Is Thyroid Disorder Common in Indian Pregnant Women?

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Thyroid dysfunction is one of the most common endocrine diseases afflicting expectant women in India. Thyroid disorder significantly affects the path of pregnancy in some ways. From recent epidemiological data as well as a few clinical studies, it has been observed that thyroid complications in pregnancy, particularly hypothyroidism, in the pregnant population of India are far higher than those in Western countries. Due to the vital role played by thyroid hormones in foetal development, particularly neurodevelopment, and maternal health, this condition has already become the first concern for public health services and in the country’s obstetrics domain.

Understanding Thyroid Dysfunction

Thyroid disorder refers to the over-functioning (hyperthyroidism) or underactivity (hypothyroidism) of the thyroid gland. The most common cause of hypothyroidism is Hashimoto’s thyroiditis, and that of hyperthyroidism is Graves’ disease. The impact of pregnancy hormones and thyroid function on maternal and foetal health is alarming. The antibodies produced by the body have the effects of causing and exacerbating inflammation of the thyroid.

Magnitude of the Problem

The range of the overall prevalence of thyroid problems during pregnancy across India has varied from 13% to over 33%. This largely depends on the diagnostic criteria applied, namely, the cut-off value for Thyroid-Stimulating Hormone (TSH), and the region where the survey was carried out.

Hypothyroidism

It is to be noted 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 raised, and T4 is normal, is extremely high, with as many as 21-28% prevalence being cited in certain studies.

Hyperthyroidism

While relatively less prevalent than hypothyroidism, the frequency is 0.5%-3% in India. The incidence of hyperthyroidism in pregnancy most often calls for close monitoring, as it might be the precursor to risks like preeclampsia, preterm birth, and low birth weight.

Thyroid Autoimmunity

Positive anti-TPO antibodies (which also pose a risk of clinical disease in pregnancy) have been found to occur in almost 10-20% of Indian pregnant women.

Prevalence of Thyroid in India

A combination of nutritional, environmental, and physiological factors can explain the tremendous burden of thyroid disease in the Indian subcontinent:

Iodine Status

Despite universal salt iodisation throughout the country, certain “pockets” of India still exhibit iodine deficiency. However, excess iodine intake, common in some metropolitan areas, can also predispose to autoimmune thyroiditis.

Iron Deficiency

Iron is essential for thyroid peroxidase activity. The prevalence of maternal anaemia leading to thyroid disorder in pregnancy is undeniable. Iron deficiency can lead to defective thyroid hormone synthesis even with sufficient iodine intake.

Physiological Demand

Physiological demands for thyroid hormones during pregnancy increase by almost 50%. Women with “borderline” thyroid reserve, unable to meet this demand, are induced into subclinical hypothyroidism.

Autoimmunity

Genetically inherited causes of thyroid in pregnancy and environmental factors have led to a high prevalence of Thyroid Peroxidase antibody positivity that becomes clinically expressed under the stress of pregnancy.

Clinical Consequences for the Mother and Baby

The thyroid gland is the “master conductor” of metabolism. It serves a vital function during pregnancy, and in the first trimester, the foetus is solely dependent on maternal thyroid hormones for brain development, since the foetal thyroid is not fully developed until about the 12th week of gestation. However, if left unchecked, the impact of thyroid on the baby includes neurocognitive impairments.

Maternal Consequences

Routine thyroid test during pregnancy is vital as untreated or uncontrolled thyroid can lead to:

Consequences in Foetus

Low maternal thyroid levels are also associated with neurocognitive deficits.

General Guidelines

Given its prevalence and ‘silent’ subclinical nature, the common thyroid symptoms in pregnant women, such as fatigue, increased weight gain, or even anxiety, can easily be mistaken as induced by the pregnancy. Indian experts advocate a TSH check for every pregnant woman at the first antenatal visit.

TSH Reference Ranges across the Trimesters

Standard ‘normal’ adult range is not suitable, as during pregnancy there is increased secretion of the hormone hCG (human Chorionic Gonadotropin), which stimulates the thyroid and decreases TSH levels in pregnancy in the first trimester.

Indian guidelines recommend TSH cut-offs as:

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 synthetic thyroxine hormone (Levothyroxine), which is safe, efficacious and necessary for providing the foetus 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 at the time of pregnancy diagnosis.

Monitoring

Thyroid Stimulating Hormone (TSH) levels must be monitored every 4 to 6 weeks in the first half of pregnancy.

pregnancy guide

Conclusion

Thyroid dysfunction is a significant public health concern in India. Therefore, thyroid screening during pregnancy in India is encouraged to help preserve the neurological development of the baby.