Creator: Dr. Devang Patel
Published: 2026-09-22

Thyroid disorders are among the most common medical conditions in pregnancy, and studies from India show that a significant number of pregnant women have an underactive thyroid (hypothyroidism), many without knowing it. The thyroid hormone matters especially in early pregnancy, because the baby depends completely on the mother’s supply for the first 12 weeks while its own brain and nervous system are forming. The good news is that thyroid problems are simple to detect with a blood test and straightforward to treat with medicines that are safe in pregnancy.

Why the thyroid matters in pregnancy

Pregnancy hormones increase the body’s demand for thyroid hormone by roughly a quarter to a half. A healthy thyroid adjusts. When the thyroid cannot keep up, or when a woman already has hypothyroidism, the level can drop. Untreated or poorly controlled hypothyroidism is linked to miscarriage, anaemia, high blood pressure, preterm birth, low birth weight and, in severe cases, effects on the baby’s neurological development. An overactive thyroid, if uncontrolled, has its own risks, including high blood pressure, fast heart rate and growth problems in the baby.

Understanding your TSH report

TSH (thyroid stimulating hormone) is the main screening test. It works in reverse: a high TSH means the thyroid is underactive, and a low TSH means it may be overactive. Reference ranges in pregnancy are lower than outside pregnancy, especially in the first trimester.

Ideally, laboratories use their own trimester-specific ranges for pregnant women
Where these are not available, the American Thyroid Association suggests an upper limit of about 4.0 mIU/L, with lower values expected in the first trimester
Many clinicians in India aim to keep TSH below about 2.5 mIU/L in the first trimester and below about 3.0 mIU/L later in pregnancy for women on treatment
Free T4 shows how much active hormone is available, and TPO antibodies show whether the thyroid is affected by an autoimmune process
A mildly low TSH in the first trimester is often a normal effect of the pregnancy hormone hCG, especially with severe vomiting or twins

Your doctor interprets the result with your free T4, antibodies, history and the week of pregnancy. A single borderline value is not a diagnosis by itself.

Women with a newly raised TSH in pregnancy are usually started on a low dose of levothyroxine, particularly if TPO antibodies are positive or the value is clearly above the range. Treatment of mildly raised TSH with negative antibodies is decided case by case. Symptoms of an underactive thyroid - tiredness, weight gain, constipation, feeling cold, dry skin - overlap with ordinary pregnancy symptoms, which is why a blood test is more reliable than how you feel.

If you already take thyroxine

Check TSH before trying to conceive, and plan pregnancy when it is well controlled
As soon as your pregnancy test is positive, contact your doctor - the dose usually needs to be increased by about 20 to 30 percent
TSH is checked about every four weeks until mid-pregnancy, and at least once around 30 weeks
After delivery, the dose usually goes back to your pre-pregnancy level, with a check about six weeks later

Do not stop your thyroxine tablet when you find out you are pregnant. It is safe for the baby, and stopping it is one of the most common avoidable causes of poor thyroid control in early pregnancy.

How to take thyroxine correctly

Small habits make a large difference to how well levothyroxine is absorbed, and many “dose not working” problems turn out to be timing problems.

Take it on an empty stomach first thing in the morning, with plain water
Wait 30 to 60 minutes before tea, coffee, milk or breakfast
Keep at least four hours between thyroxine and iron or calcium tablets - take those later in the day
Antacids and soya products can also reduce absorption; space them apart
Take it at the same time every day; if you miss a dose, take it when you remember, and you can take two the next day if a whole day is missed
Do not switch brands without telling your doctor, as a recheck may be needed

Overactive thyroid in pregnancy

Hyperthyroidism is less common. The most frequent cause in early pregnancy is a temporary rise linked to hCG, which usually needs no treatment. Graves’ disease, an autoimmune condition, does need treatment, with medicines chosen carefully for each stage of pregnancy - propylthiouracil is usually preferred in the first trimester, and carbimazole or methimazole later. Women with Graves’ disease, current or treated in the past, also need a check of antibodies that can cross the placenta, and the baby’s heart rate and growth are monitored.

After the baby is born

The newborn has a routine thyroid screening test, usually a heel-prick blood sample in the first days
Some women develop postpartum thyroiditis, a temporary thyroid inflammation in the first year after delivery, which can cause tiredness, palpitations or low mood
Thyroxine and the usual anti-thyroid medicines are compatible with breastfeeding
Women with TPO antibodies have a higher chance of developing hypothyroidism later, so a yearly TSH test is sensible

Use iodised salt at home. Iodine is essential for thyroid hormone, and pregnancy and breastfeeding increase the need for it. Avoid taking separate iodine or kelp supplements unless prescribed.

When to see a doctor

Have your TSH checked before pregnancy if possible, and at your first antenatal visit. Contact your doctor straight away when your pregnancy test is positive if you already take thyroxine, or if you notice palpitations, tremor, marked weight loss, extreme tiredness or a swelling in the neck. At Divine Women’s Hospital, Gota, Dr. Devang Patel reviews thyroid results alongside the rest of your antenatal care and adjusts the dose at each stage of pregnancy.

More patient guides

This guide is general information for patients and does not replace a consultation with your own doctor.

Thyroid in pregnancy: normal TSH levels and how treatment changes