- Thyroid hormones during pregnancy and fetal development
Thyroid hormones during pregnancy perform a critical function in brain development in the fetus and newborn, as well as in many other aspects of pregnancy and growth of the unborn child. Hypothyroidism (decreased thyroid hormone levels in the blood) in both the mother and the fetus, often leads to diseases of the child; people one of the most common and serious complications of this disorder is a mental retardation
Mental retardation - if the mind is underdeveloped
The functioning of the thyroid gland during pregnancy
All animals during pregnancy thyroid undergoes significant changes. This phenomenon is the most thoroughly studied in humans, but you are likely to assume that it also manifests itself in all mammals. The most significant changes related to the activity of the thyroid gland in pregnancy:
Increasing the concentration of thyroxine binding globulin (TBG) in the blood. TSH - one of the few proteins that is responsible for transporting thyroid hormones; of these proteins it is most avidly binds to thyroxine
Thyroxine - the main thyroid hormone
(T4). Estrogen stimulates the expression of the TSG in the liver and increase the natural levels of estrogen
Estrogen - the key to bone health
during gestation induces an increase in the concentration of TSH in the blood approximately twice.
Increased TBG reduces the concentration of free thyroxine, resulting in increased secretion of thyroid stimulating hormone (TSH) by the pituitary. As a result, the body begins to produce more thyroid hormone. The main objective of increasing the concentration of TSH - to achieve a new equilibrium between free and bound thyroid hormones and as a result, a significant increase of thyroxine and triiodothyronine (T3) in the blood, as they are necessary for the development of the child. In normal thyroid hormone levels reach the required approximately the twentieth week of pregnancy, and does not change until delivery.
Increased demand for iodine. This is due to a significant increase in renal clearance of iodine (in other words, kidneys faster than before pregnancy purify body fluids of iodine is caused by an increase in glomerular filtration rate in pregnant women), and the fact that now the mother requires iodine not only for themselves but also for the child . Experts of the World Health Organization recommend that pregnant women increase the intake of iodine with a standard dose of 100-150 micrograms (mcg) per day to 200 micrograms per day.
The stimulation of the thyroid gland of human chorionic gonadotropin. The placenta of humans and other mammals secrete large amounts of a hormone called human chorionic gonadotropin (in humans is - human chorionic gonadotropin, hCG), very similar to luteinizing hormone. TSH, and hCG are so similar that hCG can bind to the TSH receptor and transmit signals to epithelial cells of the thyroid gland. By the end of the first trimester of pregnancy when hCG levels are highest, a significant part of the process, during which the stimulation of the thyroid gland takes the HCG. During this period the level of TSH in the blood tends to be lowered. Due to the fact that hCG stimulates the production of thyroid hormones, some women early in pregnancy develops temporary hyperthyroidism.
In general, the need for the organism (more precisely, two organisms) in thyroid hormones in pregnant women increases. And if it does not normally cause any problems, women with weak hypothyroidism during pregnancy on thyroid hormone deficiency can be a serious problem.
TSH levels during pregnancy
A recently published study provide important information for women with thyroid disease who are planning to become pregnant in the future, or are already pregnant. Key points of the report on the results of the study:
- Disorders of the thyroid gland - including subclinical - associated with the risk of complications during pregnancy, as well as short and long term health problems for the mother and the child.
- The highest risk of complications for women with autoimmune thyroid disease, even if the thyroid hormone levels are normal.
- Women with elevated levels of thyroid stimulating hormone (TSH) is three times higher risk of premature birth.
- Women with positive results analysis antitireoglobulin (ATG), the probability of preterm delivery compared with the normal increased twice.
Women who undergo hormone replacement therapy of the thyroid gland, in the first weeks of pregnancy is necessary to increase the dose of drugs taken by 30-60%. Probably during the next term of pregnancy for these patients will be advised to take a dose, 50% percent higher than the one that was recommended prior to pregnancy.
The normal TSH levels during pregnancy
During normal pregnancy, women consume adequate amounts of iodine, which has no ATG in the blood should be following parameters TTG:
- First trimester: 0.24 - 2.99;
- Second trimester: 0.46-2.95;
- Third trimester: 0.43 - 2.78.
Thyroid hormones and brain development in the fetus
Yet in 1888 the London society of clinicians has issued a report which highlighted the importance of the proper functioning of the thyroid gland for the development of the brain. Since then, numerous studies on rats, sheep and humans have confirmed this concept; particularly active for many years studied the effects of thyroid hormone deficiency
Deficiency of thyroid hormone - revealed a previously unknown reason
in the mother and / or fetus. All data suggest that thyroid hormones exert profound influence on the course of the last stage of differentiation of the brain, including, for synaptogenesis, the growth of dendrites and axons, myelination and neuronal migration.
Thyroid hormones bind to receptors by nuclear and stimulate transcription of genes responsinyh. In the brain of the fetus very much thyroid hormone receptor, and they appear there before the fruit begins to synthesize thyroid hormones. Despite the long, complex investigation it was surprisingly difficult to determine what exactly the molecule affect thyroid hormones in the developing brain, but by now this is something well known. For example, the promoter of myelin basic protein gene reacts directly with the effects of thyroid hormones. This corresponds to the received data from studies that hypothyroidism can decrease the production of certain proteins associated with myelin.
Today it is obvious that scientists still have a lot of work to better understand the molecular mechanisms by which thyroid hormones maintain normal development of the fetal brain.