How to manage a female patient with a history of hypothyroidism, currently on levothyroxine (thyroid hormone replacement medication) 125 micrograms, who is planning to get pregnant, with a Thyroid-Stimulating Hormone (TSH) level near the upper limit of normal and a Thyroxine (T4) level close to the lower limit?

Management of Hypothyroidism in a Woman Planning Pregnancy

Direct Recommendation

Increase the levothyroxine dose immediately (Answer A) - this patient's TSH of 4.4 mIU/L is too high for someone planning pregnancy, and her T4 at the lower limit indicates inadequate replacement that will become problematic once she conceives 1, 2.

Rationale for Dose Increase

Pre-pregnancy TSH optimization is critical:

• Women planning pregnancy should have TSH <2.5 mIU/L, ideally <1.2 mIU/L, before conception 1, 3
• When pre-pregnancy TSH is 1.2-2.4 mIU/L, 50% of women require dose increases during pregnancy; when TSH is <1.2 mIU/L, only 17.2% need increases 3
• This patient's TSH of 4.4 mIU/L is nearly double the recommended pre-pregnancy target 1, 2

Pregnancy dramatically increases levothyroxine requirements:

• Thyroid hormone requirements increase 20-47% during pregnancy, with increases beginning as early as week 5 of gestation 4, 5
• The median onset of increased requirements is week 8, plateauing by week 16 5
• Women with pre-existing hypothyroidism should increase levothyroxine by approximately 30% as soon as pregnancy is confirmed 5

Consequences of inadequate treatment:

• Untreated or undertreated hypothyroidism during pregnancy causes preeclampsia, low birth weight, miscarriage, and impaired fetal neurodevelopmental outcomes 1, 2, 6
• Maternal hypothyroxinemia (low T4 with normal TSH) is associated with alterations in fetal neuropsychological development and increased risk of fetal loss 2

Specific Dosing Strategy

Immediate dose adjustment:

• Increase levothyroxine by 12.5-25 mcg based on current dose of 125 mcg 1, 7
• A 25 mcg increase (to 150 mcg daily) would be appropriate given her TSH is significantly elevated and T4 is at the lower limit 1

Monitoring plan:

• Recheck TSH and free T4 in 6-8 weeks after dose adjustment 1, 7
• Target TSH <2.5 mIU/L before attempting conception 1, 2
• Once pregnant, monitor TSH every 4 weeks through midgestation, then at 30 weeks 2, 4

Why Other Options Are Incorrect

Continuing the same dose (Answer C) is inappropriate:

• Her current TSH of 4.4 mIU/L indicates inadequate replacement even for non-pregnant state 1
• This TSH level is far above the recommended pre-pregnancy target of <2.5 mIU/L 1, 2
• Waiting until pregnancy occurs to adjust the dose risks early fetal exposure to maternal hypothyroidism during critical neurodevelopmental windows 6, 5

Decreasing the dose (Answer B) would be harmful:

• There is no indication for dose reduction when TSH is elevated and T4 is at the lower limit 1
• Dose reduction is only indicated when TSH is suppressed (<0.1-0.45 mIU/L) 1

Discontinuing medication (Answer D) is contraindicated:

• This patient has established hypothyroidism requiring lifelong treatment 1
• Discontinuation would lead to overt hypothyroidism with severe maternal and fetal consequences 2, 6

Critical Pitfalls to Avoid

Do not wait until pregnancy is confirmed to optimize thyroid function:

• By the time pregnancy is confirmed (typically 4-5 weeks gestation), fetal thyroid hormone requirements have already begun 5
• Levothyroxine requirements increase as early as week 5 of gestation 5

Do not rely on "normal" TSH ranges for pregnancy planning:

• The upper limit of normal TSH (5.0 mIU/L) is too high for women planning pregnancy 1, 2
• Pre-pregnancy TSH should be optimized to <2.5 mIU/L, ideally <1.2 mIU/L 1, 3

Do not underestimate the magnitude of dose increase needed:

• Most women require 20-47% increase in levothyroxine dose during pregnancy 4, 5
• Starting with inadequate pre-pregnancy dosing compounds this problem 3