This is an important question and the answer is clear: your wife's gynecologist is correct in prescribing Levothyroxine 12.5 mcg. Here is why. While TSH 3.75 µIU/mL is within the normal population reference range (0.4–4.5), the target is DIFFERENT for women who are planning to conceive. According to current guidelines from the American Thyroid Association and Indian endocrinology guidelines on preconception thyroid management, the recommended TSH target before and during pregnancy is below 2.5 µIU/mL in the first trimester and preconception period. Your wife's TSH of 3.75 is above this preconception target. A higher-than-ideal TSH (even if 'technically normal' for the general population) in early pregnancy has been associated with increased risk of miscarriage, reduced fertility, and impaired fetal brain development. The dose of 12.5 mcg (which is the smallest available dose of Thyronorm) is very safe, very low, and specifically calibrated to bring the TSH down to below 2.5 without causing hyperthyroidism. The negative Anti-TPO antibody is reassuring — it means there is no underlying autoimmune thyroid disease — but preconception TSH optimization is still recommended. The second doctor who questioned this advice was likely applying the standard general population range, not the stricter pregnancy-specific range.

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For preconception period and during pregnancy, target TSH is 2.5- 3 So if she is planning to conceive you have to get the optimum TSH level But as you are taking Novelon now, so pregnancy is not possible for coming 3months So better to get TSH tested after 2months and to start medicine if it is still above 3 But much said your gynaecologist should be trusted with his/her opinion

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As you're planning for conception, tsh should be less than 3 So continue medicines

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Plan pregnancy once TSH level is below 3

TSH preconceptionally should be less than 2.5 Your wife needs to take thyroid medication to achieve euthyroid levels