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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Hypertension in Pregnancy
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Part 3: Gestational Hypertension and Chronic Hypertension in Pregnancy
4. Read the material on chronic hypertension in pregnancy
Women who enter pregnancy with high blood pressure are obviously different from those who later develop the preeclampsia syndrome. Nevertheless, their underlying disease may complicate their pregnancy, and up to one in three of them will develop superimposed preeclampsia. Likewise, a third of them may have a small for gestational age infant, and they are at increased risk for preterm birth, placental abruption, and perinatal death. If significant renal disease is part of their picture (creatinine >1.4 mg/dL), these risks will all be exaggerated.
Physiology
The normal physiology of pregnancy may be expected to lower blood pressure in most of these women. As noted above, pregnancy's physiology is geared to enhancing cardiac output to meet the needs of the fetoplacental unit, and a reduction of systemic vascular resistance (afterload) is a sentinel event beginning in early gestation. (See also: Part 1 - mild pre-eclampsia physiology, and Part 2 - severe pre-eclampsia physiology.)
Management
Women with chronic hypertension should be evaluated for potentially reversible etiologies, preferably prior to pregnancy. Women with long-standing hypertension should be evaluated for end-organ disease, including cardiomegaly, renal insufficiency, and retinopathy, preferably prior to pregnancy.
Effect of chronic antihypertensive medications
Most women with mild blood pressure elevation who are already on anti-hypertensive medications can usually stop them in early gestation without ill effect. There is no evidence that anti-hypertensive therapy will improve perinatal outcome, and most studies show an increase in fetal growth restriction in women on such medications. This is especially true for the beta-blockers, with the exception of labetalol.
Methyldopa and hydralazine have the best "track records" and are the preferred agents. ACE inhibitors have been implicated in causing fetal renal failure (after the first trimester) and are contraindicated. There is little data on calcium channel blockers, but what does exist shows neither deleterious nor advantageous effects from their use. Diuretics are not contraindicated, but the aforementioned physiology of pregnancy with respect to volume expansion would seem to militate against them having much effect. The goal is to maintain perfusion and keep the diastolic pressure in the 90-100 mm Hg range. At this point there is not consistent evidence to demonstrate that bed rest is an effective therapy.
Baseline studies
Appropriate baseline studies in women with chronic hypertension include an evaluation of preexisting target organ damage. Renal function can be assessed with a 24-hour urine protein and creatinine excretion, and/or a serum creatinine and a spot urine protein/creatinine ratio. If secondary hypertension is suspected, a renal ultrasound may have a small yield. Ophthalmoscopy can determine if any preexisting retinopathy is present. An EKG to look for the presence of left ventricular hypertrophy would be informative in order to anticipate the possible emergence of diastolic dysfunction later in the pregnancy. A baseline ultrasound for dating the pregnancy is important, and follow-up scans, beginning at 28 weeks and continuing monthly until term, should be obtained to look for fetal growth restriction.
Antenatal fetal surveillance
Weekly non-stress testing after 32 weeks may be prudent, but there is little objective evidence of its benefit. If fetal growth restriction, oligohydramnios, or superimposed preeclampsia is diagnosed however, twice weekly NST should be instituted at that time. The uncomplicated patient can be delivered at term, but if the above problems are diagnosed, timing of delivery will depend on their severity.
Superimposed pre-eclampsia
The management of superimposed pre-eclampsia is the same as detailed in Management: Mild Pre-elampsia and Management: Severe Pre-eclampsia. Remember that preexisting renal or cardiac damage may significantly complicate the course and management of severe preeclampsia in these women.
