Why you should have your thyroid checked in pregnancy

Despite the fact that there is now substantial evidence that thyroid deficiency during pregnancy can result in many problems in the newborn baby, there is no national programme to screen for thyroid disease in pregnancy. That is why it is important that mums-to-be should consider having thyroid function tests done in pregnancy.

Hypothyroidism – risks of pregnancy complications:

Hypothyroidism increases the risk of pregnancy complications such as miscarriage, preterm birth, still birth, pre-eclampsia, placental abruption, postpartum haemorrhage and premature delivery. [1]

The presence of positive thyroid antibodies doubles the risk of miscarriage and preterm delivery [2], and increases the risk of stillbirth and other conditions. Worryingly, thyroid autoantibodies can be positive in 12-15% of reproductive age women, particularly if they are older when first pregnant.

Hypothyroidism – risks to mum

Untreated, or inadequately treated, hypothyroidism has been associated with maternal anaemia (low red blood cell count), myopathy (muscle pain, weakness), congestive heart failure, pre-eclampsia, placental abnormalities, low birth weight infants and postpartum haemorrhage (bleeding).

Hypothyroidism – risks to baby

In the early part of pregnancy the developing foetus is entirely dependent on the mother’s thyroid hormone, so it is vitally important that the pregnant woman’s thyroid hormone levels are adequate.

If the thyroid stimulating hormone (which comes from the brain and kicks the thyroid gland to produce thyroid hormone) is having to work in overdrive to get the thyroid gland to produce enough thyroid hormone, this can result in deficits in the intellectual development of infants. [3] Studies have shown that with a raised thyroid stimulating hormone, the foetus is at risk of a lower IQ measured as -7 points between the ages of 7 and 9! [4], Other risks to the foetus are being small for dates or being born prematurely.

So the thyroid stimulating hormone, or TSH, should be checked when thinking about getting pregnant and when pregnant.[5] [6]This is especially true in women at high risk for thyroid disease, such as those who have had prior treatment for thyroid disease, a positive family history of thyroid disease, patients with type 1 diabetes and any woman with symptoms suggestive of thyroid disease.  All women thinking of getting pregnant, or pregnant with a raised TSH should be treated and those with significantly raised thyroid autoantibodies should consider treatment, since thyroxine therapy reduced miscarriage rate by 52% and preterm delivery by 69%.[7]

Treatment during pregnancy

What about if you already have hypothyroidism and fall pregnant? Hypothyroid women on treatment should have their TSH level checked as soon as they find out they are pregnant as its likely they will need to increase their dose of T4 by a small amount (25 or 50 mcg/day).[8]

Throughout the pregnancy they will require much closer monitoring of their thyroid function – 6 weekly thyroid blood tests. After the birth the TSH should be checked (e.g. at 2 to 4 weeks post-birth), at which time the dose of thyroxine can usually be reduced back to the pre-pregnancy level. It is important to check the thyroid after birth as thyroiditis (inflammation of the thyroid gland) occurs in 5-9% of the population within 2 to 6 months after birth and can give rise to transient thyroid dysfunction. The presence of thyroid autoantibodies in early pregnancy predicts a 30 – 50% chance of postpartum thyroiditis developing.


All too often, thyroid problems are diagnosed too late. Mums-to-be should get a comprehensive thyroid profile measured. Pregnancy is an opportune time for making an early diagnosis and early detection of problems can only benefit you, your pregnancy, and your unborn child.


[1]Overt and subclinical hypothyroidism complicating pregnancy. 

[2] Association between thyroid autoantibodies and miscarriage and preterm birth: meta-analysis of evidence

[3] American Thyroid Association Statement on Early Maternal Thyroidal Insufficiency: Recognition, Clinical Management and Research Directions

[4] Maternal Thyroid Deficiency during Pregnancy and Subsequent Neuropsychological Development of the Child

[5] Should all pregnant women be screened for hypothyroidism?

[6] Screening for thyroid disease in pregnancy.

[7] Association between thyroid autoantibodies and miscarriage and preterm birth: meta-analysis of evidence

[8] Maternal hypothyroidism: recognition and management.