This study uses data from the NHANES 1999 to 2008 sample to define the prevalence and risk factors for hypertension for women of reproductive age in the United States, and to describe the relative prevalence of the medications used to treat hypertension in this group. We report an overall hypertension prevalence of 7.7%, which was relatively stable across the 10-year study period. Advancing age, non-Hispanic black race/ethnicity, diabetes, chronic kidney disease, and obesity were independently associated with hypertension in this population. An estimated 4.9% of women of reproductive age used antihypertensive pharmacologic therapy. Among anti-hypertensive users, the most common medication classes included diuretics (47.9%), ACE inhibitors (44.0%), and beta blockers (23.3%).
The most significant modifiable risk factor for hypertension that we identified in our analysis was obesity. After adjustment for other variables, women with class I obesity were approximately 4-fold and women with class II/III obesity approximately 6-fold more likely to be hypertensive than their normal weight counterparts. As shown in , we also observed that the prevalence of hypertension increased in a near linear fashion with BMI and only started to plateau as BMI approached 40. The rising prevalence of obesity in pregnancy,
suggests obstetricians will be increasingly confronted with the issues of hypertension.
Non-Hispanic Black race/ethnicity and advancing age were non-modifiable patient characteristics associated with increased risk for hypertension. Multiple studies in the general population have demonstrated that hypertension in blacks is more prevalent, earlier in onset, and more severe 
. Hypertension, in part, contributes to the large disparities between white and blacks in the US in rates of cardiovascular disease 
and adverse pregnancy outcomes 
. Developing preventive measures for hypertension aimed at this group may be one mechanism to help decrease these disparities. It should be noted that nearly one-half of young black women were obese in this sample; preventative measures might consider targeting obesity in this population.
The increased prevalence of hypertension with advanced age, likewise, may explain some of the increased risk for some pregnancy complications in women of advanced maternal age. The problem of chronic hypertension in pregnancy is likely to become more common as the numbers of mothers of advanced age increases 
Approximately 5% of women of reproductive age took antihypertensive medications. Most common among these were diuretics, ACE inhibitors, and beta blockers. Recent data regarding the risks of congenital malformations associated with antihypertensive exposure during the first trimester have been mixed, with some studies reporting increased risk while others suggest that any observed risk is attributable to the underlying hypertension (“confounding by indication”) 
. The Food and Drug Administration currently categorizes most antihypertensives as category C–meaning that animal studies either show an adverse effect or are lacking and no well-controlled human studies exist, and that medication should only be given when the benefit justifies the potential risk to the fetus 
. As about half of all pregnancies in the United States are unintended 
, medications prescribed to women of reproductive age are likely to be frequently taken during the first trimester. Given the high prevalence of antihypertensive medication utilization in women of reproductive age, further research into the safety of these medications in pregnancy is merited to inform the selection of the safest antihypertensive for this population.
We found a relatively stable rate of hypertension across the study period. Data suggest that the rate of obesity in the U.S. has begun to plateau 
. As shown in our study, obesity is an extremely important risk factor for hypertension in this population, and the lack of rise in obesity rates may explain the lack of rise in the prevalence of hypertension.
Results reported in this study should be interpreted with the following limitations in mind. First, there are several patient characteristics that are known to be associated with hypertension from previous studies, including heavy alcohol use 
, OCPs use 
, and cigarette smoking 
, which were not significant in our analysis of the NHANES sample. It may be that the effect of alcohol and smoking in contributing to hypertension occurs only after many years of exposure and thus the association is less robust in young women, such as those considered in our study or that some women with hypertension avoid tobacco and alcohol. In this study, OCP use in the univariate analysis was protective; however, OCP use was inversely correlated with advancing age, and after adjustment for this and other patient characteristics, OCP use was not significantly associated with hypertension. It is also likely that clinicians are reluctant to prescribe OCP to hypertensive women or discontinue OCPs if women develop hypertension, which would lead to a lack of association or even an inverse association. An additional limitation is that the lower age limit considered is 20 (as certain variables of interest are not reported in the NHANES for younger women). Likewise, in keeping with most epidemiologic studies of women of reproductive age, we defined the upper age limit for our population at 44–but women older than this can become pregnant through assisted reproduction, and hypertension is likely even more prevalent in this group. We were not able to analyze the effect of physical activity on the risk of hypertension, as the questions used to ascertain activity changed during the study period. Finally, NHANES is a cross-sectional study and it is appropriate for describing prevalence of conditions and associations, but not temporal relationships. As with any observational study, it has a limited role in establishing causality.
In conclusion, hypertension occurs in about 8% of women of reproductive age. Obesity is a risk factor of particular importance in this population because it affects over 30% of young women in the U.S., is associated with more than a 4 fold increased risk of hypertension, and is potentially modifiable. There are also remarkable differences in the prevalence of hypertension between racial/ethnic groups. Women of reproductive age are commonly exposed to antihypertensive medications and data regarding the fetal risks associated with first trimester exposure are conflicting; as a large proportion of pregnancies are unplanned, further work is needed to define the safest antihypertensive medications for these patients.