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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Hypertension in Pregnancy
Sponsored by The Indian Health Service Clinical Support Center
Part 2: Severe Pre-Eclampsia
3. Read the background material.
Background
Hypertensive disease complicates 6-22% of all pregnancies, depending on the population studied, and is the third leading cause of maternal death worldwide. It accounts for 18% of maternal deaths in the United States and, because it prompts the need for preterm delivery, is a significant cause of perinatal mortality as well. Every provider caring for pregnant women needs to be familiar with the unique aspects of this disorder, and understand that this is not necessarily the same entity familiar to them in the non-pregnant population.
Native Americans
Hypertension has been reported less frequently among American Indians compared to other U.S. groups, but is increasing in frequency, is strongly associated with obesity and diabetes, and is synergistically associated with diabetes in the etiology of end-stage renal disease. The first priority for dealing with hypertension among American Indians is to maximize efforts toward control. The Indian Health Service (IHS) and the tribes provide such an opportunity, which is not as readily available to other minorities.
A retrospective chart review of all pregnancies in 1991 at the Crownpoint Indian Health Service facility in Crownpoint revealed hypertensive disorders in 12.6% among the Navajo. The Navajos are the largest Native American tribe. They, like other Native Americans, appear to be in an "epidemiologic transition" and are accordingly experiencing increased rates of hypertension, diabetes, and obesity. Similar changes have been documented outside of pregnancy with Indian and Alaska Natives.
Definitions
The National High Blood Pressure Education Program Working Group on High Blood Pressure in Pregnancy recently published new evidence-based guidelines on the classification, pathophysiology, and management of this disorder. This classification defines and stratifies the hypertensive disorders into four categories:
- Chronic hypertension
- Preeclampsia-eclampsia
- Preeclampsia superimposed on chronic hypertension
- Gestational hypertension
Chronic hypertension is defined as hypertension that was present prior to pregnancy or diagnosed prior to 20 weeks gestation. Hypertension is defined as blood pressure (BP) >140 mm Hg systolic or >90 mm Hg diastolic.
Preeclampsia-eclampsia is defined as gestational blood pressure elevation accompanied by proteinuria. This entity can be diagnosed after 20 weeks gestation in a woman with the same >140/90 BP criteria who also has >1+ proteinuria (>30 mg/dL) on dipstick, or >0.3 g on a 24 hour urine collection.
Preeclampsia superimposed on chronic hypertension is diagnosed in the woman with known non-proteinuric hypertension at <20 weeks who develops new onset proteinuria as defined above.
Gestational hypertension is an interesting entity diagnosed by blood pressure elevation after mid-pregnancy without proteinuria.
This classification system has important clinical management implications that will be discussed in detail below. In general, preeclampsia should always be suspected, since it has the worst maternal and perinatal outcomes and, at the present time, can only be cured by delivery. The long-term outcome of women with each of these disorders is also different, and may have significant future long term public health implications as well.
Key details relevant to this classification system
Accurate, precise and consistent blood pressure measurement
The only objective physical findings measured that affects the diagnosis of hypertension in pregnancy is the blood pressure reading. Diastolic blood pressure is defined as the disappearance of sound (Korotkoff phase V), not muffling of sound. Blood pressure should be measured with the patient in the sitting position and confirmed by repeating after a period of rest. The pressure will almost always decrease with the patient in lateral decubitus position, and while this is the therapeutic position, it will falsify the diagnosis. It was previously recommended that an increment of 30 mm Hg systolic or 15 mm Hg diastolic BP from first trimester reading should be used as a diagnostic criterion, but the evidence does not support that such women will have adverse outcomes and is no longer used.
Other physical findings
Edema has also been eliminated as a diagnostic criterion for preeclampsia, as most normal women in late pregnancy will have it to some degree, thus making it of limited discriminant value. Nevertheless, rapid short-term weight gain may be an important first clue that the syndrome is about to manifest itself.
Urine protein measurement
The standard urine dipstick test has neither adequate sensitivity, nor specificity. The standard urine dipstick should not be used as a screening test in the general prenatal population. Proteinuria should not be diagnosed in a woman with a current urinary tract infection.
On the other hand, if the patient has an elevated blood pressure or symptoms of pre-eclampsia, then a random spot urine collection, corrected for creatinine excretion, the protein/creatinine ratio, has a correlation coefficient of .90 with the 24-hour collection, is user-friendly, and expeditious. Values >0.20 have comparable diagnostic value for preeclampsia as 24-hour collections with >300 mg.
24-hour urine collections are more accurate than dipstick protein determinations, but are cumbersome, time-consuming, and do not always represent complete collections.
Other laboratory markers
Besides proteinuria, there are no laboratory markers of preeclampsia. Some laboratory studies may be of key importance as ancillary guides to management (see below), but they cannot be used to make the actual clinical diagnosis. In particular, the diagnostic value of uric acid determinations, while classic teaching, has neither specificity, nor sensitivity, or prognostic value for this disease.
Summary: The role of screening
Screening for preeclampsia with blood pressure measurement is recommended for all pregnant women at the first prenatal visit and periodically throughout the remainder of pregnancy.
The optimal frequency for measuring blood pressure in pregnant women has not been determined and is left to clinical discretion it is most efficient to measure blood pressure on women who are being seen by their clinicians for other reasons. The collection of meaningful blood pressure data requires consistent use of correct technique and a cuff of appropriate size. The patient should be in the sitting position and the blood pressure should be measured after the patient's arm has rested at heart level for 5 minutes.
N.B.
Further diagnostic evaluation and clinical monitoring, including frequent blood pressure monitoring and urine testing for protein, are indicated only if blood pressure does not decrease normally during the middle trimester, or if the blood pressure exceeds 140/90 mm Hg. (U.S.P.S.T.F.)\. There is no role for urine screening the general prenatal population for dipstick proteinuria.
