel M, Tita ATN, Joseph KS. Changes in the prevalence of chronic hypertension in pregnancy, United States, 1970 to 2010 [Published online September 9, 2019]. Hypertension. https://doi.org/10.1161/HYPERTENSIONAHA.119.12968.

2. Markovitz AR, Stuart JJ, Horn J, et al. Does pregnancy complication history improve cardiovascular disease risk prediction? Findings from the HUNT study in Norway. Eur Heart J. 2019;40(14):1113-1120. https://doi.org/10.1093/eurheartj/ehy863.

3. DeRoo L, Skjaerven R, Wilcox A, Klungsoyr K, Wikstrom AK, Morken NH, et al. Placental abruption and long-term maternal cardiovascular disease mortality: a population-based registry study in Norway and Sweden. Eur J of Epidemiol. 2016;31:501-511. https://doi.org/10.1007/s10654-015-0067-9.

4. Peters SAE, Yang L, Guo Y, et al; China Kadoorie Biobank collaboration group. Pregnancy, pregnancy loss, and the risk of cardiovascular disease in Chinese women: findings from the China Kadoorie Biobank. BMC Med. 2017;15(148). https://doi.org/10.1186/s12916-017-0912-7.

5. Ananth CV, Hansen AV, Elkind MSV, Williams MA, Rich-Edwards JW, Nybo Andersen AM. Cerebrovascular disease after placental abruption: A population-based prospective cohort study [Published online August 16, 2019]. Neurology. https://doi.org/10.1212/WNL.0000000000008122.