In every human body, there is one gland called thyroid gland. Thyroid has a shaped like a butterfly, size of 2-inch-long and weighing less than 28 gram. It it located in front of the neck below the larynx (voice box), and it has two lobed, one on the either side of the windpipe. Thyroid gland is part of endocrine system which produce, store, and release hormones into the bloodstream. The hormones then travel through the body and control the activity of the body’s cell.
Thyroid gland produces two hormones, first is triiodothyronine (T3) and second is thyroxine (T4). T3 is the active hormone and made from T4. (Hoffman M, 2014)Thyroid hormones will influence and effect the brain development and growth, metabolism, heart and nervous system function brain development, body temperature, muscle strength, breathing, skin dryness, weight, menstrual cycle, and cholesterol. Hypothalamus in the brain control the pituitary gland to release thyroid stimulating hormone (TSH) which will in turn control the amount of the thyroid hormone secretes.
When thyroid hormone levels in the blood are low, the pituitary releases more TSH while when thyroid hormone levels are high, the pituitary will lower the TSH production. TSH ensures that thyroid hormone produced meet the need of the body. (McIntosh J, Jan 2 2018). Thyroid hormone control how your body uses energy, so it affect how the organ work including heart beats, how the body regulate temperature. If thyroid gland produce too much thyroid hormone, it will speed up all the functions. (Calabria A. February, 2019). Sometimes, the thyroid will not function properly where it produce too much or too little of these hormones. Too much thyroid hormone is called hyperthyroidism and can lead to many of the body’s functions to speed up while to little thyroid hormone is called hypothyroidism and lead to body functions to slow down. Thyroid dysfunction in non pregnant will give rise negative consequences for the person and if thyroid dysfunction occur in pregnant woman, it give impact in both mother and baby. (Smith A., Smith J.E, Emden, M.D, Lust K., 2017).Thyroid has many function as I mentioned earlier, however what is the role of thyroid duirng pregnancy? According to Ramprasad M. in his studied in 2012, thyroid hormones are important for normal development of the fetal during the first 3 months. It also essential for normal development of baby’s brain and nervous system, as well as other aspects of pregnancy and fetal growth. Example, either mother or fetus had suffered from hypothyroidism, the baby has a risk to get fetal disease and mental retardation. Hence. It is important that the mother has normal thyroid function during pregnancy. In the first trimester, the baby depends on the mother supply of thyroid hormone, which comes through the placenta. The baby’s thyroid will starts to work on its own at around 12 weeks. However, the baby does not make enough thyroid hormone until 18 to 20 weeks of pregnancy. The thyroid of healthy women in pregnancy will enlarged slightly, but cannot be detected in physical examination. Usually, a noticeable thyroid can be the sign of thyroid disease and should be consult to the doctor for further examination. Thyroid disease can be hard to diagnose in pregnancy because high levels of thyroid hormone in the blood. An increased amount of thyroid hormone in the blood is due to several alterations that occur in the body of pregnant women. Another factor why thyroid problem is hard to detect in pregancy is due to the symptoms is common to both pregnancy and thyroid disorder such as fatigue, increased in thyroid size and many more. During normal pregnancy, it is necessary for thyroid gland to undergo some changes in its function. Major modifications in the thyroid system during pregnancy include, first is the increased blood concentrations of T4-binding globulin (TBG). TBG is one of the proteins that transport thyroid hormones in blood, and has the greatest affinity for thyroxine (T4) of the group. Estrogen will stimulate expression of TBG in liver, and the normal increase in estrogen during pregnancy create double in the serum TBG concentrations. (Bowen R, 2012) Second, an increase in the amount of TBG in the body cause the free T4 concentrations to be decreased, which cause the pituitary to increase the secretion of TSH and consequently increase production of thyroid hormones. The new amount or net effect of TBG synthesis make a force to a new equilibrium between free and bound thyroid hormones and thus a notably increase in total T4 and T3 levels. The increased demand for thyroid hormones is get to 20 weeks of gestation and persists until term. Third is increase demand for iodine. This is due to pregnancy-associated increase in iodine clearance by the kidney caused by the increased in glomerular filtration rate and evacuate of maternal iodide by the fetus. The World Health Organization (WHO) mention to pregnant mother to increase the intake of iodine from the standard 100 to 150 microgram/day to 150 microgram/day. (Bowen R, 2012)Fourth, thyroid stimulation by chorionic gonadotropin: the placentae of humans secrete large amounts of hormone called human chorionic gonadotropin (hCG) which is very closely related to luteinizing hormone. TSH is similar like hCG that make hCG can bind and transduce signalling from the TSH receptor on thyroid epithelial cells. Toward the end of the first trimester of pregnancy in humans, when hCG levels are highest, a fraction of the thyroid-stimulating activity is from hCG. During this time, blood levels of TSH often suppressed, as depicted in the figure below. The thyroid-stimulating activity of hCG actually make some female to have transient hyperthyroidism. (Bowen R, 2012)