Deep vein thrombosis (DVT) in pregnancy

What is deep vein thrombosis (DVT)?

Deep vein thrombosis (DVT) is a blood clot (thrombus) that happens in the deep veins of the lower leg (most commonly), thigh, pelvis, or arm. A blood clot can keep the blood from traveling back to the heart as it should. The clot can also travel to other parts of the body and cause blockages there.

An untreated blood clot can break off within the vein and travel to arteries of the lungs, where it can cause a pulmonary embolism (PE). A PE can be fatal, as it can stop blood from being oxygenated within the lungs. It happens in 1 in every 1,600 pregnancies and accounts for 9 percent of maternal deaths.

Blood clots can also form closer to the surface of the skin. This is called superficial thrombophletis and is less serious than deep vein blood clots. If you have superficial thrombophletis, you might experience redness, pain, and even a skin infection in the surrounding area.

Pregnant women can also get blood clots in the ovarian veins, umbilical cord, and placenta. When clots involve the placenta or baby, they can cut off blood flow and cause miscarriage, growth restriction, or stillbirth.

How common is deep vein thrombosis in pregnancy?

Women who are pregnant are five times more likely to have a blood clot than women who are not pregnant. They're also at higher risk during childbirth and up to 3 months after delivery. DVT happens in 1 in 500 to 2,000 pregnancies. The risk of a blood clot is highest in the first week after delivery, when it increases by 100-fold.

Why DVT is more common in pregnancy:

• Your blood clots more easily during pregnancy, thanks to naturally increased levels of estrogen. This is a good thing during labor and delivery, when it helps lessen blood loss.
• The pressure in the veins in your legs and pelvis increases when you're pregnant.
• Your venous return (blood flow back to the heart) is made more difficult as the growing baby presses on your large abdominal and pelvic veins. Blood flow will also be limited if you have significantly decreased mobility and are sitting or lying down a lot more than usual.

Venous thromboembolism (VTE) — which includes DVT and PE — is two to five times more common postpartum than during pregnancy. The risk is highest in the first six weeks after delivery, then it declines to rates similar to the general population by about 13 to 18 weeks.

What are the risk factors for DVT in pregnancy?

Risk factors for DVT in pregnancy or postpartum include:

• A personal or family history of blood clots or a blood clotting disorder
• A cesarean section
• Prolonged immobility (such as bedrest or activity restriction or travel for more than 4 hours).
• Carrying multiples
• Fertility treatments involving the use of hormones
• Certain medical conditions, such as heart or lung conditions, diabetes, inflammatory bowel disease, urinary tract infections, hypertension, eclampsia or preeclampsia, kidney problems
• Smoking. Smoking damages the lining of blood vessels, which can cause blood clots.
• Being overweight or obese
• A recent severe infection or injury, such as a broken bone
• Surgery
• Maternal age 35 or older
• Preterm delivery (earlier than 36 weeks)
• Obstetric hemorrhage
• Stillbirth
• Postpartum infection
• Currently undergoing cancer treatment (chemotherapy or radiation) or have cancer
• Dehydration. Being dehydrated causes your blood vessels to narrow and your blood to thicken.
• Severe varicose veins (painful, above the knee, with redness or swelling)
• A long labor
• COVID 19 infection

The more of these risk factors you have, the higher your chances of developing a blood clot during pregnancy or postpartum.

How will I know if I have blood clots during pregnancy?

It's important to know the signs and symptoms of a blood clot, because early treatment can keep a DVT from traveling to the lungs. Call your doctor right away if you notice:

• One-sided swelling of an arm or leg, usually in the calf area
• Pain, aching, or tenderness in the area. Unlike muscle cramps, DVT pain won't get better if you stretch or move around.
• Skin that's warm to the touch, red, or discolored

Call 911 for emergency medical treatment if you have any of these signs of a PE:

• Difficulty breathing or shortness of breath
• Sharp chest pain that worsens when you breathe
• Coughing up blood
• A heartbeat that's faster than normal or irregular

To confirm that you have a blood clot, your healthcare provider may use:

• Laboratory tests
• An ultrasound, to see if blood flows freely in the suspected veins
• A CT or Computed Tomography scan, especially if there's a concern about a pulmonary embolus (PE), to look specifically for the blood clot in the veins of the lungs
• A V/Q scan or ventilation/perfusion scan to identify areas of the lung possibly affected by a clot

What are the risks of blood clots?

In addition to a dangerous pulmonary embolism, the risks of blood clots include:

• Intrauterine growth restriction (IUGR) can happen because a blood clot can keep your baby from receiving the blood flow and oxygen they need to grow properly.
• Miscarriage or stillbirth. If blood clots form in the placenta, it can decrease the supply of nutrients and blood to your baby, resulting in miscarriage or stillbirth. This is more likely to happen in women who are already at high risk of developing a blood clot.
• Placental insufficiency
• Preeclampsia
• Premature birth

What are some ways I can prevent blood clots during pregnancy? 

• Talk with your healthcare provider about your risk of blood clots (including your history of problems with blood clots in the past), and come up with a plan to reduce your chances of developing one.
• Know the signs and symptoms so you can get treatment as soon as possible, if necessary.
• Stay active. Regular exercise helps blood flow throughout your body, while sitting for long stretches limits blood flow and make a blood clot more likely. If you're sitting for long periods of time (at work or while traveling, for example), do leg stretches and get up and walk around when possible.
• When on a long trip, wear loose, comfortable clothes, don't smoke beforehand, and avoid alcohol or any medications that may make you sleepy, because you'll be less likely to move around.
• Wear knee-high compression stockings if you are at risk of blood clots
• Stay hydrated.
• Maintain a healthy weight.
• Take any medications you've been prescribed. If you're at high risk for DVT, your provider may prescribe anticoagulants as preventative therapy.

How is deep vein thrombosis treated?

The goals in treating DVT are preventing:

• PE
• The clot from getting bigger
• New blood clots from forming
• Long-term complications

Possible treatments include:

Medications

Medications called anticoagulants can keep the blood clot from getting bigger and from travelling to the lungs. The medication also prevents new clots from forming. If you've had a blood clot, you're at increased risk of developing another one, especially in the first few months.

These are typically given as injections throughout the duration of your pregnancy and six weeks postpartum. The injected medication is most often a low-molecular weight heparin called lovenox. Injectable heparins are entirely safe during pregnancy.

Some of the medications that are commonly used to treat blood clots are usually avoided during pregnancy. For example, warfarin (brand name Coumadin), a common anticoagulant, is generally avoided during pregnancy because it crosses the placenta and is associated with specific fetal heart defects. Rarely, very high-risk individuals will be prescribed warfarin in pregnancy.

Some tips for DVT treatment:

• Follow your provider's directions exactly. She'll tell you when to take your medication, and she may make dietary recommendations (because some foods may not be compatible with your medications, for example).
• Watch for signs of bleeding, because anticoagulants can make it more difficult for your body to control bleeding after an injury.
• If you miss a dose of your medication, call your healthcare provider for advice.
• Wear an alert tag to let emergency staff know that you're on an anticoagulant and at risk of excessive bleeding.
• Get regular checkups so your provider can make sure that you have no new blood clots and that the original clot is gone. Depending on what medication you're taking, you may need to have regular blood tests to see how your blood is clotting.

Thrombolytic therapy

If your case is severe, you may receive intravenous medication to dissolve the blood clot. This may be necessary if you've had serious complications related to DVT or PE, or if the clot is in danger of cutting off blood supply to your leg and causing gangrene, for example. This therapy is best used soon after diagnoses of DVT or PE. If the intravenous medication doesn't work, surgery may be needed to remove the clot.

Inferior vena cava filter

If medications don't work (or you can't take them), your provider may recommend an inferior vena cava filter (IVC filter). This filter traps any large clots from entering the large vein that carries blood from the lower half of your body back to your heart. It's inserted through a small incision in a leg vein using local anesthetic.

How will DVT affect my labor and delivery?

If you're taking a longer-acting injection (such as lovenox) during pregnancy, your provider will likely switch to a shorter-acting heparin at around 36 weeks. This is so when labor begins it will wear off more quickly and allow you to get an epidural if you desire. Your anesthesiologist may want to check your blood's ability to clot prior to placing the epidural, so make sure you tell your labor team when you took your last blood thinner.

Your doctor will stop your injections when labor begins. If you're having a planned cesarean delivery or an induced labor, the injections will be stopped at least 12 to 24 hours beforehand (depending on which medication you're being given).

After delivery, you'll be restarted on blood thinners and continue to take them until six-weeks postpartum. Heparin and lovenox injections are safe while breastfeeding, as is warifin. Talk with your provider about the safest choices for you and your baby.

Learn more about DVT in pregnancy

Visit the National Blood Clot AllianceOpens a new window website for more information on blood clots, including risks, symptoms, and patient stories.

Learn more:

• 12 steps to a healthy pregnancy
• Pregnancy symptoms you should never ignore
• The best kinds of exercise for pregnancy
• Your pregnancy diet: The basics of eating well