A small proportion of women suffering from chronic nephritis had eclampsia. For the most part, autopsy will reveal the presence of renal changes usually of acute nephritis, though occasionally it may be engrafted upon a chronic process.
—J. Whitridge Williams (1903)
At the time of Williams Obstetrics’ first edition, little attention was paid to blood pressure changes, even with “toxemia.” At that time, chronic hypertension was designated “senile” and thought to develop only in older individuals (Lindheimer, 2015). Indeed, chronic hypertension is not mentioned, per se, in Williams’ 1903 textbook, except for some deference given to chronic anatomical renal changes occasionally associated with eclampsia.
It is now apparent that chronic hypertension is one of the most common serious complications encountered during pregnancy. This is not surprising because, according to the National Health and Nutrition Examination Survey (NHANES) from the Centers for Disease Control and Prevention (2011), the prevalence of hypertension in women aged 18 to 39 years approximates 7 percent.
The incidence of chronic hypertension complicating pregnancy varies depending on population vicissitudes. In a study of more than 56 million births from the Nationwide Patient Sample, the incidence was 1.8 percent (Bateman, 2012). And, in more than 878,000 pregnancies from the Medicaid Analytic Extract, 2.3 percent were complicated by chronic hypertension (Bateman, 2015). Despite this substantive prevalence, optimal management has not been well studied. It is known that chronic hypertension usually improves during early pregnancy. This is followed by variable behavior later in pregnancy and, importantly, by the unpredictable development of superimposed preeclampsia. The latter carries increased risks for maternal and perinatal morbidity and mortality.
To define chronic hypertension, the range of normal blood pressure must first be established. This is not a simple task because, like all polygenically determined biological variants, blood pressure norms differ between populations. And, within these norms, wide variations are found between individuals. Moreover, numerous epigenetic factors influence presentation. For example, not only do blood pressures vary between races and genders, but pressures—especially systolic—rise directly with increasing age and weight. Thus, pragmatically, normal adults have a broad range of blood pressures, but so do those with chronic hypertension. And finally, resting blood pressure measurements do not reflect daily activities.
After these variables are acknowledged, important considerations for any population are the attendant risks of chronic hypertension. It is a leading cause of death and accounts for nearly 15 percent of mortality worldwide. Approximately 65 million Americans have hypertension, and this number is growing concurrently with epidemic obesity (Kotchen, 2015). Hypertension increases substantively the risk of cardiovascular disease, coronary heart disease, congestive heart failure, stroke, renal failure, and peripheral arterial disease (Forouzanfar, 2017).
Definition and Classification
For the foregoing reasons, chronic hypertension would logically be defined as some level ...