Isolated Maternal Hypothyroxinemia and Adverse Pregnancy Outcomes: A Systematic Review

Abstract

<jats:title>Abstract</jats:title> <jats:p>Background 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. This systematic review aimed to investigate the association between Isolated Maternal hypothyroxinemia (IMH) and adverse pregnancy outcomes. Method: PubMed, Scopus and Web of science were searched for retrieving observational studies published up to September 2019, investigating the association of IMH with adverse pregnancy outcomes. From a total of 267 articles, 15 met our eligibility criteria and were used for the purpose of the present study. Results 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. Conclusions 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.</jats:p>

Isolated Maternal Hypothyroxinemia May be Associated with Insulin Requirement in Gestational Diabetes Mellitus

“…The association was shown in the patients with IMH either in the 1st or the 2nd trimester of preg nancy. In other studies, no associations were reported between IMH and GDM [8,[18][19][20][21]. In one study analyzing IMH both in the 1st and 2nd trimester of pregnancy, IMH was found not to be asso ciated with GDM [12].…”

“…IMH may be associated with preterm birth, macrosomia, neonatal intraventricular hemor rhage, and poorer neuropsychological development in the offspring [14,15]. IMH was found to be associated also with an increased risk of GDM in some studies [8,16,17]. The association was shown in the patients with IMH either in the 1st or the 2nd trimester of preg nancy.…”

“…Also, since thy roid function has been frequently screened in pregnant women, mild thyroid dysfunctions, such as subclinical hypothyroidism and IMH, have been increasingly encountered in those [11]. The IMH prevalence has been shown to range between 1 % and 18,8 % in vari ous studies [8,12]. Hypothyroxinemia might be developed as a re sult of relative iodine deficiency, which leads the thyroid gland to produce T3 rather than T4 to preserve iodine, but also may be ob served in the iodine sufficiency state [13].…”

“…The results of studies investigating the role of overt or subclinical thyroid dysfunction in the development of GDM are contradictory [3][4][5][6][7]. In some studies, isolated maternal hypothyroxinemia was shown to be associated with the development of GDM [6,8]. Contrast findings also were reported [4].…”