Thyroid and Pregnancy — Everything You Must Know Before Conceiving

Why the thyroid matters so much for pregnancy: The thyroid produces T3 and T4 hormones that regulate metabolism — but in pregnancy, these hormones are also critical for fetal brain development, placental formation, and maintaining the uterine lining. Hypothyroidism (underactive thyroid): - Causes irregular or absent ovulation - Increases miscarriage risk by 2–3x - Impairs embryo implantation - Can affect fetal neurological development if untreated in early pregnancy - Even subclinical hypothyroidism (TSH 2.5–4.0) in women trying to conceive is associated with poorer outcomes Target TSH for conception and early pregnancy: - Trying to conceive: TSH < 2.5 mIU/L - First trimester: TSH < 2.5 mIU/L - Second trimester: TSH < 3.0 mIU/L - Third trimester: TSH < 3.5 mIU/L - These are stricter than the general population normal range (0.5–4.5) Hyperthyroidism (overactive thyroid): - Causes irregular periods and early pregnancy loss - Requires treatment before conception (antithyroid medication, dose adjusted carefully) - Graves' disease antibodies can cross the placenta — requires monitoring Hashimoto's thyroiditis: - Autoimmune condition causing hypothyroidism - TPO antibodies associated with higher miscarriage rate even when TSH is normal - Dr. Ankita monitors TPO-positive patients closely regardless of TSH value Dose adjustment in pregnancy: - Most women on levothyroxine need a 25–30% dose increase by Week 6–8 of pregnancy - TSH must be rechecked every 4–6 weeks in first trimester - Missing doses in early pregnancy has real consequences — do not skip