Myths vs facts: TSH Schilddrüse and fertility

Thyroid function is linked to fertility, but TSH levels are often misunderstood. A TSH above 4.0 mU/l (overt hypothyroidism) clearly disrupts ovulation and reduces conception rates. A common myth is that any TSH above 2.5 requires treatment when trying to conceive. The evidence is moderate: the American Thyroid Association suggests a target TSH below 2.5 for women planning pregnancy, based on observational data. However, randomized trials have not consistently shown improved fertility or pregnancy outcomes from levothyroxine in subclinical hypothyroidism (TSH 2.5–4.0). Another myth is that a 'normal' TSH guarantees good fertility – in reality, thyroid autoimmunity (TPO antibodies) can impair fertility even with normal TSH. TSH alone is insufficient; free T3, free T4, and antibodies are needed for full assessment. The fact is: overt hypothyroidism (TSH >4.0) is a well-established fertility risk, while subclinical elevations are a gray area. Individual variation, cycle phase, and iodine status also matter. A home TSH test can give a hint but should not replace clinical evaluation. Evidence rating: human-moderate – associations are clear, but interventional data are limited.