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Teachable Moment
Less Is More
July 2015

Subclinical Hypothyroidism During Pregnancy—Should You Expect This When You Are Expecting?A Teachable Moment

Author Affiliations
  • 1Division of Endocrinology, Diabetes, Metabolism, and Nutrition, Mayo Clinic, Rochester, Minnesota
  • 2Knowledge and Evaluation Research Unit, Mayo Clinic, Rochester, Minnesota
JAMA Intern Med. 2015;175(7):1088-1089. doi:10.1001/jamainternmed.2015.1348

A healthy woman in her 20s was excited to be pregnant with her first child. Eight weeks into her pregnancy, she had her first visit with the obstetrician. She felt well but a bit fatigued. While both of them thought this was rather to be expected, her physician ordered thyroid function tests to rule out hypothyroidism, following case detection guidelines.1,2 The results were soon available at her patient portal. The patient felt reassured to see that all looked normal; the thyroid-stimulating hormone (TSH) level was 2.8 mIU/L (reference range, 0.3-5.0 mIU/L), the free thyroxine (FT4) level was 1.5 ng/dL (reference range, 0.8-1.8 ng/dL), and thyroid peroxidase (TPO) antibodies were undetectable (to convert FT4 to picomoles per liter, multiply by 12.871). A phone call the next day offered unexpected news. To the obstetrician, these findings signaled a thyroid dysfunction. He explained that this abnormality (TSH level >2.5 mIU/L) could cause adverse pregnancy and neonatal outcomes and recommended that she immediately start taking thyroid hormone replacement therapy with levothyroxine, 50 µg, a recommended dose.1 The patient was confused. She thought her results were normal. She wanted a normal pregnancy, however, and followed her physician’s instructions in fear that her unborn child was in danger. Tirelessly, she woke up every day 1 hour earlier to take the medication on an empty stomach and apart from her prenatal vitamins to ensure adequate absorption. Within 2 weeks, she started experiencing palpitations. A severe episode sent her seeking emergency care. After waiting anxiously for hours, she learned her thyroid medicine had caused the tachycardia and that her dose should be reduced. After that, she had monthly thyroid function tests and regular obstetrician visits. She delivered a healthy newborn girl in the hospital, and her pregnancy had no other complications.

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