In a 24-year-old primigravida at 11 weeks gestation presenting with lethargy, constipation, cold intolerance and elevated thyroid‑stimulating hormone, what is the most appropriate management?

Management of Hypothyroidism in Early Pregnancy

Initiate levothyroxine (thyroxin) immediately to prevent adverse pregnancy outcomes and potential neurodevelopmental harm to the fetus. 1, 2, 3

Rationale for Immediate Treatment

• Maternal hypothyroidism at 11 weeks gestation poses significant risks including preeclampsia, preterm delivery, low birth weight, and critically—potential permanent neurodevelopmental deficits in the child 1, 3, 4

• Fetal brain development is critically dependent on maternal thyroid hormone during the first and second trimesters, as the fetal thyroid does not produce adequate hormone until mid-gestation 3, 4

• Untreated or inadequately treated maternal hypothyroidism is associated with impaired cognitive development in offspring, making prompt treatment essential 1, 4

Treatment Protocol

Initial Dosing

• For new-onset hypothyroidism with TSH ≥10 mIU/L in pregnancy, start levothyroxine at 1.6 mcg/kg/day 2

• If TSH <10 mIU/L, initiate at 1.0 mcg/kg/day 2

• Levothyroxine monotherapy is the only appropriate treatment during pregnancy—T3 supplementation provides inadequate fetal thyroid hormone delivery 1

Monitoring Schedule

• Check TSH and free T4 every 4 weeks until stable, then at minimum once per trimester 2, 3

• Target TSH <2.5 mIU/L in the first trimester using trimester-specific reference ranges 2, 3

• More than 50% of pregnant women with hypothyroidism require dose increases during pregnancy, typically by 25-50% above pre-pregnancy levels 3

Critical Safety Considerations

• Before initiating levothyroxine, rule out concurrent adrenal insufficiency by checking morning cortisol and ACTH, as starting thyroid hormone before adequate corticosteroid coverage can precipitate life-threatening adrenal crisis 1

• Take levothyroxine on an empty stomach, 30-60 minutes before breakfast, at least 4 hours apart from iron, calcium supplements, or antacids for optimal absorption 1

Why Other Options Are Incorrect

• Propylthiouracil (Option A) is an antithyroid medication used for hyperthyroidism (Graves' disease), not hypothyroidism—this would worsen the patient's condition 5

• Multivitamins (Option B) do not address thyroid hormone deficiency and will not prevent the serious maternal and fetal complications of untreated hypothyroidism 1

• Thyroidectomy (Option D) would eliminate remaining thyroid function and is contraindicated in hypothyroidism—this is a treatment for hyperthyroidism or thyroid cancer 1

Addressing Maternal Concerns About Intellectual Disability

• Prompt initiation of levothyroxine with appropriate monitoring significantly reduces the risk of neurodevelopmental impairment in the offspring 3, 4

• The risk of intellectual disability is primarily associated with untreated or inadequately treated maternal hypothyroidism, not with appropriate levothyroxine therapy 1, 4

• Levothyroxine is safe for lifelong use when properly dosed and monitored—the primary risks result from undertreatment or overtreatment, not from the medication itself at replacement doses 1

Common Pitfalls to Avoid

• Never delay treatment waiting for repeat testing in pregnant women—fetal harm can occur before maternal symptoms fully manifest 1

• Do not use standard non-pregnancy TSH reference ranges—pregnancy-specific targets are lower (TSH <2.5 mIU/L in first trimester) 2, 3

• Avoid undertreating by failing to increase the dose during pregnancy—levothyroxine requirements typically increase by 25-50% and should be adjusted proactively 2, 3

• Never discontinue levothyroxine during pregnancy, as this increases risk of preeclampsia, gestational hypertension, stillbirth, and premature delivery 1