In brief — the direct answer
Thyroid hormones are essential for the healthy development of a baby’s brain and nervous system, particularly in the first trimester before the baby can produce their own hormones. If the mother’s thyroid is underactive (hypothyroidism) or overactive (hyperthyroidism), it can increase the risk of complications such as miscarriage, preterm birth, and subtle impacts on the child's future development. At the MFM Unit, we specialize in the delicate titration of thyroid medications to ensure you and your baby remain in the 'optimal zone.'
What is Thyroid Disorders in Pregnancy?
The thyroid is a small gland in the neck that acts like the body's 'control center' for metabolism.
- Hypothyroidism: The gland produces too little hormone. This is often caused by an autoimmune condition called Hashimoto’s.
- Hyperthyroidism: The gland produces too much hormone. This can be caused by Graves’ disease or sometimes by the high levels of pregnancy hormones (hCG) in the first trimester (temporary thyrotoxicosis).
Who is at risk?
You should have your thyroid checked early if you have:
- A known thyroid condition or family history.
- Symptoms like extreme fatigue, sensitivity to cold (hypo) or rapid heartbeat and unexplained weight loss (hyper).
- A history of Type 1 diabetes or other autoimmune conditions.
- A history of unexplained miscarriage or premature birth.
How we diagnose it
Thyroid status is determined by blood tests:
- TSH (Thyroid Stimulating Hormone): In pregnancy, we like the TSH to stay between 0.1 and 2.5 mIU/L in the first trimester.
- Free T4: Measuring the actual circulating thyroid hormone.
- Thyroid Antibodies: To check if the cause is an autoimmune reaction.
What does management involve?
Treatment is safe and highly effective:
- For Hypothyroidism: We use Levothyroxine, which is a synthetic version of the thyroid hormone you naturally lack. It is 100% safe for the baby. We typically increase the dose immediately after a positive pregnancy test.
- For Hyperthyroidism: We use medications like PTU (Propylthiouracil) in the first trimester and may switch to Methimazole later. These must be managed carefully by a specialist to protect the baby’s thyroid.
- Regular Monitoring: We check your blood every 4 to 6 weeks to adjust the dose as your pregnancy progresses.
What are the outcomes?
When well-controlled, thyroid disorders have no negative impact on the baby:
- Success: Babies born to mothers who maintain optimal TSH levels develop exactly like those born to mothers with normal thyroids.
- Postpartum: Many women need their thyroid dose decreased back to pre-pregnancy levels immediately after birth. Some women also experience 'Postpartum Thyroiditis,' a temporary inflammation of the gland after the baby is born.
When to see a subspecialist
If you have a pre-existing thyroid condition, you should seek a pre-pregnancy consultation or a referral as soon as you find out you are pregnant.
Led by Dr. Leanne Bricker, our maternal medicine service works alongside endocrinologists to provide seamless care. We ensure that your thyroid management is tailored to the specific physiological demands of each trimester, supporting your energy levels and your baby's future.
Questions to ask your doctor
References & Clinical Guidelines
- Guidelines for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum
- Thyroid Disease in Pregnancy (Practice Bulletin 223)
- Management of Thyroid Dysfunction during Pregnancy and Postpartum: Endocrine Society Clinical Practice Guideline