Blood Clots in the Placenta During Pregnancy

When you’re pregnant, the placenta serves as your baby’s lifeline, delivering oxygen and nutrients while removing waste. But when blood clots form in the placenta, this vital connection can be disrupted, potentially leading to serious complications. Understanding placental blood clots can help you recognize warning signs and work with your healthcare team to protect your baby’s health.

What Are Placental Blood Clots and Why Do They Form?

Placental blood clots, medically known as placental thrombosis, intervillous thrombohematoma, or thrombotic vasculopathy, are clots that develop within the blood vessels of the placenta, in the spaces between placental tissue, or in the umbilical cord. These clots can form on either the maternal side (where your blood flows) or the fetal side (where your baby’s blood circulates).

When these clots are large or numerous, they block the normal exchange of oxygen and nutrients between you and your baby. This disruption can lead to placental insufficiency, a condition where the placenta can no longer adequately support your baby’s growth and development.

How Common Are Blood Clots in the Placenta?

While venous thromboembolism (blood clots in veins) affects about 1 to 2 out of every 1,000 pregnancies overall, the risk increases significantly for women with certain health conditions. Placental abruption, which often involves acute blood clot formation and separation of the placenta from the uterine wall, occurs in approximately 1% of all pregnancies.

In cases of stillbirth, fetal thrombotic vasculopathy is identified in 2% to 5% of cases, highlighting its role in the most severe pregnancy outcomes. These clots have also been linked to cerebral palsy and neonatal stroke in surviving infants.

What Puts You at Higher Risk for Placental Blood Clots?

Several factors can increase your risk of developing blood clots in the placenta during pregnancy:

Blood Clotting Disorders

Women with hereditary or acquired thrombophilia (conditions that make blood clot more easily) face significantly higher risks. These include:

• Factor V Leiden mutation
• Prothrombin gene mutation
• Antiphospholipid syndrome
• Protein C or S deficiency

Medical Conditions

Certain chronic health conditions contribute to hypercoagulability (increased clotting tendency) and impaired placental blood flow:

• High blood pressure (hypertension)
• Diabetes
• Obesity
• Pre-existing cardiovascular disease
• Kidney disease
• Autoimmune disorders

Age and Lifestyle Factors

• Maternal age 35 or older
• Smoking, which damages placental blood vessels
• Multiple pregnancy (twins, triplets, or more)

Recent COVID-19 Infection

Recent studies have shown that COVID-19 infection during pregnancy increases the risk of placental thrombosis and fetal growth restriction, even when the infection resolves before delivery. This has emerged as a significant risk factor that doctors now monitor closely.

What Are the Warning Signs of Placental Blood Clots?

Some cases of placental blood clots cause no symptoms and are only discovered during ultrasound examinations or after delivery. However, you should contact your healthcare provider immediately if you experience:

• Decreased fetal movement or changes in your baby’s normal movement patterns
• Vaginal bleeding
• Severe or persistent abdominal pain
• Cramping or contractions before 37 weeks
• Sudden severe back pain

These symptoms can indicate placental abruption or other serious complications requiring immediate medical attention.

How Are Placental Blood Clots Diagnosed?

Your healthcare provider may use several methods to detect or evaluate placental blood clots:

During Pregnancy

Ultrasound imaging is the primary tool for identifying placental abnormalities during pregnancy. In some cases, MRI may provide additional detailed information about placental structure and blood flow. Doppler ultrasound can assess blood flow through the umbilical cord and placental vessels.

Growth restriction identified on routine ultrasound measurements may prompt further investigation for placental problems, including blood clots.

After Delivery

In many cases, placental blood clots are definitively diagnosed through histopathological examination (microscopic study) of the placenta after birth. This is particularly important when there have been complications during pregnancy or delivery, as it helps explain what went wrong and guides future pregnancy management.

What Complications Can Placental Blood Clots Cause?

The effects of placental blood clots depend on their size, number, and location. Complications can affect both you and your baby.

Effects on Your Baby

• Fetal growth restriction: Up to 25% of babies affected by placental clots experience slower than normal growth
• Preterm birth: Approximately 25% of affected pregnancies result in early delivery
• Low birth weight: Inadequate nutrient transfer leads to smaller babies
• NICU admission: About 13% to 15% of affected babies require intensive care after birth
• Stillbirth: In severe cases, extensive clotting can lead to pregnancy loss
• Neurological injury: Chronic oxygen deprivation can result in cerebral palsy or neonatal stroke

Effects on You

Placental abruption, often caused by acute blood clot formation, can cause severe maternal hemorrhage and requires emergency delivery. This complication carries risks of significant blood loss, need for blood transfusion, and rarely, hysterectomy.

Can Placental Blood Clots Be Prevented?

While not all cases can be prevented, several strategies can reduce your risk:

Before Pregnancy

If you have known risk factors like clotting disorders, previous blood clots, or chronic medical conditions, work with a maternal-fetal medicine specialist to develop a management plan before conceiving. This planning allows for optimization of your health and appropriate preventive measures from the start of pregnancy.

During Pregnancy

Your healthcare provider may recommend:

• Low-molecular-weight heparin injections for women with significant clotting risk
• Low-dose aspirin (typically started before 16 weeks of pregnancy in high-risk women)
• More frequent prenatal visits and ultrasound monitoring
• Careful management of blood pressure and blood sugar levels
• Smoking cessation support

Healthy Pregnancy Practices

Supporting your overall health benefits placental function:

• Attend all scheduled prenatal appointments
• Follow your provider’s recommendations for managing chronic conditions
• Maintain a balanced, nutritious diet
• Stay physically active as recommended by your provider
• Avoid smoking and secondhand smoke exposure

What Treatment Options Are Available?

If placental blood clots are detected during pregnancy, treatment focuses on monitoring your baby’s wellbeing and managing complications:

Increased Monitoring

You’ll likely need more frequent prenatal visits and additional ultrasounds to track fetal growth and amniotic fluid levels. Non-stress tests may be used to assess your baby’s heart rate patterns and overall condition.

Medication

Depending on your situation, your doctor may prescribe anticoagulation therapy (blood thinners) to prevent additional clot formation. However, this decision requires careful consideration of risks and benefits.

Timing of Delivery

If your baby shows signs of distress or severe growth restriction, early delivery may be recommended. The goal is to balance the risks of continued pregnancy against the risks of prematurity.

What Does This Mean for Future Pregnancies?

If you’ve had placental blood clots in a previous pregnancy, your risk is higher in subsequent pregnancies. However, with proper management, many women go on to have healthy babies. Your healthcare team will likely recommend:

• Consultation with a maternal-fetal medicine specialist before conception
• Possible thromboprophylaxis (preventive blood thinners) throughout the next pregnancy
• Enhanced monitoring with more frequent ultrasounds
• Testing for underlying clotting disorders if not previously done

Understanding your risk factors and the cause of clots in the previous pregnancy helps guide prevention strategies.

When Should You Seek Immediate Medical Care?

Do not hesitate to go to the hospital or call your healthcare provider if you experience:

• Sudden, severe abdominal or back pain
• Heavy vaginal bleeding
• Significant decrease in your baby’s movements
• Dizziness, lightheadedness, or feeling faint
• Severe headache with visual changes

These symptoms may indicate placental abruption or other emergencies requiring immediate evaluation and treatment.

Moving Forward With Knowledge and Support

Placental blood clots represent a serious complication, but awareness of risk factors and warning signs enables early detection and intervention. If you have risk factors for placental clots, working with a high-risk pregnancy specialist ensures you receive appropriate monitoring and preventive care. Regular prenatal care remains your best protection, allowing your healthcare team to identify potential problems before they become critical.

Remember that most pregnancies, even in women with risk factors, result in healthy outcomes when properly managed. If you’ve experienced complications from placental blood clots, seeking explanations about what happened and why can help you understand your baby’s birth injury and plan for future pregnancies with confidence.