Maternal thyroid function does not alter maternal serum α-fetoprotein interpretation

Objective: Endocrine alterations of metabolism such as diabetes and obesity are known to affect maternal serum α-fetoprotein interpretation. Thyroid function has been questioned, e.g., because of binding globulins, but not adequately studied as to its impact upon maternal serum α-fetoprotein. The purpose of this study was to assess the possible effects of T₄ and thyroid-stimulating hormone (TSH) on α-fetoprotein production, and to determine if thyroid function (hypothyroidism) alters maternal serum α-fetoprotein. Methods: We evaluated maternal serum α-fetoprotein, T4, and TSH records of 25,551 patients, between 14 and 20 weeks' gestation, on whom both studies had been ordered by the patient's primary obstetrician to rule out maternal thyroid disease in pregnancy. Statistical analyses were performed by χ₂ and regression analysis. Results: Patients were stratified according to thyroid function tests into two groups: hypothyroidism (T₄ < 6.5 μg/dL and/or TSH > 5.0 μU/mL), and normal or hyperthyroidism (T₄ ≥ 6.5 μg/dL and/or TSH ≤ 5.0 μU/mL). Maternal serum α-fetoprotein values were compared among groups for each gestational age. No significant variation or correlation of maternal serum α-fetoprotein and thyroid function was observed. Conclusions: Although other endocrine abnormalities are known to impact maternal serum α-fetoprotein values either through decreased production, decreased placental permeability, or plasma volume distribution alterations, maternal thyroid status does not interfere with proper interpretation of maternal serum α-fetoprotein.