Do women with borderline (subclinical) hypothyroidism who are struggling to conceive need to have their thyroid levels optimised? Untreated, or undertreated, hypothyroidism can make it harder to conceive and can result in poorer pregnancy outcomes. However, the evidence about the effect of borderline (subclinical) hypothyroidism on fertility is less clear-cut. If you have a diagnosis of subclinical hypothyroidism, and are not currently being treated for it with levothyroxine (L-T4), you should have a TSH measurement performed as soon as possible to see whether you need to start treatment. The tables below provide a guide to the treatment of women with subclinical hypothyroidism not currently being treated with levothyroxine (L-T4): Thyroid peroxidase antibodies (TPO Ab) positive TSH greater than reference range Treatment with L-T4 recommended TSH above 2.5 but less than reference range Consider treating with L-T4 TSH less than 2.5* Don’t treat TPO Ab negative TSH greater than 10 Treatment with L-T4 recommended TSH above reference range but less than 10 Consider treating with L-T4 TSH less than reference range (or less than 4.0)* Don’t treat *Some fertility clinics may treat people with a TSH greater than 2.5 mIU/L regardless of antibody status, but there is no real hard evidence for this. If you are already receiving L-T4 treatment for overt hypothyroidism (or subclinical hypothyroidism), it is generally recommended that your levothyroxine is increased immediately after your pregnancy is confirmed, usually by 25-50mcg daily. This is most easily achieved by doubling your current dose on two days of the week. You should then contact your GP and arrange to have a thyroid blood test . See our pregnancy and thyroid disorders alert card Manage Cookie Preferences Please ensure Javascript is enabled for purposes of website accessibility