Thyroid hormones are very important for our body. They control all the cells and all important organs of the body. Pregnancy is a stressful condition and the demand for thyroid hormones increases by about 50%, because these hormones are very important for the development of fetus, therefore the gland has to increase its secretion accordingly to meet the requirement. What changes occur in thyroid gland due to pregnancy? In pregnancy, the size of thyroid gland increases by about 10% and the production of thyroid hormone increases by about 50%, therefore the blood level of thyroid hormone (TSH) in pregnant women is lower than in those women who are not pregnant. It is advisable to check TSH levels of blood in all women who are planning to become pregnant: Women in whom thyroid hormone (TSH) levels are normal she can be considered as having normal thyroid functions and therefore no treatment is needed.
Women in whom the blood report indicates hypothyroidism i.e., TSH is > 4.0mu/l and Free T4 level is low (normal range 0.7-1.9 ng/dl), thyroid replacement therapy is started. The dose of medicine (thyroid replacement hormone) is so adjusted so that the blood level of TSH is maintained less than 2.5 mu/l. If a woman, who is suffering from hypothyroidism becomes pregnant, (which can be confirmed by her home pregnancy test) she should consult the doctor because after pregnancy the need for extra thyroid hormone occurs as early as 6 weeks of pregnancy. Before birth the fetus is totally dependent on mother for the supply of thyroid hormone until the fetus own thyroid gland can start to function. Which generally does not occur until about 12 weeks of gestation (the end of the first trimester of pregnancy). By doing so we are not only treating the mother but also the fetus and also preventing complications in pregnancy. Synthetic T4 hormone or levothyroxine is the treatment of choice during pregnancy as it is exactly the same hormone as our thyroid gland produced.
Advise for a hypothyroid pregnant women: When women with hypothyroidism become pregnant they are advised tests to check the levels of TSH and Free T4 level in their blood and also to repeat the blood tests every four weeks to six weeks so that the dose of medicine can be adjusted to keep the level of TSH in the recommended range.
The recommended blood level of TSH during pregnancy is as follows: In first three months of pregnancy recommended TSH level is 0.1-2.5mu/l, must be less than 2.5mu/l, but many clinicians prefer <1 In Second trimester i.e., next three months of pregnancy 0.2-3.0mu/l In third trimester (last three months) of pregnancy 0.3-3.0 mu/l Blood TSH and Free T4 levels are useful in the diagnosis and monitoring the dose of thyroid medicine during pregnancy. If the TSH level in the blood at any time during pregnancy is more than the recommended range, then Free T4 level in the blood is checked. If T4 level in the blood is low than the dose of thyroid replacement therapy is increased. It is to be noted that only T4 hormone present in the mother’s blood can cross the placenta and is then utilized for the (neurological) development of fetus such as brain and nervous system. T3 hormone cannot cross the placenta and therefore cannot be utilized for fetal development.
Is Levothyroxine safe during pregnancy? Yes, levothyroxine (LT4) is exactly the same hormone as your natural thyroid hormone. Effects of low thyroid hormone on fetus and mother during pregnancy? If the mother is hypothyroid, she may not be able to supply her fetus with enough thyroid hormones so the fetus is at risk during the development period. The fetus is dependent on mother’s thyroid hormones during the first three months of pregnancy. Untreated, or inadequately treated, severe hypothyroidism has been associated with Low thyroid hormone levels in the mother’s blood and that may risk her pregnancy with Pre-eclampsia Anaemia. Placental abnormalities, placental abruption (separation of placenta from the wall of uterus before the birth of baby and that too prematurely thereby risking the life of baby). Low birth weight baby post partum hemorrhage (bleeding) Abortion Affect the neuro-intellectual (neurological) development of fetus. Preterm birth (when delivery occurs before 37 completed weeks of pregnancy). Neonatal respiratory distress syndrome (breathing problem that affects new born babies), developmental delays in children after birth, low IQ in the children, difficulty in schooling. Therefore it is essential that all pregnant women must be reviewed for their thyroid status, once they become pregnant and the dose of medicine must be monitored with regular the blood tests, if their reports are suggestive of hypothyroidism or reports are borderline so that the above mentioned effects can be prevented. Thyroid levels change quickly in pregnancy, so do not delay.