The thyroid is a butterfly-shaped gland that sits at the front of the neck, just below the Adam's apple. It produces two main hormones — T3 (triiodothyronine) and T4 (thyroxine) — which together control the speed of your metabolism: how fast you burn calories, how warm you feel, how regularly your bowels move, how steadily your heart beats and how your mood and energy settle through the day.

Thyroid output is regulated by a feedback loop with the pituitary gland in the brain. The pituitary releases TSH (thyroid stimulating hormone) — when thyroid levels are low, TSH goes up to push the gland harder; when thyroid levels are high, TSH drops. This is why a TSH blood test is the single most useful screening number, even though it does not directly measure thyroid hormone itself.

Crucially for fertility, thyroid hormones also interact closely with the reproductive system — they influence ovulation, menstrual cycle length, prolactin levels and the lining of the uterus. When the thyroid is out of range, the reproductive system often shows it first, sometimes long before the more familiar symptoms appear.

Indian community surveys consistently show that around 11 percent of adult women have a diagnosed thyroid disorder, with hypothyroidism (an underactive thyroid) far more common than hyperthyroidism. Subclinical hypothyroidism — a raised TSH with otherwise normal hormone levels — is even more widespread and often missed because the symptoms are vague.

Several factors push the Indian numbers high: autoimmune thyroid disease (especially Hashimoto's), historical iodine deficiency in certain regions, post-pregnancy thyroid changes and a strong genetic component that runs in families. Urban women are diagnosed more often partly because they are tested more often, but rural prevalence is also significant.

The practical takeaway for anyone trying to conceive is simple: thyroid testing is not optional curiosity — it is a basic part of the fertility workup in India, and a single TSH blood test will catch most of the important cases.

• Symptoms: weight gain that resists effort, cold intolerance, persistent fatigue, dry skin, constipation, hair loss or thinning, and heavy or irregular menstrual periods.
• Cognitive and mood changes: brain fog, low mood, poor concentration and a general slowing-down that is easy to mistake for stress or normal tiredness.
• Commonest cause: Hashimoto's thyroiditis, an autoimmune condition where the body's own antibodies gradually damage the thyroid gland — confirmed by anti-TPO antibodies on a blood test.
• Other causes: iodine deficiency, history of thyroid surgery or radioactive iodine, certain medicines such as lithium and amiodarone, and a strong family history of thyroid disease.
• Many women have no dramatic symptoms — only a slightly raised TSH on a routine test — which is exactly why TSH is checked early in any fertility workup.

• Symptoms: unexplained weight loss, fast or pounding heartbeat (palpitations), heat intolerance, sweating, tremor of the hands, anxiety, restlessness and difficulty sleeping.
• Menstrual changes typically run the other way: lighter, shorter or less frequent periods, sometimes with reduced fertility because ovulation becomes irregular.
• Commonest cause: Graves' disease, an autoimmune condition where antibodies overstimulate the thyroid — often associated with eye changes (puffy eyes, staring look) and a visible neck swelling (goitre).
• Other causes: a single overactive thyroid nodule or a multinodular goitre producing excess hormone, and (less commonly) early postpartum thyroiditis.
• Hyperthyroidism is less common than hypothyroidism but more dangerous if missed during pregnancy, so a low TSH on screening always needs follow-up testing.

Untreated hypothyroidism disrupts fertility through several mechanisms at once. It often raises prolactin (the milk hormone), which directly suppresses ovulation. It shortens the luteal phase of the cycle, leaving too little time for a fertilised egg to implant. It alters the quality of cervical mucus and the receptivity of the uterine lining. In women who are ovulating and conceiving, untreated hypothyroidism roughly doubles the risk of first-trimester miscarriage and increases the risk of preterm labour, preeclampsia and lower IQ in the baby.

Untreated hyperthyroidism causes its own pattern: faster metabolism, weight loss, lighter periods and often anovulation. In pregnancy, uncontrolled hyperthyroidism raises the risk of miscarriage, preterm birth, low birth weight and a serious complication called thyroid storm.

The reassuring news is that all of these risks come down sharply once the thyroid is brought into range. Well-controlled thyroid disease, whether hypo or hyper, is fully compatible with normal fertility and a healthy pregnancy. The risks belong to untreated disease, not to the diagnosis itself.

• Pre-conception (actively trying or planning within the next few months): TSH below 2.5 mIU per litre is the widely accepted target in India, per FOGSI and endocrine society guidelines.
• First trimester of pregnancy: TSH below 2.5 mIU per litre, ideally already in range before conception so the early weeks are protected.
• Second and third trimesters: TSH below 3.0 mIU per litre — a slightly more relaxed but still tight target, reflecting normal pregnancy physiology.
• If your TSH is above target on your first test, do not panic — most women reach target within 6 to 8 weeks of starting or adjusting levothyroxine, and conception is usually possible during this period too.
• These targets apply equally to women on levothyroxine and to women not yet on treatment. The number on the report is what matters; the path you take to get there is between you and your doctor.

• TSH (thyroid stimulating hormone): the single most important screening test, ₹200 to ₹500 in most Indian labs — abnormal values trigger further testing.
• Free T4 (free thyroxine): measures the active hormone level, ₹250 to ₹500 — useful when TSH is abnormal to confirm and grade the problem.
• Anti-TPO antibodies: ₹500 to ₹1500 — confirms autoimmune Hashimoto's as the cause, which matters because positive antibodies raise miscarriage risk even when TSH looks borderline.
• Combined TFT (thyroid function test) panel: ₹400 to ₹1500 — usually bundles TSH, free T3 and free T4, and is the most convenient first test in most fertility workups.
• Trusted Indian laboratory networks include Thyrocare, Metropolis, SRL Diagnostics and Dr Lal PathLabs, with home-collection options widely available across major cities.
• Repeat testing: once on treatment, TSH is rechecked every 6 to 8 weeks until stable, then every 3 months in pregnancy and yearly thereafter.

For hypothyroidism, treatment is a daily tablet of levothyroxine — sold in India as Eltroxin, Thyronorm and several generic brands at around ₹30 to ₹200 a month. The tablet must be taken on an empty stomach, 30 to 60 minutes before food or tea, because food (especially calcium, iron and soy) blocks absorption. Most women take it first thing in the morning with plain water; some prefer bedtime, at least three hours after dinner.

Doses are adjusted by repeat TSH testing every 6 to 8 weeks until target is reached, then less frequently. Importantly, levothyroxine should be continued through pregnancy — and the dose almost always increases by 25 to 30 percent in early pregnancy, often before the first antenatal visit. If you become pregnant on levothyroxine, contact your doctor within the same week rather than waiting for the next routine check.

For hyperthyroidism, treatment is more nuanced. The main oral medicines are methimazole or carbimazole (Neomercazole, Carbimazole) and propylthiouracil (PTU). In pregnancy, PTU is the preferred choice in the first trimester, with a switch to methimazole later. Radioactive iodine treatment is strictly avoided during pregnancy and for several months before TTC. Surgery (thyroidectomy) is reserved for specific indications. All hyperthyroidism in pregnancy needs joint care with an endocrinologist.

Iodine is the raw material the thyroid uses to make T3 and T4, so adequate intake is essential — especially in pregnancy. India has a long-running national salt iodisation programme (since 1992), and iodised salt is now mandatory for human consumption. Always check the salt packet label and choose iodised salt for regular household cooking.

Daily iodine requirements are about 150 micrograms for adults and 250 micrograms during pregnancy and breastfeeding — an extra 100 micrograms over baseline, which a regular Indian diet with iodised salt usually meets. Some prenatal vitamins also include iodine; check the label.

Crucially, more is not better. Excess iodine — from large doses of seaweed, kelp tablets or unsupervised supplements — can itself trigger thyroid dysfunction and worsen autoimmune thyroid disease. Iodine supplements should only be taken on a doctor's specific advice, never as a do-it-yourself fertility hack.

Postpartum thyroiditis is a thyroid inflammation that appears in the first year after delivery, affecting roughly 5 to 10 percent of Indian women. The classical pattern is a hyperthyroid phase between 2 and 6 months (anxious, sleepless, palpitations, weight loss — easy to mistake for new-parent stress) followed by a hypothyroid phase between 6 and 12 months (fatigue, weight gain, low mood — easy to mistake for postpartum depression).

Many women, and many doctors, miss this pattern entirely because the symptoms look like ordinary postpartum life. A simple TSH test at the 6-week postnatal visit and again at 6 months catches most cases. If you have a history of thyroid disease, autoimmune disease or a previous postpartum thyroiditis, screening becomes even more important.

Postpartum thyroiditis often resolves on its own, but a significant number of women need temporary or permanent levothyroxine treatment — and those who recover fully still carry a higher lifetime risk of hypothyroidism. If your next pregnancy is being planned soon, a pre-conception TSH is wise. If you have already had a loss and a history of thyroid disease, miscarriage types and recovery in India is a gentle next read.

• Myth: "Thyroid means I cannot get pregnant." Fact: Well-controlled thyroid disease is fully compatible with normal fertility and a healthy pregnancy — the risk belongs to untreated disease, not the diagnosis.
• Myth: "Levothyroxine will help me lose weight." Fact: Levothyroxine treats the cause of weight gain in true hypothyroidism but is not a weight-loss drug and is dangerous if taken without thyroid disease.
• Myth: "Once my TSH is normal I can stop my thyroid medicine." Fact: For most causes (especially Hashimoto's), the thyroid does not recover — stopping the tablet means the TSH will rise again within weeks.
• Myth: "Eating more iodine will fix my thyroid." Fact: Iodine deficiency and Hashimoto's are different problems; extra iodine can actually worsen autoimmune thyroid disease.
• Myth: "I should wait until after pregnancy to start treatment." Fact: Untreated hypothyroidism in early pregnancy increases miscarriage, preterm birth and developmental risks — treatment is safer than waiting.
• Government note: Under the PMSMA (Pradhan Mantri Surakshit Matritva Abhiyan) scheme, a free thyroid function test is offered in the first trimester at government antenatal centres across India — a good entry point for anyone uninsured.