Thyroid hormones (T3 & T4) are produced by the thyroid gland which is a butterfly shaped gland situated in the front of the neck. The synthesis of thyroid hormone is controlled by TSH (Thyroid Stimulating Hormone) produced by the pituitary gland (master gland). The diagnosis of Hypothyroidism is based on an elevated TSH level with normal or low thyroid hormones. The production of insufficient thyroid hormones is called hypothyroidism.
Diagnosing hypothyroidism in pregnancy is a tricky task, especially in the first trimester. A pregnancy hormone, Human Chorionic Gonadotropin (HCG) is elevated in the first three months of pregnancy which mimics TSH, thus reducing the TSH levels and causing a challenge. But, it resolves by the end of the first trimester.
“In a normal pregnancy, the thyroid hormone levels (T3 & T4) are elevated because of the increase in estrogen hormone. Due to the changes in T4 & TSH levels in pregnancy there are normal ranges specified for each trimester of pregnancy (for each 3 months),” says Dr A Sharda, Consultant – Endocrinologist and Diabetologist, Manipal Hospital Millers Road. Therefore, it’s crucial to use trimester-specific ranges for total T4 and TSH when diagnosing hypothyroidism during pregnancy, to take into account the normal hormonal variations that happen in pregnancy. If the diagnosis is based on trimester-specific ranges, diagnosing the conditions is not a challenge anymore.
Diagnostic and Treatment Methods
The diagnosis of hypothyroidism is based on measuring thyroid hormones T4 and TSH levels. A TSH level is less than or equal to 2.5 mIU/L in early pregnancy is considered normal. But, a TSH higher than 10 mIU/L with a low or normal T4 level is hypothyroidism.
If the TSH level between 2.5 and 10 level it is called Subclinical Hypothyroidism. “Subclinical Hypothyroidism does not have obvious symptoms. In this situation, Thyroid peroxidase Antibodies (TPO) is checked, and if they are positive, a TSH level between 4 and 10 requires treatment. A TSH level between 2.5 and 4 can be observed by checking in 2 to 4 weeks. The diagnosis can be missed if it is based only on symptoms of hypothyroidism like constipation, tiredness, sleepiness, etc. as it can overlap with pregnancy symptoms,” adds Dr Sharda.
The treatment for hypothyroidism is levothyroxine (a synthetic form of thyroid hormone T4). This tablet has to be taken orally on an empty stomach. A gap of 45 minutes should be given before taking any other food or drinks. Generally, calcium and iron supplements are given during pregnancy. As these interfere with the absorption of thyroid tablet they should be taken at least 4 to 6 hours later.
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Is it essential to diagnose hypothyroidism early during pregnancy?
It is important to treat hypothyroidism early in pregnancy because thyroid hormones are important for the development of the baby especially for brain and neuromuscular system. “Severe hypothyroidism can result in complications for both the mother and the baby, such as pre-eclampsia, maternal anaemia, congestive heart failure, post-partum hemorrhage, miscarriage, premature delivery, and developmental problems in the baby,” opines Dr Sharda.
Checking thyroid levels is important for pregnant women, especially if they have risk factors like personal and family history of thyroid disease, have a positive TPO antibody earlier, and other auto-immune disease like Type 1 Diabetes, and age over 30 years, infertility etc. These simple measures go a long way in ensuring a healthy baby and mother, even in the presence of hypothyroidism.
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