61: High-Risk Obstetrics

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CHAPTER 61 High-Risk Obstetrics

Brenda A. Bucklin, MD

1 What is a high-risk pregnancy?

High-risk pregnancies include but are not limited to women with:

image Medical complications (e.g., preeclampsia, diabetes mellitus)
image Fetal complications (e.g., prematurity, intrauterine growth restriction, multiple gestations)
image Intrapartum complications (e.g., maternal fever, abnormal vaginal bleeding)

2 Describe the hypertensive disorders of pregnancy

Hypertensive disorders occur in approximately 5% to 10% of all pregnancies. Preeclampsia, chronic hypertension, preeclampsia superimposed on chronic hypertension, and gestational hypertension are terms used to describe the hypertensive disorders of pregnancy. The term pregnancy-induced hypertension (PIH) is no longer used (Table 61-1).

TABLE 61-1 Hypertensive Disorders of Pregnancy*

image

3 What causes preeclampsia?

Preeclampsia is a disorder of unknown etiology. It is a systemic disorder with heterogeneous causes that are linked to maternal, paternal, fetal, and placental factors. In the first stage of the disease process abnormal placentation occurs in which the spiral arteries fail to dilate with or without atherosis. This results in reduced placental perfusion and release of vasoactive substances.

4 What clinical findings are present in preeclampsia?

The principal features of preeclampsia include hypertension and proteinuria. Edema can be physiologic or pathologic and should not be used in the diagnosis of preeclampsia (see Table 61-1).

5 What conditions contribute to maternal and perinatal mortality in preeclampsia?

Complications result from cerebrovascular hemorrhage, stroke, renal or hepatic failures, liver hemorrhage, disseminated intravascular coagulation, abruptio placentae, and pulmonary edema. These complications occur more frequently in women who develop preeclampsia before 32 weeks’ gestation and in those with preexisting medical comorbidities. Perinatal mortality most often results from prematurity.

6 What is HELLP syndrome?

HELLP syndrome (hemolysis, elevated liver enzymes, and low platelet count) is a complication of preeclampsia. Patients develop a microangiopathic hemolytic anemia associated with thrombocytopenia and elevated liver enzymes. Ten to twenty percent of these patients will have normal blood pressure, making the diagnosis sometimes difficult. Although HELLP syndrome is not an indication itself for immediate cesarean delivery, delivery is the only definite treatment for preeclampsia. Patients who develop laboratory evidence of disseminated intravascular coagulation are delivered immediately, regardless of gestational age.

7 How is preeclampsia managed?

Magnesium sulfate is the drug of choice for seizure prophylaxis. Although magnesium has no substantial effect on blood pressure after a bolus dose and the mechanism for the anticonvulsant activity of magnesium is unknown, it attenuates the vascular responses to endogenous and exogenous pressor substances. It also dilates the vascular beds. Other anticonvulsants (e.g., phenytoin, diazepam) have been evaluated, but magnesium sulfate therapy is more effective in preventing recurrent seizures than either phenytoin or diazepam. The benefit of magnesium sulfate administration in women with mild disease is unclear. However, women with severe disease should received magnesium sulfate prophylaxis during labor and after delivery. Acute severe hypertension should be treated to prevent cerebrovascular and cardiovascular complications. Blood pressures should not be normalized. However, blood pressures of at least 160/105 mm Hg should be treated with antihypertensive medications. Because uteroplacental perfusion is proportionate to blood pressure, precipitous decreases in blood pressure can cause fetal compromise.

Antihypertensive agents should be titrated. Although hydralazine is the most commonly administered agent, it was recently compared to intravenous labetalol or oral nifedipine in a metaanalysis of trials. In the systematic review labetalol or nifedipine therapies were as effective as hydralazine in controlling blood pressure with fewer side effects. Labetalol is representative of a class of drugs that act as competitive antagonists at both α- and β-adrenergic receptors. Although systemic vascular resistance is reduced, cardiac output is maintained. Labetalol has also been shown to preserve uteroplacental perfusion. Hydralazine, an arteriolar vasodilator, remains a popular drug for patients with preeclampsia because it increases renal and uterine artery blood flow. The onset and duration are often unpredictable. Side effects include reflex tachycardia and ventricular dysrhythmias. Nifedipine is a calcium channel blocker that prevents the release of calcium, resulting in smooth muscle relaxation. Sodium nitroprusside is another alternative antihypertensive most often administered to patients with refractory hypertension and severe hypertension. Sodium nitroprusside administration requires placement of an arterial catheter to facilitate continuous assessment of maternal blood pressure. Advantages include a fast onset and short duration. It also preserves uteroplacental perfusion. Side effects include reflex tachycardia, cerebral vasodilation, and potential cyanide toxicity.

8 What are the indications for invasive monitoring?

In severe preeclampsia there is no proven benefit of invasive hemodynamic monitoring. Although the indications for invasive central monitoring remain controversial, most agree that the accepted indications include:

image Refractory hypertension.
image Pulmonary edema.
image Refractory oliguria unresponsive to fluid challenge.
image Severe cardiopulmonary disease (Table 61-2).

TABLE 61-2 Indications for Invasive Monitoring in Preeclampsia

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