Question of the Week # 419

419) A 26-year-old woman presents for an ante-natal check up after her home pregnancy test showed positive result. Her last menstrual period was 5 weeks ago. Her past medical history includes hypothyroidism for which she has been using 125 mcg of levo-thyroxine for the past five years. She did not require any dose adjustment of her thyroid hormone therapy in the past 4 years. Her most recent thyroid stimulating hormone level ( TSH) was performed 2 weeks ago and was 2.5µU/ml ( N = 0.5 to 5.0 µU/ml). She denies any cold intolerance, weakness or constipation. She has gained about 2 lbs weight in the past one month. On physical examination, vitals are stable. There is no goiter. Reflexes are 1+ in bilateral lower extremities and there is 1+ pre-tibial edema. Laboratory investigations reveal :

Thyroid Stimulating Hormone :  2.5 µU/ml( N = 0.5 to 5.0 µU/ml)

Serum Total T4: 13.9 µg/dl ( N = 5 to 12µg/dl)

Serum Free T4 :  1.9 ng/dl ( N = 0.9 to 2.4ng/dl)

Which of the following is the most recommendation?

A) Decrease Levothyroxine and recheck TSH in 4 weeks

B) Continue same dose Levothyroxine and repeat TSH in 4 weeks

C) Increase Levothyroxine and repeat TSH in 4 weeks

D) Repeat TSH in 8 to 10 weeks

E) Check Serum thyroid binding globulin levels

11 Responses

  1. C

  2. E

  3. C. As in pregnancy you need to increase the dosage of peck thyroxine . Thyroid hormone requirements increases in pregnancy , and previously well controlled women can become symptomatic.

  4. e

  5. C) Increase Levothyroxine and repeat TSH in 4 weeks- increased levothyroxine requirement due to increase in thyroxine binding globulin during pregnancy resulting low free T4 (but high Serum Total T4)

  6. b

  7. ans

  8. C.

  9. C-increase Levothyrox due to increase TBG f/u tsh in 4 wks

  10. When a patient with primary hypothyroidism is planning a pregnancy, it seems reasonable to proactively implement a plan to avoid exacerbation of the hypothyroidism. Early in the pregnancy, the fetus is completely depen-dent on maternal triiodothyronine and thyroxine. Further, the pharmacodynamic effect of levothyroxine does not manifest until the patient has been taking it for 4–6 weeks. As such, the practical solution offered by Alexander and colleagues seems reasonable:2 upon confirmation of pregnancy, the current dose of levothyroxine should be increased by 29%, or the equivalent of 2 additional doses per week. They suggest that this dose be continued until thyroid function testing is performed. It is prudent that health care providers inform patients of the potential interaction between perinatal vitamins and levothyroxine to avoid any potential reduction in levothyroxine efficacy.

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