Isolated maternal hypothyroxinemia and adverse pregnancy outcomes: A systematic review

Fahimeh Ramezani Tehrani,Sima Nazarpour,Samira Behboudi-Gandevani

doi:10.1016/j.jogoh.2020.102057

Abstract

Maternal thyroid hormones are vital for a normal pregnancy and the development of fetus and childhood; inadequate availability of thyroid hormones during pregnancy is associated with adverse pregnancy outcomes. Isolated maternal hypothyroxinemia (IMH) is defined as a low maternal T4 in the absence of TSH elevation. This systematic review aimed to investigate the association between IMH and adverse pregnancy outcomes. PubMed, Scopus and Web of science were searched for retrieving observational studies published up to September 2020, investigating the association of IMH with adverse pregnancy outcomes. From a total of 308 articles, 17 met our eligibility criteria and were used for the purpose of the present study. Definition of IMH varied in different studies. While some studies reported no adverse pregnancy outcomes for IMH, other studies found a positive association between first trimester IMH and feto-maternal outcomes including gestational hypertension, gestational diabetes, preterm delivery, fetal distress, small for gestational age, musculoskeletal malformations, spontaneous abortion, placental abruption and macrosomia. IMH, identified in the second trimester was associated with an increase in the risk of gestational diabetes, and hypertensive disorders of pregnancy in one study. There is no consensus on the adverse effects of IMH on pregnancy outcomes. Further comprehensive cohort studies using one standard definition for IMH, with large sample size and control of important confounders such as iodine status and maternal Thyroid peroxidase antibody (TPOAb) are needed for precise assessment of this association.

Highlights

Normal fetal development is dependent on sufficient concentrations of triiodothyronine (T3)and thyroxine (T4) [1]
A comprehensive electronic literature searching was conducted independently by two authors, who were familiar with search methods and information sources, without any restrictions, in the PubMed [including Medline] and Scopus databases for retrieving original articles published in English language assessing the association between Isolated maternal hypothyroxinemia (IMH) and adverse pregnancy outcomes up to September 2019
The results of this systematic review shows that the relationship between maternal isolated hypothyroxinemia and feto-maternal and neonatal outcomes is still surrounded by many controversies, as shown by the conflicting results of studied assessed; while some studies have shown associations between IMH and adverse outcomes, others documented conflicting findings

Summary

Introduction

Normal fetal development is dependent on sufficient concentrations of triiodothyronine (T3)and thyroxine (T4) [1]. Normal fetal development is dependent on sufficient concentrations of triiodothyronine (T3). The fetal thyroid initiates iodine concentration and thyroid hormones synthesis after the first trimester of gestation [1, 2], necessitating a dependence on sufficient hormonal supplies from the mother [3]. Lack of maternal thyroid hormone availability during pregnancy is strongly correlated with adverse feto-maternal and neonatal outcomes, with a growing body of literature demonstrating that subclinical hypothyroidism during pregnancy, defined as elevated thyroid stimulating hormones (TSH) with normal levels of free triiodothyronine (fT3) and free thyroxine (fT4), during early gestation, may elevate the risk of both short and long term adverse pregnancy outcomes [4, 5]. Some literature shows that IMH is associated with adverse feto-maternal and neonatal outcomes [6, 10, 11], even cognitive function in childhood [12, 13], in despite, some data not confirming this association [14,15,16]

Methods

Discussion

Conclusion