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Thyroid nodules in pregnancy

Thyroid FNAC — During Pregnancy

Finding a thyroid nodule in pregnancy raises questions your obstetrician may not have time to answer fully. This page addresses the three that matter most: whether the biopsy is safe, whether it can wait, and what changes if the result comes back abnormal.

Medically reviewed by Dr. Muralidhar Muddusetty, Surgical Oncologist, MBBS (AIIMS) · MS Surgery (AIIMS) · DNB Surg Onc · MRCS (Edinburgh) · Last reviewed September 2026

  • Safe, with no radiation — FNAC uses a thin needle and ultrasound guidance. There is no radiation and no general anaesthesia.
  • Often deferrable — Most nodules found in pregnancy are monitored with ultrasound rather than biopsied immediately.
  • Results use the same Bethesda system — The six-category reporting system is the same as outside pregnancy. Your team interprets it in the context of your stage of pregnancy.
  • Surgery timing changes — If surgery is needed, it is usually planned after delivery or, in specific circumstances, in the second trimester.
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Thyroid FNAC is safe during pregnancy — the needle is thin, ultrasound-guided, and involves no radiation or general anaesthesia. Most nodules are monitored with ultrasound rather than biopsied immediately. If your result is suspicious, surgery decisions follow a different timeline in pregnancy.

What do the terms on your referral mean?

FNAC (Fine Needle Aspiration Cytology)
A biopsy done with a very thin needle to collect a few cells from the nodule. No cuts, no stitches, no general anaesthesia.
Thyroid nodule
A lump or growth within the thyroid gland. Most are benign. Pregnancy can make them slightly more prominent on ultrasound.
Bethesda category
A six-level system used to report FNAC results, from Bethesda I (non-diagnostic) to Bethesda VI (malignant). Each level carries an estimated risk range for cancer, as published in the Bethesda System for Reporting Thyroid Cytopathology.
TSH (Thyroid Stimulating Hormone)
A blood test that shows how active your thyroid is. TSH falls naturally in the first trimester. Your team uses pregnancy-specific reference ranges to interpret your result, not the standard ranges on the lab printout.

What happens during a thyroid FNAC?

  1. Positioning

    You lie on your back with your neck extended slightly. A pillow under your shoulders helps the thyroid become accessible.

  2. Ultrasound guidance

    The doctor uses an ultrasound probe to locate the nodule precisely and guide the needle into it.

  3. The needle pass

    A thin needle is inserted through the skin into the nodule. Most people feel mild pressure. The procedure takes a few minutes.

  4. Sample collection

    Two to four passes are usually made to collect enough cells. Each pass takes a few seconds.

  5. Dressing and discharge

    A small cotton pad is applied. You can return to your usual activities the same day.

  6. Results

    The sample is examined by a pathologist and reported using the Bethesda classification. Results typically take five to seven days.

Which signs mean the biopsy should not wait?

  • The nodule has grown noticeably within a few weeks
  • Your voice has become hoarse or your swallowing has changed
  • Neck lymph nodes feel enlarged or firm alongside the nodule
  • Ultrasound shows features your doctor has described as high-risk
  • Your doctor has told you the nodule is large
  • You have a personal or close family history of thyroid cancer

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Can the biopsy or surgery wait until after you deliver?

For most nodules found in pregnancy, yes. If ultrasound features are reassuring and the FNAC result is benign or low-risk, active monitoring with scans is safe until after delivery.

If the FNAC result is in a concerning category, surgery is still usually deferred to the postpartum period. ATA guidance supports this approach for most differentiated thyroid cancers found before mid-pregnancy, because these cancers tend to grow slowly.

When surgery cannot wait — because of rapid growth or pressure on nearby structures — the second trimester is considered the safest window for the operation.

How does pregnancy change the way a thyroid nodule is managed?

Radioactive iodine is contraindicated throughout pregnancy and breastfeeding. If it is part of your eventual treatment plan, it will be deferred well beyond delivery.

Thyroid hormone levels change naturally during pregnancy. Your team will interpret your blood results against pregnancy-specific reference ranges, not the standard ranges printed on the lab report.

Ultrasound monitoring is used more frequently in pregnancy to watch nodules rather than proceeding to biopsy or surgery. This means more scans, but fewer procedures — a deliberate and evidence-based approach.

What else should you know if a nodule was found during your pregnancy?

Could the FNAC harm the baby?

No. The needle goes into the neck only, well away from the uterus. Ultrasound guidance directs it precisely into the nodule. There is no radiation, no sedation, and no general anaesthesia — each of which carries small but real risks in pregnancy. ATA and ESMO guidance supports FNAC at any stage of pregnancy when there is a clinical reason to perform it.

I was told to wait — what should I watch for in the meantime?

Watch for any change in the size of the lump that you can feel, hoarseness in your voice, or difficulty swallowing. Mention the nodule to your obstetrician at every antenatal appointment so it stays in view across both teams. If anything changes before your next scheduled scan, contact your team rather than waiting for the appointment.

Will I need surgery before I deliver?

Most people do not. Surgery for a thyroid nodule found in pregnancy is usually deferred to the postpartum period. If surgery cannot be deferred — because the nodule is growing rapidly, compressing nearby structures, or the biopsy result is strongly suspicious — the second trimester is considered the safest window. This decision is made jointly by your oncologist and obstetrician.

Can I breastfeed while being treated for thyroid cancer?

If your treatment involves thyroid hormone tablets alone, breastfeeding is generally compatible with treatment. If radioactive iodine is part of your plan, breastfeeding must stop before treatment and cannot be resumed afterwards, because radioactive iodine passes into breast milk. Your team will plan the timing carefully and give you a clear picture before you make any decisions about feeding.

My FNAC came back as Bethesda III or IV — what does that mean in pregnancy?

Bethesda III and IV results are indeterminate — neither clearly benign nor clearly malignant. In pregnancy, many teams recommend monitoring closely with ultrasound or repeating the FNAC rather than proceeding immediately to surgery, because a proportion of indeterminate results turn out to be benign at final pathology. Where molecular testing on the sample is available, it may help clarify the risk. Your oncologist and obstetrician will decide together on the right next step.

Will the stress of this affect my pregnancy?

Finding a thyroid nodule in pregnancy is frightening, and feeling anxious is a reasonable response. The nodule itself is unlikely to affect the pregnancy. What your team will watch carefully is your thyroid hormone level, because low or high thyroid hormone can affect fetal development. This is monitored with a blood test and is treatable safely in pregnancy. Tell your obstetrician how you are feeling so that appropriate support is available to you.

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Common questions

Frequently asked questions

Is thyroid FNAC safe during pregnancy?

Yes. FNAC is safe throughout pregnancy. The needle enters the neck only, guided precisely by ultrasound. There is no radiation and no general anaesthesia. ATA and ESMO guidance both support its use when there is a clinical reason to perform it. The procedure takes a few minutes and you can return to your usual activities the same day. Being pregnant does not change the technique or the safety of the procedure itself.

Can a thyroid nodule grow during pregnancy?

Some nodules do grow slightly during pregnancy, driven by hormonal changes and increased blood flow to the thyroid. Growth alone does not mean the nodule has become dangerous. Your team watches for growth that is rapid, occurs alongside new symptoms, or appears on ultrasound with additional concerning features. If a nodule that was stable changes noticeably before your next scheduled scan, contact your team rather than waiting.

What does a Bethesda III or IV result mean for the pregnancy?

Bethesda III and IV are indeterminate results — not clearly benign and not clearly malignant. In pregnancy, most teams recommend close ultrasound monitoring and sometimes a repeat FNAC rather than immediate surgery, because a proportion of these results are benign at final pathology. The decision depends on which Bethesda category you are in, how the nodule looks on ultrasound, and your stage of pregnancy. Your oncologist and obstetrician will assess this together.

If I need thyroid surgery, will it affect the baby?

Thyroid surgery in the second trimester has a good safety record. If surgery is planned for after delivery, the wait is usually safe because most thyroid cancers found in pregnancy grow slowly — a position supported by ATA guidance for most differentiated thyroid cancers. Whether to operate before or after delivery depends on the biopsy result, the behaviour of the nodule, and your stage of pregnancy. Your surgical team and obstetrician make this decision together.

Should I tell my obstetrician about the thyroid nodule?

Yes, immediately if you have not already. Your obstetrician needs to know about the nodule, any biopsy results, and your thyroid blood test results, because thyroid function affects fetal development. They also need to be part of any decision about surgery timing. In most cases your oncologist and obstetrician will communicate directly — but confirm that both teams are aware of each other's plans rather than assuming.

Will I need radioactive iodine treatment?

Not during pregnancy or breastfeeding — radioactive iodine is contraindicated in both. If it is part of the standard treatment for your diagnosis, your team will defer it until well after delivery and after breastfeeding is complete. ATA guidance supports deferring the full treatment plan for most differentiated thyroid cancers found in pregnancy, but your team will confirm this based on your specific situation and biopsy result.

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