Hypertension in Pregnancy

Michael Belfort, S. Thorton, George Saade, Michael Belfort, S. Thorton, George Saade

• Editorial: CRC Press
• Año: 2002
• ISBN:
  9781135564216
• Edición: 1
• Categoría: Medicina
• Categoría: Teoría, práctica y referencia médicas

Covers gestational and chronic hypertension in addition to severe preeclampsia, eclampsia, and HELLP syndrome and discusses the interaction with the renal, hematological, neurological, and hepatic systems of pregnant women.

1
Diagnosis and Classification of Preeclampsia and Other Hypertensive Disorders of Pregnancy

Mark A. Brown
St. George Hospital and University of New South Wales, Sydney, New South Wales, Australia

I. INTRODUCTION

The diagnostic criteria for disorders of hypertension in pregnancy are not currently uniform and there are a number of different systems promulgated by major working groups and international societies. There has been some progress toward unifying the classification and the major consensus statements now agree on most of the terminology. As for preeclampsia, the two extremes of the diagnostic spectrum take either a “restrictive” or an “inclusive” approach. The former requires both de novo hypertension after 20 weeks and the presence of proteinuria > 300 mg/24 hours, while the latter assumes that preeclampsia is a multisystem disorder and a diagnosis of preeclampsia is based upon symptoms and signs in the organs commonly affected in this condition. Proponents of the restrictive concept argue that broadening the definition includes women who may not have true preeclampsia and this may influence the interpretation of research data. Others argue that since maternal and fetal outcomes are similar regardless of the specificity of the classification, it is safer to use the inclusive definition. A second controversial issue is the definition of hypertension in pregnancy.

A blood pressure of ≥ 140/90 mmHg has traditionally been used to make the diagnosis. Further studies are required to determine whether this cutoff provides the optimal balance between sensitivity and specificity. On a positive note, until recently, the method of measurement has been debated, but it is now accepted that the Korotkoff V sound should be used to determine diastolic pressure. While the most recent guidelines of the American College of Obstetricians and Gynecologists (ACOG) have excluded any comparison with early-trimester/nonpregnant blood pressure as part of the diagnostic criteria, many investigators still believe that adherence to an absolute blood pressure limit may miss a subgroup of women with preeclampsia. Moreover, this change in the ACOG guidelines may temper some of the conclusions derived from studies that included such women.

As for proteinuria, the diagnosis is far more inaccurate and subjective than that of hypertension. Recent studies confirm that dipstick urinalysis in hypertensive pregnancy is at best a rough screen for the presence or absence of true proteinuria.

The diagnosis and classification of the hypertensive disorders of pregnancy has been reviewed recently (1). This chapter attempts to update some of these issues, including the variability in diagnoses, the detection of proteinuria, and the difficulty of making the distinction between gestational hypertension and preeclampsia.

II. THE EXTENT OF THE PROBLEM

The authors of two recent reviews have analyzed manuscripts relating to preeclampsia published between 1997 and 1998 (2,3). These reviews demonstrated that the various methods for defining hypertension and proteinuria were so diverse that data could rarely be considered comparable. In an analysis of 135 articles from nine major journals, Harlow and Brown (3) found that there were major variations in the terminology and diagnostic criteria. In up to 30% of papers, no adequate definition of preeclampsia was given. When preeclampsia was defined, 80% of the papers required that both hypertension and proteinuria be present, while other papers required evidence of hypertension and multisystem organ dysfunction (e.g., renal, liver, cerebral involvement, thrombocytopenia) or only hypertension and edema. The methods for defining proteinuria varied. Up to one-fifth of papers relied on dipstick urinalysis despite its high false-positive and false-negative rates (discussed below). Seven percent of articles used urinary protein concentration (rather than excretion rate), which may be inaccurate due to the fact that it is influenced by the state of hydration and the urine flow rate. The definition of hypertension was generally around 140/90 mmHg. We noted that in about three-quarters of the papers, the authors included either systolic or diastolic pressure for their diagnosis. Chappell (2) found that about half relied on diastolic pressure alone. In two-thirds of the studies, hypertension was diagnosed on the basis of a single blood pressure reading despite the fact that “white-coat hypertension” has been shown to account for at least 25% of cases of elevated blood pressure in the clinic (4).

The three main variables affecting the accuracy of a blood pressure measurement are the device employed, the Korotkoff sound used to record the diastolic blood pressure, and the size of the blood pressure cuff. These details were not documented at all in 70 to 90% of the articles reviewed. In other words, even though there seems to be reasonable agreement in the literature as to what constitutes hypertension in pregnancy, there is still great variability in the way in which we arrive at such a blood pressure measurement. These two reviews are important in that they agree in their analyses and show that the diversity of definitions and diagnostic criteria for preeclampsia are such that the groups of women reported in these international journals could rarely be considered truly comparable.

III. COMPARISON OF AVAILABLE CLASSIFICATION SYSTEMS

Classifying the hypertensive disorders stimulates opposing opinions. The “inclusive” system is based on a pathophysiological description of preeclampsia as a multisystem disorder (5) and has been adopted by the Australasian Society for the Study of Hypertension in Pregnancy (ASSHP) (6). The “restrictive” classification, adopted by the (USA) National High Blood Pressure Education Program (NHBPEP) (8), limits the criteria of the diagnosis of preeclampsia to that of hypertension and proteinuria and provides differential guidance for clinical and research purposes.

It could be argued that a classification system for hypertension in pregnancy is not necessary. Increased blood pressure, whether associated with proteinuria or not, is a sign that deserves attention. On one hand, artificial classification may falsely reassure the clinician and lead to inadequate investigation and treatment of hypertension. On the other hand, an inclusive and generalized classification may lead to expensive and unnecessary intervention. The majority of care providers still find a classification system useful in order to translate research findings and management guidelines into clinical practice.

A. Requirements of a Good Classification System

The first major requirement of a classification system for hypertension in pregnancy should be the ability to stratify patients according to risk for adverse maternal and perinatal outcome, so that appropriate intervention and management can be instituted. An important discriminator is whether the hypertension arose de novo during the pregnancy or predated it. A system that can differentiate between de novo preeclampsia and underlying chronic hypertension would identify women at higher risk for adverse pregnancy outcomes but lower long-term risk. At a time when outpatient management is becoming popular, the ability to classify patients according to risk has become paramount.

B. Terminology of the Currently Available Systems

Chronic hypertension is perhaps the least debated term in current usage. Within this group, differentiation between women with essential hypertension and those with secondary hypertension is important, particularly since the latter may be reversible. This distinction is clearly made in the ASSHP and the Canadian (8) systems.

De novo hypertension in pregnancy is given a wide range of terms, including preeclampsia and gestational hypertension. The fact that preeclampsia does not include the word hypertension is a distinct advantage, as preeclampsia should be thought of as a multisystem disorder with elevated blood pressure as one component. Gestational hypertension describes high blood pressure pertaining to pregnancy with no other features of preeclampsia. This term seems appropriate, as blood pressure returns to normal after delivery. The inclusion of the word hypertension in this terminology is appropriate, because elevation of blood pressure is the only abnormality. Preeclampsia has been classified as mild or severe in some classification systems (9,10), but the definition of mild preeclampsia is inconsistent. This may lead to confusion between mild preeclampsia and gestational hypertension, and for this reason the latest ASSHP classification does not stratify preeclampsia (6). Gestational hypertension should not be confused with mild preeclampsia, since the two conditions are distinct.

C. Current Classification Systems

The currently used classification systems are summarized in Tables 1 2 3 4. The International Society for the Study of Hypertension in Pregnancy (ISSHP) has a deta...