A 32-year-old woman, gravida 1 para 0, calls the office to schedule her first prenatal visit. Her last menstrual period was 5 weeks ago and she had a positive pregnancy test 2 days ago. The patient feels well and has no vaginal bleeding or cramping. She was diagnosed with Hashimoto thyroiditis 4 years ago and has been on a stable dose of levothyroxine for the past 2 years. Serum TSH 3 months ago was within normal limits. The patient has no other chronic medical conditions or previous surgeries. She has started taking a prenatal vitamin daily. Family history is significant for a sister currently undergoing evaluation for recurrent miscarriages. The patient does not use tobacco, alcohol, or illicit drugs. She is nervous about her sister's obstetric history and asks if she needs to make any changes to her medication. Which of the following would be the most appropriate response to this patient?

Question

A 32-year-old woman, gravida 1 para 0, calls the office to schedule her first prenatal visit.  Her last menstrual period was 5 weeks ago and she had a positive pregnancy test 2 days ago.  The patient feels well and has no vaginal bleeding or cramping.  She was diagnosed with Hashimoto thyroiditis 4 years ago and has been on a stable dose of levothyroxine for the past 2 years.  Serum TSH 3 months ago was within normal limits.  The patient has no other chronic medical conditions or previous surgeries.  She has started taking a prenatal vitamin daily.  Family history is significant for a sister currently undergoing evaluation for recurrent miscarriages.  The patient does not use tobacco, alcohol, or illicit drugs.  She is nervous about her sister's obstetric history and asks if she needs to make any changes to her medication.  Which of the following would be the most appropriate response to this patient?

Quizplus · Accepted Answer

Explanation: 11ec2b69_becd_7966_8f63_edea8fb518ec_MD0005_00 Thyroid physiology changes during pregnancy to meet increased metabolic demands. During the first trimester, β-hCG binds TSH receptors on thyroid follicular cells and stimulates thyroid hormone production. The resulting elevations in T3 and T4 suppress TSH secretion. Concurrently, elevated estrogen levels cause an increase in serum thyroxine-binding globulin (TBG), which leads to higher total T3 and T4 levels. Thyroid hormone requirements increase by about 25%-50% over the prepregnancy state. Patients with normal thyroid function can increase thyroid hormone production to saturate the elevated number of thyroid hormone binding sites on TBG, but patients with primary hypothyroidism are unable to increase thyroid hormone production. In light of this, current guidelines advise that the dose of levothyroxine be empirically increased by approximately 30% (eg, 2 additional levothyroxine doses weekly) at the time the pregnancy is first detected (Choices B and E). Subsequently, TSH should be measured every 4 weeks and the dose adjusted to maintain TSH within trimester-specific norms. (Choice A) T3 is made primarily in the peripheral tissues, and circulating levels correlate poorly with thyroid status in hypothyroidism. If assessment of thyroid hormone is needed during pregnancy, free T4 (using trimester-specific norms) or total T4 can be measured. However, the dose of levothyroxine should be increased first, and TSH is usually adequate for monitoring of thyroid status. (Choice C) Levothyroxine replacement should not be discontinued during early pregnancy. The fetus is completely dependent on maternal thyroid hormone for brain development until 12 weeks gestation when the fetal thyroid gland is fully developed. Educational objective: Newly pregnant patients with hypothyroidism should increase their levothyroxine dose at the time pregnancy is detected. TSH is then checked every 4 weeks with the levothyroxine dose adjusted to trimester-specific norms. References: Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. (http://www.ncbi.nlm.nih.gov/pubmed/22954017) Thyroid dysfunction during pregnancy and in postpartum period: treatment and latest recommendations. (http://www.ncbi.nlm.nih.gov/pubmed/24510157)

A 32-Year-Old Woman, Gravida 1 Para 0, Calls the Office