**8. Factors influencing thyroid functions in pregnancy**


**5.** Increased urinary excretion of iodine in pregnancy impairs thyroid hormone production. This in turn leads to goiter, maternal, and fetal hypothyroidism. Maternal hypothyroidism is seen in 2–3%. Thyroid hormone requirement increases by 25–50 μg/day.

**Chapter 2**

**Provisional chapter**

**Congenital Hypothyroidism**

**Congenital Hypothyroidism**

http://dx.doi.org/10.5772/intechopen.81129

infant treated with T4 alone.

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

DOI: 10.5772/intechopen.81129

Congenital hypothyroidism is one of the commonest preventable causes of mental retardation is also the most common congenital endocrine disorder of childhood. The subtlety of clinical features and protective effect of the maternal hormone on fetal brain after crossing the placenta mask the clinical features. The incidence varies from 1 in 4000 to 1 in 1000 in newborn infants in various parts of world and is increasing worldwide. Thyroid agenesis remains the most common etiology of CH and other causes are dyshormonogenesis, defects in peripheral thyroid hormone transport, metabolism, or action. CH is usually diagnosed after neonatal screening tests and if treatment started with in few weeks of birth neurodevelopmental outcome is usually normal. Levothyroxine (T4) remains the treatment of choice as most brain T3 is derived from local monodeiodination of T4 and studies have shown normal serum level of T3 in

Congenital hypothyroidism (CH), one of the commonest preventable causes of mental retar dation is also the most common congenital endocrine disorder of childhood [1]. Neurodevelopmental outcome is usually better if treatment is started within in few weeks of birth [2]. The subtlety of clinical features and the maternal hormone crossing the placenta provides a protective effect on the fetal brain masking the clinical signs [3]. In addition to this even the most severe forms of CH have some functioning residual thyroid tissue further making clinical diagnosis difficult [4]. As the age of the neonate progresses so does the hypothyroxinemia leading to progression of the clinical signs and symptoms which increases the risk for irreversible brain injury. To prevent this, treatment needs to be started as soon as possible after

**Keywords:** congenital, hypothyroidism, levothyroxine, TSH, thyroid

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Sanjay Saran

Sanjay Saran

**Abstract**

**1. Introduction**

The current open access book on thyroid disorders covers many interesting topics. On the whole, various titles are interesting and provide additional information. I am sure this online book on thyroid disorders will be read by readers with great enthusiasm.
