Hypertension unique to pregnancy is best termed pregnancy-induced hypertension (PIH). PIH is synonymous with preeclampsia-eclampsia (eclampsia being an extension of the preeclarmptic process) and replaces the older term toxemia. Although the cause is unknown, there are many theories, none of these hypotheses, however, fully explains the disease entity. It is likely that the cause of PIH will be found to be multifactorial. Socioeconomic factors, nutritional deficiencies, and slow disseminated intravascular coagulation (DIC) have been postulated as etiologic agents, but may actually be only associated factors. Recent immunologic explanations are intriguing but not proven. There is a familial tendeney observed for preeclampsia. In one large follow-up study of eclamptic women, preeclampsia occurred in 27% of the first pregnancies of sisters of eclamptic women. In 14% of the women who had severe PIH, severe preeclampsia

developed in the second pregnancy . Any theory of PIH must explain the following observations: (1) PIH is principally a disease of primigravid women; (2) it is unique to humans; (3) it is associated with a large amount of trophoblasts; (4) there is coordination with chronic vascular disease; (5) there is a genetic predisposition; and (6) a viable fetus is not always present.

In a recent large prospective multicenter study of nulliparous women, only four characteristics predicted the development of preeclampsia (in order of importance): (1) systolic blood pressure at first prenatal visit; (2) obesity; (3) prior abortion or miscarriage; and (4) cigarette smoking. The higher the systolic blood pressure at the first prenatal visit the higher the incidence of preclampsia. Likewise, the more obese the women were at the start of pregnancy, the higher

the incidence of preeclampsia. A prior abortion or miscarriage and cigarette smoking reduce the incidence of preeclampsia. Low-dose aspirin and calcium have both been felt or reduce the incidence of preeclampsia. However, large prospective studies have failed to demonstrate that low-dose aspirin or calcium supplementation prevents preeclampsia.

In terms of the basic physiology involved, hypertension is a consequence of either cardiac output or peripheral vascular resistance. Cardiac output remains normal during pregnancy ; therefore, PIH results from increased peripheral vascular resistance. This vascular resistance is caused by the generalized vasospasm so characteristic of hypertension. Early in normal pregnancy, the mother' s arteries become more refractory to the effects of pressor agents such as angiotensin

II. The cause of this normal increase in vascular refractoriness is not known, but prostaglandins play a role. Many weeks before the onset of clinically detectablc PIH, there is a loss of refractoriness to infused angiotensin. The results of angiotensin infusions can actually predict which normotensive: patients are destined to acquire PIH. After the loss of vascular refrectoriness to angiotensin but before the onset of clinical hypertension, there is a decrease in placental

perfusion (as measured by the clearance of dehydroisoandrosterone sulfate). It is now understood that PIH is a chronic disease process and that hypertension occurs relatively late in its course. By the time elevated blood pressure is detected, the discase is well established.

The diagnosis of PIH is determined by the presence of hypertension in conjunction with proteinuria, edema, or both, after the 20 week of pregnancy. It is primarily a disease of the first pregnancy, and it occurs with higher frequency in younger (adolescent) and older (older than 35) primigravidas. The diagnosis of PIH in the multigravid woman is often incorrect and should be made only after ruling out cardiovascular and renal disease. Hypertension is defined as a blood

pressure reading of greater than 140/90 mm Hg.Two blood pressure readings taken at least 6h apart are required for determining this. Proteinuria is a more important diagnostic criterion than nondependent edema, but both nornally occur later than hypertension. Significant proteinuria is defned as a protein level of 500 mg/dl, or more per 24 hours, which approximates a 2+ urinary protein level. Ederna is such a common ocсurrеnce that it is often not helpful for diagnosis. Nondependent edema is significant, but as many as eight in 10 nornotensive women exhibit dependent edema.

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