Levothyroxine (L-T4) in Fertility
Levothyroxine (L-T4) is the synthetic thyroid hormone preparation used to treat hypothyroidism, subclinical hypothyroidism, and thyroid autoimmunity in the fertility context. Clinicians dose levothyroxine to restore normal thyroid status and adjust targets based on whether the patient is attempting conception or already pregnant.
Thyroid hormone requirements begin rising within the first weeks of pregnancy and increase by roughly thirty to fifty percent overall, plateauing by about sixteen to twenty weeks. Clinicians typically raise the dose empirically as soon as pregnancy is confirmed, then guide further adjustment through serial TSH testing. Evidence for levothyroxine use in euthyroid women who are TPO-antibody positive, with a history of miscarriage or infertility, is mixed: the 2019 TABLET trial found no benefit in this broader population, and the question remains under active investigation.
Thyroid evaluation is a routine part of the RRM infertility and recurrent-loss workup, reflecting the field's root-cause orientation: clinicians treat an elevated TSH as a correctable driver of subfertility, not background noise. NaProTechnology protocols, for example, initiate levothyroxine once TSH is elevated and follow the dose with serial monitoring across the pregnancy, using tighter fertility-specific targets than general endocrine practice.
This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.