Assessment of thyroid function during pregnancy: first-trimester (weeks 9-13) reference intervals derived from Western Australian women.

Objective: To establish first-trimester-specific reference intervals for thyroid function tests in pregnant Australian women.

Design, Setting And Participants: Serum samples were collected from 2159 pregnant women (9-13 weeks' gestation) attending a private pathology practice for first-trimester screening during October and November 2006. Levels of serum thyrotropin (TSH), free thyroxine (fT4), free triiodothyronine (fT3), thyroid peroxidase antibodies (TPOAb), and thyroglobulin antibodies (TgAb) were measured by chemiluminescent immunoassay (Abbott ARCHITECT analyser).