Thyroid Reference Ranges in Pregnancy Utilizing an Abbott Alinity Platform in a Multi-Ethnic Population in the UK.

Objective To establish new trimester-specific reference ranges for thyroid function tests - thyroid stimulating hormone (TSH), free thyroxine (fT4) and free triiodothyronine (fT3) - in a diverse multi-ethnic population using the Abbott Alinity analyser, in accordance with the 2017 American Thyroid Association Guidelines for the Diagnosis and Management of Thyroid disease during Pregnancy and the Postpartum. Design Reference ranges (defined as 2.5th-97.5th centile) were established for TSH, fT4 and fT3 from prospective samples from 663 iodine-replete healthy pregnant people with no history of thyroid dysfunction nor positive thyroid peroxidase antibodies, recruited from a large multi-ethnic urban maternity centre. Results The reference ranges for TSH were 0.06-2.73 mIU/l, 0.02-2.47 mIU/l and 0.41-2.80 mIU/l in the 1st, 2nd and 3rd trimesters. For fT4, the reference ranges were 9.9-15.3pmol/l, 8.5-14.4 pmol and 7.6-12.3 pmol/l in the 1st, 2nd and 3rd trimesters. For fT3, the reference ranges were 3.4-5.6 pmol/l, 3.3-5.5 pmol/l and 3.1-5.0 pmol/l in the 1st, 2nd and 3rd trimesters. There were no significant differences in reference ranges when the results from white and non-white participants were compared. Conclusions This study reports gestation- and trimester-specific reference ranges for thyroid function tests using the Abbott Alinity assay platform, to improve the care of pregnant people with thyroid dysfunction.