When a woman has hypothyroidism and infertility, her fertility specialist has to weigh a number of factors in determining treatment. That decision depends partly on the type of hypothyroidism she has.
New guidelines are leading some fertility specialists to conclude that for subclinical hypothyroidism, infertility treatment might not include a thyroid pill.
Low thyroid function (hypothyroidism) can have negative impact on reproductive outcomes. Patients with overt hypothyroidism are at increased risk for infertility, miscarriage and complications with pregnancy as well as baby. Subclinical hypothyroidism (SCH) is a condition where the patient is without symptoms but the laboratory values are abnormal (thyroid stimulating hormone (TSH) levels greater than 4.5 – 5.0 mIU/L with normal free thyroxine (FT4) levels). Using these criteria, 4 – 8 % of women of reproductive age (4.6 – 8.6 million individuals) will have SCH.
Recently, the National Academy of Clinical Biochemistry (NACB) defined SCH as a TSH level greater than 2.5 mIU/L. Using these criteria, 11.8 – 14.2% of women of reproductive age (22 – 28 million individuals) will have SCH. Using NACB criteria (which were also recommended by the Endocrine Society) we at InVia Fertility Specialists have been prescribing thyroid pills (Synthroid, Levothyroxine) to patients with a TSH greater than 2.5 mIU/L. There currently is controversy regarding whether to treat subtle abnormalities of thyroid dysfunction in the infertile female patient. The question is, are we unnecessarily treating patients who really do not need thyroid pills?
The Practice Committee of the American Society for Reproductive Medicine has come up with new guidelines that review the risks and benefits of treating SCH in female patients with a history of infertility and miscarriage, as well as obstetrical and neonatal outcomes in this population.
Summary of Guidelines
- SCH is defined as a TSH level greater than the upper limit of normal range (4.5–5.0 mIU/L) with normal FT4 levels.
- The normal reference range for TSH changes in pregnancy. The upper limit of normal in most laboratories is 4 mIU/L for nonpregnant women and 2.5 mIU/L in the first trimester of pregnancy.
- This guideline was conducted because it is controversial whether or not to use first-trimester pregnancy thresholds for upper limit of TSH (i.e., >2.5 mIU/L) to diagnose and treat SCH in women attempting pregnancy.
- There is insufficient evidence that SCH (defined as TSH >2.5 mIU/L with a normal FT4) is associated with infertility.
- There is fair evidence that SCH, defined as TSH levels >4 mIU/L, is associated with miscarriage, but insufficient evidence that TSH levels 2.5–4 mIU/L are associated with miscarriage.
- There is fair evidence that treatment of SCH when TSH levels are >4.0 mIU/L is associated with improved pregnancy rates and decreased miscarriage rates.
- There is fair evidence that SCH when TSH levels are >4 mIU/L during pregnancy is associated with adverse developmental outcomes; however, treatment did not improve developmental outcomes in the only randomized trial.
- There is fair evidence that thyroid autoimmunity is associated with miscarriage and fair evidence that it is associated with infertility. Levothyroxine treatment may improve pregnancy outcomes in women with positive thyroid antibodies, especially if the TSH level is over 2.5 mIU/L.
- There is good evidence against recommending universal screening of thyroid function during pregnancy.
Recommendations by Practice Committee of ASRM
- Currently available data support that it is reasonable to test TSH in infertile women attempting pregnancy. If TSH concentrations are over the nonpregnant lab reference range (typically >4 mIU/L), patients should be treated with levothyroxine to maintain levels below 2.5 mIU/L.
- Given the limited data, if TSH levels prior to pregnancy are between 2.5 and 4 mIU/L, management options include either monitoring levels and treating when TSH >4 mIU/ L, or treating with levothyroxine to maintain TSH <2.5 mIU/L.
- During the first trimester of pregnancy it is advisable to treat when the TSH is >2.5 mIU/L.
- While thyroid antibody testing is not routinely recommended, one might consider testing anti-thyroperoxidase (TPO) antibodies for repeated TSH values >2.5 mIU/L or when other risk factors for thyroid disease are present.
- If anti-TPO antibodies are detected, TSH levels should be checked and treatment should be considered if the TSH level is over 2.5 mIU/L.
At InVia Fertility Specialists, we do plan to change our prescribing patterns for thyroid pills based on these recommendations made by the ASRM Practice Committee.
To see a fertility specialist who treats patients with state-of-the-art infertility treatment protocols, make an appointment at one of InVia's four Chicago area fertility clinics.
