Key takeaways

Pregnant women are at a higher risk of developing deep vein thrombosis (DVT) due to factors like increased estrogen levels, higher blood coagulability in preparation for childbirth, and physical changes that restrict blood flow.
Conditions such as inherited blood clotting disorders, obesity, age over 35, and certain medical conditions like lupus and sickle cell disease further elevate the risk of DVT during pregnancy.
Symptoms of DVT include swelling, pain or tenderness in the legs, warmth or redness behind the knee, and should prompt immediate medical attention to avoid serious complications.
Prevention and treatment of blood clots during pregnancy can involve the use of anticoagulant medications (such as injectable low-molecular-weight heparin), staying active, wearing compression stockings, and maintaining hydration.

There is nothing quite like the feeling of not being able to catch your breath. When I was 22 years old, I had trouble breathing. I eventually went to the hospital where they diagnosed me with a pulmonary embolism—a blood clot in the lung, a rare condition for a person of my age. I later learned that I had a genetic condition that increased my likelihood of developing a blood clot.

My clot was broken up and I was treated for some time afterward with blood thinners, but I knew that in the future I would need to take proactive measures if I were to become pregnant or have surgery. Blood clots during pregnancy are a concern for many expectant mothers, but as I learned, it is possible to manage your high risk.

What is a blood clot?

Blood clotting is a natural process that occurs when blood clumps together to form a gelatinous mass. This process protects your body from bleeding too much when you’ve been injured, as clotting can seal off the wound. Blood clotting (called thrombosis) can also cause complications, especially when it happens internally in your blood vessels.

This can happen in any blood vessel in the body. However, the most common place for abnormal blood clots to occur is in the deep veins of your legs. This is called deep vein thrombosis (DVT). The major concern is that the clot can break free and travel to other parts of the body (lungs are most common), which can lead to serious complications or even death.

Why are pregnant women at greater risk of blood clots?

In pregnancy, the body is primed to clot to prevent blood loss during delivery. While this is important, it also increases the risk of clotting problematically.

It is estimated that pregnant women may be up to five times more likely to experience blood clots than non-pregnant women. There are several reasons for this uptick. Higher-than-normal levels of estrogen during pregnancy are known to increase clotting risk, although the exact mechanism by which this happens is unknown. Also, a woman’s blood clots more easily in preparation for childbirth in order to reduce blood loss at delivery. Restricted blood flow may also raise the likelihood of blood clots. As the baby gets larger during pregnancy, it places more pressure on the blood vessels in the pelvic region, resulting in a restriction of blood flow that can also cause blood clots. If bed rest is required, lack of movement can decrease blood flow to the arms and legs, also increasing risk.

A blood clot in the lung, also known as a pulmonary embolism, is a leading cause of maternal death for pregnant women in the U.S., according to the CDC. And the risk of developing blood clots isn’t just during the pregnancy—it continues to be a concern for approximately three months after giving birth. Delivery by cesarean section (C-section) nearly doubles your risk after birth.

“Pregnant women are at a higher risk of DVT for several reasons,” says Nisha Bunke, MD, a vein specialist and diplomate of the American Board of Venous and Lymphatic Medicine, “a hypercoagulable state (proteins in the blood make it thicker, and more likely to form clots), an enlarged uterus may put pressure on the veins in the lower abdomen, and the hormones decrease venous tone.”

Anyone can develop a blood clot during pregnancy, however it is more likely under certain conditions, or for those who already have some risk factors. Dr. Bunke adds that “some women have risk factors that increase their risk of DVT even more during pregnancy, like inherited blood clotting disorders, medical conditions such as lupus and sickle cell disease, obesity, immobility and age over 35.”

Other factors that may increase the risk of clotting during pregnancy are:

Family history of blood clots
Multifetal gestation (twins or more)
Being dehydrated
Traveling long distances (sitting for long time periods)
Prolonged stillness, like bed rest during pregnancy
Other medical conditions
Transfusion at delivery
Peripartum cardiomyopathy
Postpartum hemorrhage
Pre-eclampsia

What are other risk factors for blood clots?

In addition to pregnancy, the following risk factors can increase your risk of developing a blood clot.

Acquired:

Smoking
Being overweight or obese (a BMI of 30 or greater)
Having a surgery, hospitalization or illness that necessitates prolonged bed rest
Traveling for long stretches by car or plane with little movement
Being on estrogen-containing contraceptives or hormone replacement therapy
Having cancer

Genetic:

Having a family member who’s had a blood clot
Having a personal history of blood clots
Having a personal history of unexplained miscarriages

Condition-related:

Atherosclerosis
Diabetes
High blood pressure
Vasculitis
Heart failure
Irregular heartbeat
Metabolic syndrome

Additionally, some people may be predisposed to getting blood clots if they have thrombophilias, a group of disorders that increase a person’s risk of thrombosis (abnormal blood clotting). This was my case, with a condition known as Protein C Deficiency.

Symptoms of blood clots during pregnancy

“The most obvious symptom of DVT is swelling and heavy pain or extreme tenderness in one of your legs,” says Kendra Segura, MD, a board-certified OB-GYN in Southern California. Other symptoms include:

Swelling
Pain in the legs while in motion
Skin feels warm or tender
Redness, usually behind the knee
A heavy, painful sensation

Dr. Segura says if you are experiencing these symptoms you must seek medical attention immediately. Your healthcare provider may require further testing because “it’s not always easy to diagnose DVT in pregnancy from symptoms alone,” she says.

What problems are associated with blood clots during pregnancy?

Blood clots during pregnancy can increase your risk of complications including:

Blood clots in the placenta that can inhibit blood flow to your baby, causing damage to a developing fetus.
Heart attack can occur if a blood clot blocks blood flow to the heart.
Intrauterine growth restriction (IUGR), or when your baby does not grow as expected, may occur.
Miscarriage can occur before week 20 of your pregnancy.
Placental insufficiency may occur, reducing the supply of necessary food and oxygen to your baby.
Preeclampsia, a dangerous condition marked by high blood pressure and high levels of protein in the urine, may occur after week 20 in your pregnancy or immediately after childbirth. This can be fatal if not treated.
Premature birth, in which your baby is born prior to week 37 of pregnancy, may occur.
Pulmonary embolism, or a blood clot that moves to the lung, can potentially lower your blood oxygen levels and damage your organs, even leading to death.
Stillbirth, or death of a baby after week 20 of pregnancy, may occur.
Stroke can occur if a blood clot blocks one of the blood vessels that supplies blood to the brain or causes a blood vessel in the brain to burst.
Sudden death
Thrombosis occurs when a blood clot inside of a blood vessel impedes blood flow. Central vein thrombosis (CVT) occurs in the brain, and deep vein thrombosis usually occurs in the leg.
Venous thromboembolism occurs if a blood clot travels to the brain, lungs, or heart.

Bleeding during early pregnancy

Sometimes during pregnancy, women pass blood clots vaginally, which is an understandable cause of concern.

In the first trimester of pregnancy (first three months), women may bleed as a result of implantation (where the fertilized egg attaches to the uterine wall) or due to early pregnancy loss (miscarriage). Implantation bleeding is usually light and not enough to soak a pantiliner. While not all cases of passing clots within the first 12 weeks of pregnancy are indicative of a loss, vaginal bleeding during pregnancy can be indicative of a complication.

For example, bleeding during the first trimester of pregnancy may be caused by a cervical infection, subchorionic hematoma (bleeding from the membranes surrounding the fetus), cervical polyps, ectopic pregnancy, or molar pregnancy (in which a fertilized egg develops into abnormal tissue). That’s why if you experience bleeding of any kind–including blood clots, it’s best to follow up with your obstetrician, gynecologist, or another healthcare professional.

Blood clots that develop in the body can increase the risk of miscarriage, or loss of a fetus prior to 20 weeks of pregnancy. Signs of a miscarriage include vaginal spotting or bleeding, abdominal cramping, back pain, and passing fluid, tissue or blood clots from the vagina. Light vaginal bleeding often occurs during the first trimester, but if you are bleeding or passing blood clots or tissue, seek immediate medical attention and bring the discharge to your provider.

Bleeding in the second and third trimesters

In the second and third trimesters, bleeding could be caused by a variety of factors. These may include miscarriage, preterm labor, or obstetric abnormalities including placenta previa, or placental abruption. Bleeding and especially passing clots during pregnancy can be a sign of miscarriage, preterm labor, or other complications, so make sure to contact your healthcare provider if you experience bleeding.

How to prevent and treat blood clots in pregnancy

When it comes to DVT in pregnancy, prevention is key. In my own case, I was known to have a higher risk due to a thrombophilic disorder, as well as a history of previous clots. This meant that I was given an injectable low-molecular-weight Heparin (LMWH) drug (Fragmin coupons | Fragmin details) for the duration of my pregnancy as a preventive measure.

There are also other preventative measures that can help lower your risk of clots, Dr. Segura says, including:

Wearing compression stockings
Keeping well-hydrated
Staying active (“Regular exercise improves circulation,” Dr. Segura notes.)
Avoid prolonged sitting or bed rest, travel can also be considered prolonged bed rest
Avoiding smoking
Communicating any other medical conditions to your doctor
Keep your blood pressure normal

Although the development of blood clots during pregnancy can be dangerous, they are still fairly uncommon—and treatable. Due to associated risks to you and your developing baby, getting diagnosed and treated as soon as possible is crucial.

Anticoagulant medications (also known as blood thinners) can be prescribed to help to break up the clot and get the blood moving again. Dr. Segura says that both Heparin and low-molecular-weight Heparin are safe in pregnancy for mother and baby. The main side effect of taking blood thinners is an increased risk of bleeding, so your doctor will monitor you as the pregnancy progresses.