Thyroid Tests (TSH, FT4)
The thyroid is a small gland in the neck that produces hormones controlling the body's energy, growth and development. Thyroid tests measure thyroid-stimulating hormone (TSH), made by the pituitary gland to regulate the thyroid, and free thyroxine (FT4), the main thyroid hormone in the blood. Together they show whether the thyroid is underactive, overactive or normal.
At YGOPH, thyroid tests are requested for women with irregular periods, difficulty conceiving or a goitre, during pregnancy when there are symptoms or a history of thyroid disease, and for children with slow growth or delayed development. Normal thyroid function in the mother is important for the development of the baby's brain.
What do TSH and FT4 show?
TSH is the best first test. When the thyroid is underactive (hypothyroidism), TSH rises as the pituitary tries to stimulate it; when the thyroid is overactive (hyperthyroidism), TSH falls. FT4 confirms the diagnosis and shows how severe the problem is. Some patients also need FT3 or thyroid antibodies. Your doctor interprets the results using reference values adapted to pregnancy or to your child's age.
- Tiredness, weight changes, feeling unusually cold or hot, palpitations
- Irregular periods or difficulty getting pregnant
- A swelling in the neck (goitre) or a thyroid nodule
- Pregnancy in women with a history of thyroid disease
- Children with slow growth, delayed development or prolonged newborn jaundice
- Monitoring thyroid treatment
Good to know
Thyroid and pregnancy
Pregnancy changes thyroid hormone levels, especially in the first trimester, so doctors use pregnancy-specific reference ranges. An untreated underactive thyroid can increase the risk of miscarriage and affect the baby's development, while severe nausea and vomiting in early pregnancy can temporarily change thyroid results. Women already on treatment often need a dose adjustment as soon as pregnancy is confirmed.
Thyroid problems in children
A baby born with an underactive thyroid may look normal at first but show prolonged jaundice, constipation, poor feeding or a large tongue. Early treatment prevents serious developmental delay, so doctors test quickly when there is any doubt. In older children, thyroid problems can slow growth and affect school performance.