Maternal thyroid function at 11-13 weeks of gestation in fetal trisomies 21 and 18.

OBJECTIVE To examine the association between maternal serum levels of thyroid stimulating hormone (TSH) and free β-human chorionic gonadotrophin (free β-hCG) in trisomy 21, trisomy 18 and euploid pregnancies at 11-13 weeks and investigate the potential value of TSH in first-trimester screening for aneuploidies. METHODS Maternal serum TSH and free β-hCG levels at 11-13 weeks in 25 trisomy 21 and 25 trisomy 18 pregnancies were compared with levels in 3592 unaffected pregnancies. Only women with no history of thyroid disease and negative for antithyroid antibodies were included. RESULTS Serum TSH in the trisomy 21 pregnancies was lower [0.76 multiples of the normal median (MoM), interquartile range (IQR) 0.46-1.09 MoM] and in trisomy 18 it was higher (1.25 MoM, IQR 0.88-1.98 MoM) than in unaffected pregnancies (1.01 MoM, IQR 0.61-1.51 MoM). There were significant associations between TSH and free β-hCG in the unaffected pregnancies (r = - 0.214, p < 0.0001), but not in those with trisomy 21 (r = - 0.157, p = 0.452) or trisomy 18 (r = - 0.176, p = 0.401). CONCLUSIONS hCG, rather than TSH, may be the primary thyrotropic factor in early pregnancy. Measurement of TSH does not improve the performance of screening for trisomies 21 and 18 provided by nuchal translucency, free β-hCG and pregnancy-associated plasma protein-A.