Chapter 007. Medical Disorders during Pregnancy (Part 6)

Thyroid Disease (See also Chap. 335) In pregnancy, the estrogen-induced increase in thyroxine-binding globulin causes an increase in circulating levels of total T 3 and total T4. The normal range of circulating levels of free T4, free T3, and thyroidstimulating hormone (TSH) remain unaltered by pregnancy.The thyroid gland normally enlarges during pregnancy. Maternal hyperthyroidism occurs at a rate of ~2 per 1000 pregnancies and is generally well tolerated by pregnant women. Clinical signs and symptoms should alert the physician to the occurrence of this disease. Many of the physiologic adaptations to pregnancy may mimic subtle signs of hyperthyroidism. Although...
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Chapter 007. Medical Disorders during Pregnancy (Part 6) Chapter 007. Medical Disorders during Pregnancy (Part 6) Thyroid Disease (See also Chap. 335) In pregnancy, the estrogen-induced increase inthyroxine-binding globulin causes an increase in circulating levels of total T 3 andtotal T4. The normal range of circulating levels of free T4, free T3, and thyroid-stimulating hormone (TSH) remain unaltered by pregnancy. The thyroid gland normally enlarges during pregnancy. Maternalhyperthyroidism occurs at a rate of ~2 per 1000 pregnancies and is generally welltolerated by pregnant women. Clinical signs and symptoms should alert thephysician to the occurrence of this disease. Many of the physiologic adaptations topregnancy may mimic subtle signs of hyperthyroidism. Although pregnant womenare able to tolerate mild hyperthyroidism without adverse sequelae, more severehyperthyroidism can cause spontaneous abortion or premature labor, and thyroidstorm is associated with a significant risk of maternal mortality. Hyperthyroidism in Pregnancy: Treatment Hyperthyroidism in pregnancy should be aggressively evaluated andtreated. The treatment of choice is propylthiouracil. Because it crosses theplacenta, the minimum effective dose should be used to maintain free T 4 in theupper normal range. Methimazole crosses the placenta to a greater degree thanpropylthiouracil and has been associated with fetal aplasia cutis. Radioiodineshould not be used during pregnancy, either for scanning or treatment, because ofeffects on the fetal thyroid. In emergent circumstances, additional treatment withbeta blockers and a saturated solution of potassium iodide may be necessary.Hyperthyroidism is most difficult to control in the first trimester of pregnancy andeasiest to control in the third trimester. The goal of therapy for hypothyroidism is to maintain the serum TSH in thenormal range, and thyroxine is the drug of choice. Children born to women withan elevated serum TSH (and a normal total thyroxine) during pregnancy haveimpaired performance on neuropsychologic tests. During pregnancy, the dose ofthyroxine required to keep the TSH in the normal range rises. In one study, themean replacement dose of thyroxine required to maintain the TSH in the normalrange was 0.1 mg daily before pregnancy, and it increased to 0.15 mg daily duringpregnancy. Since the increased thyroxine requirement occurs as early as the fifthweek of pregnancy, one approach is to increase the thyroxine dose by 30% as soonas pregnancy is diagnosed and then adjust the dose by serial measurement of TSH. Hematologic Disorders Pregnancy has been described as a state of physiologic anemia. Part of thereduction in hemoglobin concentration is dilutional, but iron and folatedeficiencies are the major causes of correctable anemia during pregnancy. In populations at high risk for hemoglobinopathies (Chap. 99), hemoglobinelectrophoresis should be performed as part of the prenatal screen.Hemoglobinopathies can be associated with increased maternal and fetalmorbidity and mortality. Management is tailored to the specific hemoglobinopathyand is generally the same for both pregnant and nonpregnant women. Prenataldiagnosis of hemoglobinopathies in the fetus is readily available and should bediscussed with prospective parents either prior to or early in pregnancy. Thrombocytopenia occurs commonly during pregnancy. The majority ofcases are benign gestational thrombocytopenias, but the differential diagnosisshould include immune thrombocytopenia (Chap. 109) and preeclampsia.Maternal thrombocytopenia may also be caused by catastrophic obstetric eventssuch as retention of a dead fetus, sepsis, abruptio placenta, and amniotic fluidembolism. Neurologic Disorders Headache appearing during pregnancy is usually due to migraine (Chap.15), a condition that may worsen, improve, or be unaffected by pregnancy. A newor worsening headache, particularly if associated with visual blurring, may signaleclampsia (above) or pseudotumor cerebri (benign intracranial hypertension;Chap. 29); diplopia due to a sixth nerve palsy suggests pseudotumor cerebri. Therisk of seizures in patients with epilepsy increases in the postpartum period but notconsistently during pregnancy; management is discussed in Chap. 363. The risk ofstroke is generally thought to increase during pregnancy because of ahypercoagulable state; however, studies suggest that the period of risk occursprimarily in the postpartum period and that both ischemic and hemorrhagic strokesmay occur at this time. Guidelines for use of heparin therapy are summarizedabove (see Deep Venous Thrombosis and Pulmonary Embolism); warfarin isteratogenic and should be avoided. The onset of a new movement disorder during pregnancy suggests choreagravidarum, a variant of Sydenhams chorea associated with rheumatic fever andstreptococcal infection (Chap. 315); the chorea may recur with subsequentpregnancies. Patients with preexisting multiple sclerosis (Chap. 375) experience agradual decrease in the risk of relapses as pregnancy progresses and, conversely,an increase in attack risk during the postpartum period. Beta interferons should notbe administered to pregnant MS patients, but moderate or severe relapses can besafely treated with pulse glucocorticoid therapy. Finally, certain tumors,particularly pituitary adenoma and meningioma (Chap. 374), may manifest duringpregnancy because of accelerated growth, possibly driven by hormonal factors. Peripheral nerve disorders associated with pregnancy include Bells palsy(idiopathic facial paralysis, Chap. 379), which is approximately threefold mo ...