Hypertension in pregnancy: Definitions, familial factor, and remote prognosis

The literature dealing with the hypertensive disorders of pregnancy is often confusing. One reason for this is the difficulty in distinguishing clinically between the various causes of hypertension in pregnancy, such as essential hypertension, preeclampsia, or hypertension secondary to renal disease. Another problem is that classifications used in the literature are frequently too detailed and cumbersome, and some are erroneous. This review summarizes the current concepts regarding high blood pressure in gestation, with emphasis on a familial factor in preeclampsia. In addition, the remote cardiovascular prognosis of hypertension in pregnancy is discussed. The Committee on Terminology of the American College of Obstetricians and Gynecologists [1] defines gestational hypertension as certain elevations in blood pressure in late pregnancy or the early puerperium, without proteinuria or abnormal edema, and with a fall to normal levels within 10 days after delivery. There are four criteria for the diagnosis of hypertension, any one of which suffices in a pregnant woman: (1) a rise of at least 30mm Hg over the usual level of systolic pressure, (2) a rise of at least 15mm Hg over the usual level of diastolic pressure, (3) a systolic pressure of at least 140mm Hg, and (4) a diastolic pressure of at least 90mm Hg. The abnormal changes or levels must be observed on at least two occasions, at least 6 hours apart. The American Committee on Maternal Welfare [2] had proposed a classification that was used for many years; the diagnosis of preeclampsia could be, and often was, made on the basis of gestational hypertension alone. Nelson's [3] classification, widely used in the British Isles, ignores edema, and the diagnosis of mild preeclampsia is made on the basis of gestational hypertension alone. (If proteinuria of 0.25 g/liter or more appears in addition to hypertension, the diagnosis of severe preeclampsia is made, although it often is not severe or even preeclampsia). Most, but not all, diagnoses of mild preeclampsia have been made on the sole criterion of gestational hypertension, which has several causes other than preeclampsia. In an effort to define preeclampsia more precisely, the Committee on Terminology [1] assigned gestational hypertension to a separate category and specified that the diagnosis of preeclampsia must depend upon hypertension together with significant proteinuria, or edema of the hands or face, or both. Actually, the diagnosis is insecure in the absence of proteinuria. "Significant proteinuria" is defined as at least 0.3 g/liter in a 24-hour collection of urine, or 1 g/liter in a random sample. Eclampsia is convulsions in women with preeclampsia; epilepsy and other convulsive disorders must be excluded. Preeclampsia-eclampsia is peculiar to pregnancy, and it appears with increasing frequency as pregnancy approaches term; it is unusual before the end of the second trimester. Nulliparas are from 6 to 8 times more susceptible to preeclampsia than are multiparas, and when the diagnosis is made in a multipara it usually is erroneous. What is diagnosed as preeclampsia, especially mild preeclampsia, often is not preeclampsia, as is documented elsewhere [4]. It may be: (1) preeclampsia; that is, the diagnosis may be correct in perhaps half of cases; (2) latent hypertension revealed by pregnancy, as will be discussed (3) chronic glomerulonephritis or other renal disease, as proved by renal biopsies [5–7]; and (4) frank essential or renal hypertension that had abated during much of pregnancy, as happens in from 30 to 40% of hypertensive women, often with "normal" levels during midpregnancy [8–11]. Predisposing factors to preeclampsia include nulliparity, familial history of preeclampsia-eclampsia, plural gestation, diabetes, chronic hypertension, a large, rapidly growing hydatidiform mole, fetal hydrops, and extremes of age.