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Thyroid Disease in Pregnancy


A. Mother

1. Increased thyroxine-binding globulin (TBG) levels after 3 weeks (peak 12-14 weeks, plateau to term)

2. Normal thyroid-stimulating hormone (TSH) (but declines slightly as chorionic gonadotropin [hCG] rises), increased responsiveness to thyrotropin-releasing hormone (TRH)

3. Normal T4 production and turnover rates

4. Thyroglobulin (Tg) rises throughout, especially in the last trimester

5. Increased radioactive iodine uptake U) (contraindicated in pregnancy)

a. Increased renal clearance of iodide leads to decreased iodide space

b. Increased thyroidal clearance of iodide leads to normal total iodide uptake

6. Mild thyroid enlargement (goiter) in 15-85 % (different series)

a. Mainly in areas of iodine deficiency; responds to iodine prophylaxis

b. Goiter is seldom seen in North America. If occurs, evaluation warranted

7. Increased basal metabolic rate (BMR): fetus plus increased cardiac output plus respiratory and muscular work

8. Increased cholesterol

B. Fetus

1. Thyroid

2. Hypothalamus-pituitary

C. Placenta