Thyroid hormones matter not only for getting pregnant but also for a healthy pregnancy and the baby’s normal development. That is why a thyroid check should start at the pregnancy planning stage.
Why is TSH checked when planning a pregnancy?
When planning a pregnancy, a gynaecological examination alone is not enough. Any type of thyroid dysfunction can make it harder to conceive, and untreated hormonal disorders can cause infertility in both women and men.
That is why it is advisable to see an endocrinologist before conceiving and, first of all, to have your TSH checked. Thyroid hormones must be tested especially if there have been recurrent miscarriages.
What changes in the thyroid during pregnancy?
In the first 12 weeks of pregnancy, the baby’s own thyroid gland is not yet fully formed, and the baby relies entirely on the mother’s hormones. For this reason, the mother’s thyroid has to work about 50% harder. Thyroid hormones play a key role in the development of the baby’s brain and nervous system.
In the first trimester, the rising hormone hCG is structurally very similar to TSH and stimulates the gland to produce extra hormone. As a result, the TSH level physiologically decreases. A slight enlargement of the gland during pregnancy is also natural, but it should not stop you from getting examined and making sure there is no disease.
The concept of a “normal” TSH also changes in pregnancy. Results are always assessed individually by the doctor, together with free T4. Reference ranges by trimester:
- 1st trimester: 0.1–2.5 mIU/L;
- 2nd trimester: 0.2–3.0 mIU/L;
- 3rd trimester: 0.3–3.0 mIU/L.
Why is hypothyroidism dangerous in pregnancy?
In pregnant women, thyroid hormone deficiency – hypothyroidism – is the most important and serious thyroid condition. Many thyroid diseases detected during pregnancy actually existed before: mild hypothyroidism can worsen under the influence of pregnancy, and a small nodule can grow.
If hormone deficiency is found in the mother in the first weeks of pregnancy, especially weeks 5–14, treatment should start immediately – this is the period when the baby’s brain develops fastest. Untreated hypothyroidism increases the risk of:
- miscarriage in the first trimester;
- pre-eclampsia and high blood pressure;
- preterm birth;
- delayed development in the baby and impaired development of the brain and nervous system.
What if TSH is low?
A TSH below normal in the first trimester is often a temporary condition related to hCG. However, it must be checked whether it is true hyperthyroidism, since hyperthyroidism can lead to miscarriage, preterm birth and low birth weight.
Radioactive iodine treatment is dangerous during pregnancy and is not used – treatment is carried out only with medication, under a doctor’s supervision.
How do iodine needs change?
During pregnancy, iodine loss in the urine increases and so does the need for iodine: a woman of reproductive age needs about 150 mcg a day, and a pregnant woman about 250 mcg. Iodine deficiency can lead to goitre in the mother and to serious developmental problems and neonatal hypothyroidism in the baby.
That is why it is important to use iodised salt in everyday meals. Take iodine supplements not on your own, but only after an endocrinologist’s examination and at the dose your doctor chooses.
Thyroid diseases should be treated and brought under control before pregnancy.
Dr. Samir Shukurov
Monitoring throughout pregnancy
If you have any thyroid condition, you should be monitored regularly by an endocrinologist throughout pregnancy – usually TSH and free T4 are checked every 4–6 weeks. Do not change the dose of your thyroid medication on your own: only the doctor makes the necessary adjustments.
This article is for general information only and does not replace a medical examination.