Thyroid Disorders in pregnancy– A Practical Guide for Patients
When Should You See an Endocrinologist?
Consult an endocrinologist if you:
- Are planning pregnancy and have thyroid disease
- Become pregnant while taking thyroid medication
- Have abnormal thyroid blood tests
- Experience symptoms of thyroid dysfunction
- Have recurrent miscarriages
- Have infertility associated with thyroid disease
- Develop thyroid swelling during pregnancy
Thyroid Disorders in Pregnancy
Normal thyroid function is essential for fertility, a healthy pregnancy, and fetal brain development. Thyroid disorders should be identified early and managed throughout pregnancy.
Why Thyroid Health Matters During Pregnancy
The thyroid gland produces hormones that are essential for:
- Baby’s brain development
- Nervous system development
- Normal fetal growth
- Healthy placenta
- Maternal metabolism
- Maintaining a healthy pregnancy
Untreated thyroid disease increases the risk of pregnancy complications and may affect both mother and baby.
Hypothyroidism During Pregnancy
What is Hypothyroidism?
Hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormone.
During pregnancy, diagnosis is based on elevated TSH levels using pregnancy-specific reference ranges.
Common Causes
The most common causes include:
- Hashimoto’s thyroiditis
- Previous thyroid surgery
- Previous radioactive iodine treatment
- Previous postpartum thyroiditis
- Pituitary disorders
Symptoms
Some women experience:
- Persistent tiredness
- Excessive sleepiness
- Weight gain
- Constipation
- Dry skin and hair fall
- Feeling unusually cold
- Depression
- Slow heart rate
Because many symptoms overlap with normal pregnancy, blood tests are essential.
Who Should Be Screened?
Women at higher risk include those with:
- Previous thyroid disease
- Family history of thyroid disease
- Goitre
- Type 1 diabetes
- Other autoimmune diseases
- Infertility
- Recurrent miscarriage
- Previous preterm birth
- Previous neck radiation
Risks of Untreated Hypothyroidism
Without treatment, hypothyroidism may increase the risk of:
- Miscarriage
- High blood pressure during pregnancy
- Preeclampsia
- Premature delivery
- Low birth weight
- Stillbirth
- Postpartum haemorrhage
- Impaired brain development in the baby
Treatment
Levothyroxine is the treatment of choice.
Women already taking thyroid medication often require a higher dose soon after pregnancy begins.
Regular thyroid function tests are performed every 4 weeks during the first half of pregnancy and periodically thereafter to keep thyroid hormone levels within the recommended pregnancy range.
Treatment of Hypothyroidism in pregnancy
| Situation | Recommendation | Monitoring |
| Known hypothyroidism before pregnancy | Increase levothyroxine promptly (often by about 20–30% or two extra tablets/week) after confirming pregnancy, then review with clinician. | TSH every ~4 weeks until stable, then at least once each trimester. |
| Newly diagnosed overt hypothyroidism | Start levothyroxine without delay. | Adjust dose to achieve trimester-appropriate TSH. |
| Subclinical hypothyroidism | Treat according to TSH level, thyroid antibody status and guideline recommendations. | Repeat TSH after dose adjustments. |
How to Take Levothyroxine
- Take on an empty stomach with water.
- Take 30–60 minutes before breakfast or at bedtime (3–4 hours after food).
- Separate iron, calcium and prenatal vitamins by at least 4 hours.
- Do not stop levothyroxine without medical advice.
Table. Medicines in Pregnancy
| Medicine | Use | Key Advice |
| Levothyroxine | Hypothyroidism | Take on an empty stomach; separate iron/calcium by at least 4 hours. |
| Propylthiouracil (PTU) | Preferred in the 1st trimester for Graves’ disease when antithyroid therapy is required | Use the lowest effective dose. |
| Methimazole/Carbimazole | Usually preferred after the 1st trimester if ongoing treatment is needed | Monitor thyroid function regularly. |
Treatment Goals for Hypothyroidism During Pregnancy
The primary goal of treatment is to maintain thyroid hormone levels within the pregnancy-specific target range to support maternal health and healthy fetal development.
Target TSH Levels
The aim is to keep TSH in the lower half of the trimester-specific reference range:
| Pregnancy Stage | Target TSH |
| First trimester | 0.1–2.5 mIU/L |
| Second trimester | 0.2–3.0 mIU/L |
| Third trimester | 0.3–3.0 mIU/L |
Thyroid function should be monitored regularly throughout pregnancy, and the dose of levothyroxine adjusted as needed to maintain these targets.
Treatment Goals for Graves’ Disease During Pregnancy
The objective is to achieve good control of maternal hyperthyroidism while avoiding excessive treatment that could affect the developing baby.
Treatment aims include:
- Use the lowest effective dose of antithyroid medication.
- Maintain free T4 (FT4) at or just above the upper limit of the trimester-specific reference range.
- Keep maternal thyroid hormone levels controlled while minimizing fetal exposure to medication.
- Assess thyroid function at least once every month and adjust medication according to laboratory results.
- TSH often remains suppressed throughout pregnancy and should not be used alone to guide treatment adjustments. Free T4 is the preferred marker for monitoring therapy.
Frequently Asked Questions
| Question | Answer |
| Can thyroid disease affect my baby? | Untreated thyroid disease can increase maternal and fetal risks, but appropriate treatment greatly improves outcomes. |
| Should I continue levothyroxine during pregnancy? | Yes. Do not stop it without medical advice. |
| Can I breastfeed while taking thyroid medicine? | Levothyroxine is compatible with breastfeeding. Antithyroid medicines can often be used in appropriate doses under medical supervision. |
| How often should thyroid tests be checked? | Your doctor will individualize testing; many women with treated hypothyroidism require frequent checks early in pregnancy. |
| Can I breastfeed while taking levothyroxine? | Yes. Levothyroxine is compatible with breastfeeding. |
| How often should thyroid tests be checked? | Usually, every 4 weeks after dose changes until stable, then periodically throughout pregnancy. |
Key Messages
- Plan pregnancy with well-controlled thyroid function.
- Increase levothyroxine promptly after pregnancy confirmation under medical guidance.
- Attend scheduled thyroid blood tests.
- Early treatment protects both mother and baby.
Hyperthyroidism During Pregnancy
What is Hyperthyroidism?
Hyperthyroidism occurs when the thyroid gland produces excessive thyroid hormone.
The most common cause is Graves’ disease, although temporary gestational thyrotoxicosis may also occur during early pregnancy.
Symptoms
Common symptoms include:
- Palpitations
- Tremor
- Weight loss despite normal eating
- Heat intolerance
- Anxiety
- Excessive sweating
- Fast heartbeat
Diagnosis
Diagnosis usually involves:
- TSH
- Free T4
- Total T3
- Thyroid antibody testing (TRAb)
- Ultrasound when appropriate
Thyroid scans using radioactive iodine are not performed during pregnancy.
Treatment
Treatment depends on the cause.
Options may include:
- Careful observation
- Antithyroid medications
- Beta-blockers for short-term symptom control
- Surgery in selected cases during the second trimester
Treatment aims to maintain maternal thyroid hormone levels within the safe pregnancy range while minimizing fetal risks.
Gestational Transient Thyrotoxicosis (GTT)
Include:
- Why it occurs (high hCG levels stimulating the thyroid)
- Association with severe morning sickness (hyperemesis gravidarum)
- Increased frequency in twin pregnancies
- Usually temporary
- Antithyroid medication is generally not required
This is valuable information for pregnant women because GTT is commonly confused with Graves’ disease
Postpartum Thyroiditis
Some women develop thyroid dysfunction after delivery.
The condition may begin with temporary hyperthyroidism followed by hypothyroidism before returning to normal.
Women with thyroid antibodies during pregnancy have a higher risk and should undergo follow-up thyroid function testing after childbirth.
Thyroid Nodules During Pregnancy
Finding a thyroid lump during pregnancy does not necessarily indicate cancer.
Evaluation usually includes:
- Clinical examination
- Thyroid function tests
- Thyroid ultrasound
- Fine-needle aspiration biopsy when indicated
Ultrasound-guided biopsy is safe during pregnancy when clinically necessary.
Practical Advice for Patients
- Do not stop thyroid medication after becoming pregnant without consulting your endocrinologist.
- Attend regular thyroid function testing throughout pregnancy.
- Inform your doctor if you are taking biotin supplements, as they can interfere with thyroid blood test results.
- Plan thyroid evaluation before pregnancy if you have known thyroid disease.
- Continue follow-up after delivery because thyroid dysfunction may develop postpartum.
References
- American Thyroid Association. Guidelines for the Diagnosis and Management of Thyroid Disease During Pregnancy and Postpartum.
- Endocrine Society Clinical Practice Guideline on Thyroid Disease in Pregnancy.
- European Thyroid Association Guidelines.