| In pregnancy, the physiologic functions of the mother | | | | in neuronal multiplication, migration, and the structural |
| prior to conception are altered to provide the needs of | | | | organization of the brain of the fetus. Brain |
| the fetus growing in her womb. The placenta itself | | | | development occurs mostly during the second |
| starts producing several hormones that are vital for a | | | | trimester, wherein the fetus is yet unable to produce its |
| safe and normal pregnancy. These changes may also | | | | own fetal thyroid hormones and is largely dependent |
| affect thyroid function and thyroid screening tests. | | | | on maternal thyroid hormones for normal brain |
| One of these changes is the increase in renal blood | | | | development. |
| flow and the filtration rate of the kidneys, leading to an | | | | Evidence supports the transfer of maternal thyroid |
| increased secretion of the circulating iodides in the | | | | hormones to the fetus via the placenta before and |
| body. Normally, most of the iodides acquired through | | | | after fetal thyroid functionality. Thirty percent of the |
| ingestion of iodine-rich foods are quickly excreted by | | | | thyroxine found in the cord blood of neonates is |
| the kidney but not before the thyroid gland manages | | | | maternal thyroxine and it has been found in the |
| to “trap” about a fifth of the circulating iodides | | | | amniotic sacs of fetuses from 4 months to 6 months |
| for the production of thyroid hormones. Because | | | | in gestation. |
| normal physiologic changes gets rid of some of the | | | | Thyroid Problems in the Newborn |
| iodides before the thyroid manages to trap them, | | | | The endocrine system of the newborn is usually highly |
| dietary iodide requirements are raised to around 200 | | | | developed at the time of birth and the neonate rarely |
| micrograms per day in the pregnant woman in | | | | exhibits thyroid function problems immediately. |
| contrast to only 150 micrograms per day for normal | | | | However, in some instances, thyroid function in the |
| persons. | | | | infant must be monitored. |
| In pregnancy, the mother’s thyroid gland ordinarily | | | | One such example is that if the mother experienced |
| enlarges up to 50 percent with a corresponding | | | | hyperthyroidism or was treated with excess thyroid |
| increase in thyroxine or T4 secretion. One of the | | | | hormone during her pregnancy. If such is the case, the |
| reasons for this change is that the human chorionic | | | | infant may be born with a thyroid gland that secretes |
| gonadotropin (hCG) secreted by the placenta has a | | | | less than the normal amount of thyroid hormone due |
| stimulating effect on the thyroid. There is a broad | | | | to the excess in maternal thyroid hormone. |
| structural homology between the beta subunits of | | | | On the other side, if the mother had a thyroidectomy |
| hCG and thyroid-stimulating hormone (TSH), which | | | | or surgical removal of her thyroid gland, the child may |
| gives hCG a weak thyroid-stimulating effect. Another | | | | be born with temporary hyperthyroidism. This may be |
| hormone which may also affect the increase in | | | | because the pituitary gland of the mother secretes |
| thyroxine production by the mother is human chorionic | | | | increased amounts of thyroid-stimulating hormone due |
| thyrotropin, which is also secreted by the placenta. | | | | to her hypothyroid state. The thyroid gland of the fetus |
| Thyroid Function in the Fetus | | | | then responds to the maternal TSH and starts |
| The thyroid gland of the fetus begins to function by | | | | producing thyroid hormone in excess. |
| the end of the third month of gestation but prior to that | | | | In a fetus with a problem in thyroid hormone secretion, |
| time, the fetus is largely dependent on maternal thyroid | | | | there is poor bone development and mental |
| hormones. The fetal thyroid gland gains the ability to | | | | retardation. This may cause the condition cretin |
| produce thyroid hormones by around the eighth to | | | | dwarfism. If the newborn is not treated within several |
| tenth week of gestation. In the twelfth week of | | | | weeks, mental retardation becomes permanent. It is |
| gestation, it begins to exhibit the ability to trap iodine | | | | for this reason that newborns are routinely screened |
| actively and begins to produce thyroxine soon after. | | | | for hypothyroidism so as to prevent the devastating |
| Thyroid hormone is vital for fetal brain development as | | | | and permanent effects of cretinism. |