Why does underactive thyroid in pregnancy cause tiredness in pregnancy?

The thyroid makes hormones that help regulate how the body uses energy. With hypothyroidism, hormone levels may be too low for the body's needs. This can make ordinary activities feel unusually draining and may cause a heavy, slowed-down feeling, reduced concentration, feeling cold, constipation, dry skin, or muscle aches.

Pregnancy itself commonly changes sleep, circulation, appetite, and energy demands, so tiredness can have several causes at once. Fatigue alone cannot identify a thyroid problem. Most people with Underactive Thyroid in Pregnancy notice tiredness in pregnancy, but the symptom can also occur without hypothyroidism.

A clinician may assess your symptoms alongside thyroid blood tests, commonly including thyroid-stimulating hormone and free thyroxine. The results are interpreted in the context of pregnancy and your medical history rather than from tiredness alone.

Tell your maternity team or doctor if tiredness is persistent, worsening, or interfering with daily activities. Mention other changes such as feeling cold, constipation, skin or hair changes, low mood, or difficulty concentrating. They can decide whether thyroid testing or another evaluation is appropriate.

If you already take thyroid replacement medicine, take it exactly as prescribed and do not change the dose or stop it on your own. Pregnancy can alter thyroid hormone needs, so keep planned blood-test appointments and tell your clinician about vitamins, iron, or calcium supplements because these may affect how the medicine is absorbed when taken close together.

Support your energy with regular food and fluids, gentle activity if it feels comfortable, and rest. These measures may ease fatigue, but they do not replace assessment when symptoms are new or difficult to manage.

Contact your maternity team promptly if severe or rapidly worsening tiredness comes with fainting, breathlessness at rest, chest pain, a racing or irregular heartbeat, confusion, marked weakness, or an inability to keep fluids down. These symptoms can have causes that need urgent assessment and should not be attributed to the thyroid without an examination.

Seek advice soon if tiredness is affecting your ability to work, care for yourself, eat, sleep, or attend appointments. A clinician can check for thyroid imbalance and other pregnancy-related causes, including anaemia, infection, sleep problems, or mood symptoms.

You could ask: Could my symptoms be related to thyroid function or another pregnancy-related cause? Which thyroid tests are suitable for me, and when should they be repeated? If I take thyroid replacement, should the timing change around my prenatal vitamins? Which symptoms should prompt an urgent call?