Introduction

Essential Thrombocythemia (ET) is a rare, long-term blood disorder in which the bone marrow produces too many platelets, cells that help your blood clot.¹ Normally, platelet counts are below 450,000 per microliter of blood, but in ET, they are usually much higher. ET belongs to a family of conditions known as myeloproliferative neoplasms, which also include polycythemia vera and myelofibrosis. Many people with ET have specific genetic mutations, such as JAK2, CALR, or MPL, that are associated with the onset of the disease.

Even though ET develops slowly, it still carries risks such as forming blood clots (which can cause stroke or heart attack), bleeding problems, or progression to more serious conditions like myelofibrosis or leukemia. Treatment depends on an individual’s risk level and may include aspirin or stronger medications.

It is important to know that ET carries additional risks during pregnancy.² These may include miscarriage, placental problems, or excessive bleeding.

If you or someone close to you is pregnant and has ET, this article will guide you through the challenges and help explain how the condition can be managed during pregnancy.

Symptoms of essential thrombocythemia

Due to the high platelet count, people with ET may develop blood clots that cause a variety of symptoms.

Often, people with ET are asymptomatic, meaning they don’t have any specific symptoms that clearly point to ET.³ 

When symptoms appear, they may include:⁴

• Fatigue (reported in up to 90% of patients)
• Insomnia, migraines, headaches, vision changes, and dizziness
• Thrombosis in different parts of the body, such as hepatic vein thrombosis, transient ischemic attacks (mini-strokes), or splenomegaly (enlarged spleen)
• Erythromelalgia (burning pain and redness in the hands or feet)
• Easy bruising

ET and pregnancy 

When you are pregnant, your body makes more blood to support your baby.⁵ This extra circulation puts added pressure on the blood vessels, which may cause them to become narrow. Along with natural hormonal changes, this increases the likelihood of developing a blood clot, which in turn increases the risk by about five times during pregnancy and shortly after delivery compared to women who are not pregnant.

Studies on pregnancy in women with ET show different outcomes, but the results are broadly similar:⁶

• The average live birth rate is about 60% (range 50-75%)
• First-trimester miscarriage is the most common complication (about 1/3 of pregnancies)
• Later complications (stillbirth, growth restriction, preeclampsia, or preterm delivery) are less common
• Women with very high platelet counts or previous complications face a higher risk of blood clots or, less commonly, bleeding problems
• Outcomes are improving with better care and treatments

Predictive factors for complications

Pregnancy outcomes in people with ET are not strongly predicted by past blood clots, bleeding history, or platelet counts alone. However, women who had complications in one pregnancy are more likely to face issues in subsequent ones, which is why the monitoring is crucial. 

Certain factors and underlying conditions may increase risk:

• Previous thrombosis
• Platelet count greater than 1500 × 10⁹/L (1.5 million/µL)
• Obesity⁷
• Cardiovascular risk factors (smoking, high blood pressure, high cholesterol)⁷ 
• JAK2 or MPL mutation, although the role of the gene mutation in pregnancy loss remains uncertain: some studies link it to a higher risk and increased platelet activation, others show no significant effect⁸ 
• Clotting disorders such as factor V Leiden or antiphospholipid syndrome⁹ 

Management strategies

ET is a chronic condition, so treatment for ET is aimed at preventing complications and relieving symptoms. It does not cure the disease or necessarily slow its progression.

Common treatments include:

• Aspirin
• Low molecular weight heparin (LMWH)
• Cytoreductive therapy (including hydroxyurea or anagrelide, which are usually avoided in pregnancy due to toxicity)
• Plateletpheresis, used only in emergencies to rapidly lower platelet counts during acute thrombosis or extreme thrombocytosis ¹⁰

Note that medications should always be prescribed and monitored by a doctor! 

Management depends on risk level:

• Very-low-risk patients: observation only; aspirin may be added if a patient has cardiovascular risks²
• Low-risk patients are typically treated with low-dose aspirin (once or twice daily). Cytoreductive drugs are avoided. If a patient has von Willebrand syndrome, aspirin should not be used due to increased bleeding risk
• Intermediate-risk patients: may require both aspirin and cytoreductive therapy, depending on symptoms, cardiovascular profile, underlying conditions and individual preferences
• High-risk patients: usually need both aspirin and cytoreductive therapy

How can one determine their risk level? The easy and convenient way is to use the IPSET thrombosis risk calculator to estimate the risk level and guide treatment.

Furthermore, lifestyle measures are recommended for all patients, including a healthy diet, exercise, weight management, and smoking cessation.

How can you help yourself? 

There is no specific lifestyle program for ET, but some general advice includes:

• Eating a balanced diet with enough fluids (6–8 glasses of water per day helps reduce dehydration-related risks)¹¹
• Staying physically active at a level appropriate for your condition may lower the risk of blood clots 
• Avoiding smoking and controlling other cardiovascular risk factors

Preconception and pregnancy Care

Planning

Women with ET should plan pregnancy carefully. This includes:

• Stopping drugs that could harm the baby
• Screening for clotting disorders (e.g., factor V Leiden, antiphospholipid antibodies)

During pregnancy

Pregnant patients with ET should be treated by a multidisciplinary team, including an obstetrician, hematologist, and anesthetist.

During pregnancy, regular monitoring of blood counts, blood pressure, and fetal growth is essential. Standard examination includes ultrasound and uterine artery Doppler (20–26 weeks) to check for placental problems. If there are any abnormalities, treatment may be changed. 

Summary

Most women with ET have a normal life expectancy. The main long-term risks are blood clots, bleeding, and, rarely, progression to leukemia or myelofibrosis. In pregnancy, the biggest risk is first-trimester miscarriage. If the pregnancy continues normally beyond this stage, serious maternal or obstetric complications are less common. The highest risk for blood clots is in the postpartum period, which requires careful monitoring and preventive treatment. With multidisciplinary care and regular monitoring, many women with ET can have safe and successful pregnancies.

Frequently Asked Questions (FAQs)

Can pregnancy be normal when Essential Thrombocythemia (ET) has been diagnosed?

Yes. The majority of women with ET have normal and healthy pregnancies. The main risk is early miscarriage, but after the first trimester, complications are less common.

Does ET shorten life expectancy?

No. Most people with ET live a normal life, though they might be at higher risk of blood clots, bleeding, or other complications.

What are the biggest pregnancy risks with ET?

The most frequent risk is miscarriage in the first trimester. Other risks include blood clots, bleeding, and placenta-related complications, especially postpartum.

Can stress and anxiety cause high platelets?

Some research suggests stress may increase platelet activity, but the evidence is not strong enough yet.¹²

Is aspirin safe to take during pregnancy?

Low-dose aspirin is usually safe for pregnant women with ET, especially for reducing clotting risk. However, treatment must be monitored by doctors.

What happens after delivery?

The postpartum period carries a higher risk of blood clots. Specific treatment may be recommended during this time. 

Can essential thrombocythemia go away?

No, ET is a chronic condition. The treatment can’t cure it, but it can prevent complications.