What Are the Maternal Hormones?
Hormones from the mother carrying the baby are called maternal hormones. Some chemicals can pass through the placenta (an organ developed during the pregnancy which provides oxygen and nutrients to the baby) into the baby's blood during the pregnancy. For example, in pregnant women, hormones can change the mother's body due to the production of high levels of estrogen, which causes breast enlargement in the mother. Maternal thyroid dysfunction has been associated with a child's brains motor (physical) and cognitive (mental) disabilities based on the number of thyroid hormones in the brain development of the fetus and occurs mostly during the first half of the gestation (between conception and birth) period when the fetal functions depend on the maternal thyroid supply.
Changes in the growing fetal brain and its development were seen when there are disturbances in the maternal hormones (hormones from the mother). Thyroid hormones are essential hormones for normal brain development. The thyroid plays a vital role during the early development process of growth. The stages of growth are listed below:
- Fetus.
- The placenta.
- Differentiation of developing fetal tissues.
- Including the brain.
Congenital hypothyroidism (thyroid hormone deficiency present at birth) is associated with several neurological damages causing intellectual disabilities (including difficulty in understanding, memory, communication, problem-solving, physical skills, and emotional skills). Thyroid-stimulating hormone (TSH) is the most accurate indicator for detecting thyroid function during pregnancy. The mother's hormonal levels of thyroxine (T4) during the first trimester are the major hormone responsible for postnatal psychomotor (physical skills) development, for example, by a self-driving car, playing, typing, operating a machine, playing an instrument, and throwing a ball.
Maternal hypothyroxinemia (decreased thyroxine with normal thyroid stimulating hormone) at the beginning of the neurogenesis (formation of neurons during brains development) can cause a higher risk of language expression and non-verbal cognitive (conscious mental activities such as thinking, remembering, imagining, etc.) delays in the babies. Corticosteroids (anti-inflammatory medicine) suppress the increase in cell production and stimulate communication with others for the maturation of the fetal organs. Within the uterus exposure to stress or high levels of glucocorticoids (a type of corticosteroids), endogenous (internal cause), or synthetic molecular and structural impacts on the development of the brain, and also appears to weaken or damage the mental process and increase reaction to stress and anxiety.
How Is Maternal Prenatal Stress and HPA Axis Related to Fetal Brain Development?
Chronic stress-related dysregulation of these HPA (hypothalamic-pituitary-adrenal) axes can affect all the endocrine (organs and glands secreting hormones) systems, including the gonadal (hormones involved in reproduction and other functions of the body) and thyroid axes. Stress hormones may stop producing these axes at several levels, where the estradiol (estrogen and major female sex organ) and the thyroid hormones stimulate the stress systems. Glucocorticoids (a type of corticosteroid) may facilitate energy conversion during stress. Glucocorticoids of the HPA (hypothalamic pituitary adrenal) axis may participate in the maturation and the central nervous system development. Which occurs through structural, functional, and neurochemical procedures.
Fetal circulation through the placenta is important during neurodevelopmental processes, such as remodeling the dendrites (finger-like cells present on the end of the neuron) and axons in neuronal and glial (nerve) cells in the brain area of the fetus. Maternal stress and elevated levels of glucocorticoids can cause epigenetic (behavior and environmental changes affecting the genes) alterations related to increased cardiovascular tone, reduced insulin, increased glucose production, and fat. The environmental events may interfere with the chromatin (mixture of chromatin and DNA) structures and DNA methylation (chemical reaction in the body by adding methyl to DNA, protein, and molecules) and thus affect the glucocorticoid receptor gene expression.
How Is Maternal Prenatal Stress Related?
Placental function is critical. Since it is important for fetal and maternal interactions to participate in hemostasis. One of its main functions is to control fetal exposure to maternal cortisol. The hormone controls the active cortisol into inactive cortisol. The impact of maternal stress can be seen on the placenta and endocrine functions by causing an interruption in the production of neurotrophins (regulate the function of the vertebrate nervous system) and neurotransmitters (the body's chemical messengers without which the body cannot work) that play a key role in fetal neural development. Maternal stress is associated with placental hypoxia (insufficient oxygen) due to the restricted flow in the umbilical artery (which carries deoxygenated blood from the fetal circulation to the placenta), which interrupts the normal neuronal (nerve cells) migration and the myelination process (a specialized membrane for the cell communication used to increase the speed signals between the neurons).
How Are HPT Axis and TH Related to Fetal Brain Development?
The paraventricular nucleus of the hypothalamus (one of the most important autonomic control centers of the brain) seen in the parvocellular region (carries the information about slow, colorful things) responsible for the synthesis and secretion of thyrotropin-releasing hormone, which stimulates the secretion of thyroid-stimulating hormone from the anterior pituitary. The fetus collects the iodine and synthesizes thyroid hormones by the 11th and 12th week of pregnancy then the thyroid secretion begins around the 16th week. Because of this, fetal thyroid production is not completely matured during intrauterine life. Thyroid deficiency in the embryonic stages impacts the developing brain not only in functional and molecular ways but also in the morphology of the brain regions such as the cerebral cortex, hypothalamus, and cerebellum. In maternal hypothyroidism, there is limited growth of the axons seen. In maternal hyperthyroidism, it accelerates neurodevelopmental procedures that can lead to the early development of the brain, where brain tissue weight is decreased.
What Are the Other Factors That Affect Fetal Brain Development?
Factors affecting fetal brain development are listed below:
-
Nutrition - Both maternal and overnutrition have consequences for fetal development. The effects of maternal undernutrition have been characterized in individuals who are exposed to severe undernutrition in the uterus. Pregnant women have an estimated calorie intake of about 400 to 800 per day for a five to six-month period. Increased incidence of chronic heart disease and diabetes type 2 in the developing pregnancy.
-
Infection - Pregnant women are more susceptible to infection and display an increased inflammatory response for some pathogens, but the mechanism is unknown. Maternal viral infections during pregnancy can increase psychiatric diseases in the offspring. Maternal exposure to measles, rubella, and polio increases the risk of developing schizophrenia (a type of mental disorder) in the offspring. Other infections, like genital herpes, that may affect neurodevelopment by increasing the risk of preterm birth are independently associated with adverse neural development. Vertical transmission of viral pathogens to the fetus can be associated with serious neurodevelopmental consequences. Zika and cytomegalovirus during the first trimester have been associated with microcephaly (babies' heads are much smaller than expected). Bacterial infection during the second trimester and ASD (autism spectrum disorder) cause poor neural development in the baby.
-
Maternal Stress - Stress is an imbalance between the environment and an individual's perception of their resources to manage the environment. Prenatal stress affects cognitive development in the child. Babies associated with high prenatal maternal stress or anxiety are at higher risk of developing depression.
Conclusion:
Factors such as poor nutrition, stress, and infection during pregnancy were associated with adverse effects on fetal neural development. Maternal hormones have ideal and harmful effects on fetal and brain development. One should improve fetal neural development by maintaining maternal hormones. Thyroid hormones and cortisol influence fetal neural development.
