Thyroid dysfunction is one of the most common endocrine conditions afflicting expectant women in India. Thyroid disorder significantly affects the course of pregnancy in several ways. From recent epidemiological data as well as some clinical studies, it has been observed that thyroid complications in pregnancy, especially hypothyroidism, in the Indian pregnant population are much higher than those in western countries. Because of the vital role that thyroid hormones play in fetal development, particularly neurodevelopment and maternal health, this condition has already become a top concern for the country’s public health and obstetrics services.
Understanding Thyroid Dysfunction
Thyroid disorder refers to overfunctioning (hyperthyroidism) or underfunctioning (hypothyroidism) of the thyroid gland. The most common cause of hypothyroidism is Hashimoto’s thyroiditis and that of hyperthyroidism is Graves’ disease. Its impact pregnancy hormones and thyroid function for the health of the mother and the fetus is worrying. Antibodies produced by the body result in causing and worsening thyroid inflammation.
The size of the problem
The range of overall prevalence of thyroid problems during pregnancy across India varies from 13% to over 33%. This largely depends on the diagnostic criteria applied, i.e., the cut-off value for thyroid-stimulating hormone (TSH) and the region where the investigation was carried out.
Hypothyroidism
Note that hypothyroidism in pregnancy is the most commonly occurring disease in India. While the prevalence of overt hypothyroidism, high TSH and low T4 in India has been estimated to be between 2% and 6%. That of subclinical hypothyroidism (SCH), where TSH is elevated and T4 is normal, is extremely high, with a prevalence of up to 21-28% reported in some studies.
Hyperthyroidism
Although relatively less prevalent than hypothyroidism, the incidence is 0.5%–3% in India. The frequency of hyperthyroidism in pregnancy more often requires close monitoring, as it can be a precursor to risks such as pre-eclampsia, premature birth and low birth weight.
Thyroid autoimmunity
Positive anti-TPO antibodies (which also carry a risk of clinical disease in pregnancy) have been found to occur in nearly 10-20% of pregnant women in India.
The prevalence of thyroid in India
A combination of nutritional, environmental and physiological factors may explain the enormous burden of thyroid disease in the Indian subcontinent:
Iodine status
Despite universal salt iodization across the country, some “pockets” of India are still iodine deficient. However, excessive iodine intake, common in some metropolitan areas, may also predispose to autoimmune thyroiditis.
Iron deficiency
Iron is essential for thyroid peroxidase activity. The prevalence of maternal anemia leading to thyroid disorder in pregnancy is undeniable. Iron deficiency can lead to defective thyroid hormone synthesis even with adequate iodine intake.
Normal Requirement
Physiological demands for thyroid hormones during pregnancy increase by almost 50%. Women with “marginal” thyroid reserve, unable to meet this demand, end up with subclinical hypothyroidism.
Autoimmunity
Genetic inherited causes of thyroid in pregnancy and environmental factors have led to a high prevalence of thyroid peroxidase antibody positivity that is clinically expressed under the stress of pregnancy.
Clinical consequences for mother and baby
The thyroid gland is the “main conduit” of metabolism. It serves a vital function during pregnancy, and in the first trimester, the fetus is solely dependent on maternal thyroid hormones for brain development, as the fetal thyroid is not fully developed until approximately 12 weeks of gestation. However, if left unchecked, the thyroid’s effect on the baby includes neurocognitive damage.
Maternal Consequences
Routine thyroid testing during pregnancy is vital as an uncontrolled thyroid can lead to:
Effects on the Fetus
Low maternal thyroid levels are also associated with neurocognitive deficits.
General Instructions
Given its prevalence and “silent” subclinical nature, common thyroid symptoms in pregnant women, such as fatigue, increased weight gain, or even anxiety, can easily be mistaken for pregnancy-induced. Indian experts advocate a TSH test for every pregnant woman at the first prenatal visit.
The TSH reference range varies across trimesters
The standard “normal” adult range is not appropriate, as during pregnancy there is increased secretion of the hormone hCG (human chorionic gonadotropin), which stimulates the thyroid and lowers TSH levels in pregnancy during the first trimester.
Indian guidelines recommend TSH limits as follows:
First trimester: < 2.5 mIU/L
Second/Third Trimester: < 3.0 mIU/L
Treatment
The drug of choice in treatment for thyroid in pregnancy is the synthetic thyroxine hormone (Levothyroxine), which is safe, effective and necessary to provide the fetus with adequate thyroid hormones. However, thyroid medication should be taken strictly under the guidance and consultation of a healthcare provider.
Dose
Pregnant women with pre-existing hypothyroidism usually require a 30%-50% dose adjustment immediately upon diagnosis of pregnancy.
Monitoring
Thyroid-stimulating hormone (TSH) levels should be monitored every 4 to 6 weeks in the first half of pregnancy.
Conclusion
Thyroid dysfunction is a major public health concern in India. Therefore, thyroid screening during pregnancy in India is encouraged to help preserve the baby’s neurological development.
