Anemia, Iron & Blood Health
Blood Clots in Pregnancy and Postpartum: Signs, Risks and Prevention
Pregnancy raises your risk of blood clots, and that risk stays high for up to 3 months after birth. The CDC notes women are about five times more likely to have a blood clot during pregnancy and the postpartum period. Clots are treatable and often preventable, so the most useful thing you can do is know the warning signs and know which ones mean 911.
Why pregnancy makes your blood clot more easily
This is your body being protective. It's getting ready to stop bleeding at delivery, so your blood clots more easily for months. A few other changes stack on top:
- Clotting factors rise and your natural anticoagulants fall
- Blood flow in the legs slows as the growing uterus presses on the big veins in your pelvis
- You move less, especially on bed rest or after a cesarean
- Blood vessels get injured during delivery, especially with surgery
DVT and PE, in plain terms
| Condition | What it is | Why it matters |
|---|---|---|
| Deep vein thrombosis (DVT) | A clot in a deep vein, usually the leg or pelvis | Can break loose and travel to the lungs |
| Pulmonary embolism (PE) | A clot that has traveled to the lungs | Can be life-threatening; needs emergency care |
Together they're called venous thromboembolism (VTE). The CDC's maternal mortality surveillance lists blood clots among the causes of pregnancy-related deaths in the U.S. That's not meant to frighten you. It's why your team takes leg pain and breathlessness seriously, and why you should too.
The warning signs
A clot in the leg (DVT)
- Swelling in one leg or arm
- Pain or tenderness, often in the calf or thigh, that isn't from an injury
- Skin that's red, warm or discolored
- One leg clearly bigger than the other
In pregnancy, DVT shows up more often in the left leg.
Here's the part everyone asks about: puffy feet and ankles on both sides, especially at the end of the day, are normal in pregnancy. Calf cramps at night are common too. What's not normal is one leg that's swollen, sore and warm when the other isn't. A quick check: compare your calves side by side in the mirror, or ask your partner to look.
A clot in the lungs (PE): call 911
- Sudden shortness of breath
- Chest pain, especially when you breathe in
- A fast or irregular heartbeat
- Coughing, sometimes with blood
- Feeling faint or passing out
Being a little winded climbing stairs in the third trimester is expected. Breathlessness that comes on suddenly, at rest, or with chest pain is not. Don't drive yourself, and don't wait to see if it passes.
Who's at higher risk?
Your risk is higher if you:
- Have had a blood clot before
- Have an inherited clotting condition (thrombophilia), such as Factor V Leiden
- Have a close family member who had a clot
- Have a cesarean birth
- Have obesity
- Are older (often cited as over 35)
- Smoke
- Are carrying twins or more
- Have preeclampsia, infection, heavy bleeding after delivery or a long hospital stay
- Have certain medical conditions, such as lupus, sickle cell disease or heart disease
- Are on bed rest or travel long distances without moving
- Conceived with IVF
If any of these apply, say so at your first prenatal visit. Family history especially tends to get skipped, so ask your relatives before you go: has a parent, sibling or aunt ever had a clot in the leg or lung, or been on blood thinners?
How doctors check for a clot
- Leg ultrasound is usually the first test for DVT. It's the same gel-and-probe ultrasound you know from prenatal scans, pressed a bit firmer along the vein. No radiation.
- CT scan or lung scan (V/Q scan) may be used for a suspected PE. These are considered safe enough in pregnancy when needed, because missing a PE is far more dangerous than the small radiation dose.
- D-dimer blood tests are less useful in pregnancy, because levels rise naturally.
How clots are treated in pregnancy
Blood thinners (anticoagulants) stop a clot from growing and lower the chance of new ones.
- Low molecular weight heparin (LMWH) is usually preferred. It's an injection under the skin, usually in the belly, and it doesn't cross the placenta. Most people learn to do it themselves in one visit. Bruising at the site is common.
- Unfractionated heparin may be used in some situations, such as around delivery.
- Warfarin is generally avoided during pregnancy but can be used after birth, including while breastfeeding.
- Direct oral anticoagulants (DOACs) are generally avoided in pregnancy and breastfeeding.
Your team will plan how to time blood thinners around labor and an epidural, so ask early what to do when contractions start. Never stop or change a blood thinner without talking to your clinician.
Can clots be prevented?
For everyone:
- Stay active as your provider allows
- Walk and stretch your legs often on long trips
- Drink water
- Get up and walk as soon as you safely can after delivery, even just to the bathroom and back
For some people, preventive blood thinners (prophylaxis) are recommended during pregnancy, after delivery, or both. Per ACOG and ASH, that decision depends on your personal history of clots, any thrombophilia, family history and other risk factors. Compression devices (the sleeves that squeeze your calves) are also commonly used during and after a cesarean. They're noisy and a little annoying. Keep them on.
Long trips while pregnant
Sitting still for hours raises clot risk. On flights, long train rides, or the drive upstate or out to the East End:
- Get up and walk every hour or two when it's safe (on the road, plan rest stops)
- Flex and point your feet and do ankle circles while seated
- Drink water
- Pick an aisle seat if you can
- Ask your provider whether compression stockings make sense for you
Questions to ask your provider
- Do I have risk factors that raise my chance of a clot?
- Should I be tested for a clotting disorder, given my personal or family history?
- Do I need preventive blood thinners in pregnancy, after delivery, or both?
- If I have a cesarean, what will be done to lower my clot risk?
- What should I do on long car rides or flights?
- What symptoms mean I go straight to the ER?
When to call your provider
Call your OB/GYN or midwife the same day for:
- New swelling, pain or warmth in one leg
- A leg that looks red or discolored
Call 911 for:
- Sudden shortness of breath
- Chest pain
- Coughing up blood
- Fainting
Tell every provider you see, including in the emergency room, that you're pregnant or recently gave birth. ER staff don't always ask, and "I had a baby five weeks ago" changes how they think about chest pain.
If you've had a clot before or have a known clotting disorder, ask about seeing a maternal-fetal medicine specialist, ideally before or early in pregnancy. Many MFM practices in the city are attached to the large hospital centers; you can browse MFM specialists in Manhattan or search for an OB/GYN near you.
Seeing a hematologist in New York
If you've had a clot, have a known clotting disorder, or are on blood thinners, a hematologist often works alongside your OB team to plan pregnancy and postpartum care. Premier Hematology & Oncology, which sponsors our professional resources, offers hematology consults at centers across NYC, Long Island and the Hudson Valley. Clinicians can find referral details on our hematology partners page.
Frequently asked questions
How common are blood clots in pregnancy?
Clots are still uncommon in any one pregnancy, but the CDC notes women are about five times more likely to have a blood clot during pregnancy and the months after birth than when they're not pregnant.
How long after giving birth are you at risk for blood clots?
The CDC says risk stays elevated for up to 3 months after delivery, and it's highest in the first weeks after birth.
What does a blood clot in the leg feel like in pregnancy?
Usually swelling, pain or tenderness, warmth and redness in one leg. Cramps and mild swelling in both legs are common in pregnancy, so the thing to watch for is one leg that's clearly different from the other.
Are blood thinners safe in pregnancy?
Heparin-type blood thinners, especially low molecular weight heparin, are the usual choice in pregnancy because they don't cross the placenta. Some other blood thinners are avoided. Your care team decides whether you need one.
Sources
- ACOG — Practice Bulletin 196: Thromboembolism in Pregnancy
- ASH — 2018 Guidelines for Management of Venous Thromboembolism: Venous Thromboembolism in the Context of Pregnancy
- CDC — Blood Clots and Pregnancy
- CDC — Pregnancy Mortality Surveillance System
- NHLBI — Venous Thromboembolism
This article is for general education and is not medical advice. It does not replace an evaluation by a licensed clinician who knows your history. If you think you have a medical emergency, call 911.