title: Update on a new controversy in endocrinology: isolated maternal hypothyroxinemia.
abstract: Isolated hypothyroxinemia (IH) is defined as a thyroxine level in the lower 5th (severe IH) or 10th percentile (mild IH) of the pregnancy-related reference range and a normal TSH. The etiology of IH remains unknown. This review aims to evaluate the biochemical criteria used to define IH in different published studies and to discuss potential maternal as well as fetal outcomes and whether treatment during early pregnancy can prevent the eventual adverse effects. For the current literature a better standardization of free thyroxine assays is needed, as well as the use of appropriated trimester-specific reference intervals for thyroid function tests. Today no study demonstrates a benefit from treating early pregnant IH women on perinatal and fetal outcomes.
authors.affiliation: Department of Endocrinology, Université catholique de Louvain, Cliniques Universitaires Saint-Luc, Avenue Hippocrate 10, 1200, Brussels, Belgium.
authors.forename: R M
authors.initials: RM
authors.lastname: Furnica
authors.affiliation: Institute of Molecular and Experimental Medicine, Cardiff University, University Hospital of Wales, Cardiff, UK.
authors.forename: J H
authors.initials: JH
authors.lastname: Lazarus
authors.affiliation: Department of Clinical Biology, Université catholique de Louvain, Cliniques Universitaires Saint-Luc, Brussels, Belgium.
authors.forename: D
authors.initials: D
authors.lastname: Gruson
authors.affiliation: Department of Endocrinology, Université catholique de Louvain, Cliniques Universitaires Saint-Luc, Avenue Hippocrate 10, 1200, Brussels, Belgium. chantal.daumerie@uclouvain.be.
authors.forename: C
authors.initials: C
authors.lastname: Daumerie
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000097:blood; D004704:Endocrinology / Q000379:methods / Q000639:trends*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D011247:Pregnancy; D011248:Pregnancy Complications / Q000097:blood* / Q000175:diagnosis*; D011256:Pregnancy Outcome; D011297:Prenatal Exposure Delayed Effects / Q000097:blood / Q000175:diagnosis; D013974:Thyroxine / Q000097:blood*
chemical_list: D015415:Biomarkers; D013974:Thyroxine
keywords: FreeT4 assays; Hypothyroxinemia; Neurodevelopmental delay; Perinatal outcome