Treatment of Hyperthyroidism in First Trimester Pregnancy
The most appropriate treatment is B. Propylthiouracil (PTU), which should be initiated immediately as the preferred antithyroid medication during the first trimester of pregnancy. 1, 2
Rationale for PTU as First-Line Therapy
This 9-week pregnant woman presents with clear symptomatic hyperthyroidism (likely Graves' disease based on diffuse goiter with bruit, suppressed TSH <0.01, elevated free T3 and T4, and classic symptoms). PTU is specifically recommended as the preferred antithyroid medication during the first trimester because methimazole is associated with a specific pattern of rare congenital malformations including choanal atresia, aplasia cutis congenita, and facial/gastrointestinal/cardiac anomalies. 3, 1, 2, 4
- The American College of Obstetricians and Gynecologists and American Academy of Family Physicians both recommend PTU exclusively during the first trimester, then switching to methimazole for the second and third trimesters to minimize both congenital malformations and maternal hepatotoxicity 2
- While PTU carries a small risk of hepatotoxicity, this risk is outweighed by the teratogenic concerns with methimazole during organogenesis 3, 2, 5
Why Other Options Are Inappropriate
Option A (Observation) is contraindicated because untreated hyperthyroidism significantly increases maternal and fetal risks:
- Maternal complications include severe preeclampsia, preterm delivery, heart failure, and miscarriage 1, 2
- Fetal complications include stillbirth, low birth weight, and neonatal thyroid dysfunction 1, 5, 6
Option C (Radioactive iodine) is absolutely contraindicated during pregnancy as it causes fetal thyroid ablation 1, 2
Option D (Thyroidectomy) is reserved only for exceptional circumstances:
- Women who do not respond to thioamide therapy 1, 2
- Severe drug intolerance such as agranulocytosis or severe hepatotoxicity 2
- If surgery becomes necessary, the second trimester is the preferred timing 2
Treatment Goals and Monitoring
The goal is to maintain free T4 in the high-normal range using the lowest possible PTU dosage to prevent fetal hypothyroidism and goiter while controlling maternal hyperthyroidism. 1, 2
Specific monitoring protocol:
- Check free T4 or free thyroxine index every 2-4 weeks to adjust medication dosage 1, 2
- Once stable, check TSH every trimester 2
- Monitor for agranulocytosis (sore throat, fever) - if these symptoms develop, obtain complete blood count immediately and discontinue PTU 2, 5
- Monitor fetal heart rate and growth throughout pregnancy 2
Adjunctive therapy:
- Beta-blockers (e.g., propranolol) can temporarily manage symptoms like tremors and palpitations until PTU reduces thyroid hormone levels 1, 2
- Avoid atenolol specifically as it is associated with lower birth weight 3
Critical Management Plan
Plan to switch from PTU to methimazole after the first trimester (around 12-13 weeks) to minimize the risk of maternal hepatotoxicity while avoiding methimazole's teratogenic effects during organogenesis. 2, 4
Important counseling points:
- Inform the patient about the rare risk of PTU-associated hepatotoxicity and instruct her to report tiredness, nausea, anorexia, fever, or malaise immediately 5
- Advise that fetal/neonatal thyroid function will need to be monitored, as PTU crosses the placenta and can cause fetal hypothyroidism with or without goiter in approximately 9.5% of cases 7
- Inform the newborn's physician about maternal Graves' disease due to risk of neonatal thyroid dysfunction 1, 2
- Reassure that breastfeeding is safe with PTU treatment 2