Hypothyroidism in pregnancy
DOI:
https://doi.org/10.18597/rcog.443Keywords:
hypothyroidism, thyroid, pregnancyAbstract
Introduction: hypothyroidism is present in 0.5-2.5% of all pregnancies. Frequency becomes greater when considering risk populations (i.e. patients who are carriers of other autoimmune diseases). A foetus depends on maternal thyroid products during early gestational stages because its thyroid gland is not able to release its products until the end of the first trimester. Impaired thyroid function or iodine deficiency could thus exert undesirable effects on the foetus during the embryogenic period.
Objective: the present work is aimed at reviewing some aspects of the physiology of the thyroids and hypothyroidism during pregnancy, how to evaluate it, its management and prognosis.
Materials and methods: a bibliographic search was made of electronic databases (Medline, Cochrane) and printed material, selecting articles considered by the authors to be of greater scientific and epidemiological relevance. Material published from 1990 to 2007 was consulted.
Discussion: pregnant women have well-defined physiological thyroid changes, such as thyroid enlargement, increased thyroid binding globulin (TBG) in response to increased oestrogen production and transient first trimester hyperthyroidism caused by increased human chorionic gonadotrophin (HCG). These adaptations occur because of maternal interaction with the foetus and placenta; however, women maintain normal thyroid function during normal pregnancies.
Considering such adaptation mechanisms, thyroid function during pregnancy must be evaluated by determining thyrotrophin (TSH) and free thyroxine (free T4); anti-thyroid antibody detection is also useful in some cases.
High doses must be used in substitutive therapy to maintain free T4 level at the normal upper limit from the time diagnosis is established. Patients having a previous diagnosis of hypothyroidism will usually need dose adjustment, generally increasing levothyroxine by 25% to 50%.
Patients having positive auto-antibodies during first trimester, especially antiperoxidase auto-antibodies (ATPO) have more risk of transient or permanent post-partum thyroid disease and greater psychiatric symptomatology prevalence. Puerperal follow-up is recommended in such patients.
Author Biographies
Carla Lorena Macchia
Javier Augusto Sánchez Flórez
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