Deep vein thrombosis (DVT) is a blood clot that develops in the leg, thigh, or pelvis. It’s not common during pregnancy, but pregnant women are 5 to 10 times more likely to develop DVT than nonpregnant women.

The level of blood-clotting proteins increases during pregnancy, while anticlotting protein levels decrease. The enlarged uterus during pregnancy may also increase risk because it puts the veins of the lower body under additional pressure to return blood to the heart.

Read on to learn more about DVT and pregnancy.

The most obvious symptom of DVT is swelling and heavy pain or extreme tenderness in one of your legs. Up to 80 percent of DVT cases in pregnancy occur in the left leg.

Other symptoms of DVT include:

  • pain in the leg when standing or moving around
  • pain in the leg that worsens when you bend your foot up toward your knee
  • warm skin in the affected area
  • red skin at the back of the leg, typically below the knee
  • slight to severe swelling

Is it a muscle cramp or a symptom of DVT?

Muscle cramps are common during pregnancy. They typically affect the calf, particularly at night during the second and third trimesters. They can be prevented with:

  • stretching
  • magnesium supplements
  • comfortable, supportive footwear

Stretching and moving around will not improve pain from DVT. Muscle cramps will not cause your leg to appear swollen.

Pulmonary embolism vs. DVT

Another type of blood clot is pulmonary embolism (PE), a blood clot in the lungs. PE is rare during pregnancy, but more common than in nonpregnant women. Symptoms of PE include:

  • sudden shortness of breath
  • chest pain or tightness in the chest
  • a cough that produces blood-streaked sputum
  • rapid heartbeat

See your doctor as soon as possible if you suspect DVT. While it’s not a medical emergency and is unlikely to harm you or your baby unless there are serious complications, it’s best to get checked early.

It’s not always easy to diagnose DVT in pregnancy from symptoms alone. Your doctor may recommend a blood test called a D-dimer test. A D-dimer test is used to identify pieces of blood clot that have dispersed into your bloodstream.

An ultrasound scan will also be carried out to confirm DVT, because blood clot fragments can increase during pregnancy. A Doppler ultrasound, which is a type of scan that can determine how fast the blood is flowing through a blood vessel, can help doctors establish whether blood flow is slowed or blocked. Slowed or blocked blood flow can be a sign of a blood clot.

If a D-dimer test and ultrasound scan cannot confirm a DVT diagnosis, your doctor may use a venogram. This involves injecting a liquid called a contrast dye into a vein in your foot. The dye moves up the leg and can be picked up by X-ray, which pinpoints a gap in the blood vessel where the blood flow is stopped by a clot.

DVT is easy to treat during pregnancy. Your doctor will refer you to a specialist obstetrician, hematologist (blood specialist), or maternal medicine or obstetric medicine specialist.

To treat the DVT, the blood-thinning agent heparin will be injected daily to:

  • stop the clot from getting bigger
  • help the clot dissolve in the body
  • reduce the risk of further clots

You will have regular checkups and blood tests to ensure the clot has dissolved and no further clots have appeared.

DVT during pregnancy does not affect the baby unless there are serious complications. Heparin is safe to use during pregnancy because it doesn’t cross the placenta, so there is no risk to your baby. Your pregnancy should continue as normal.

The injections will be stopped as soon as you begin normal labor, or 24 hours before labor is induced or a planned cesarean delivery takes place.

If you want to breastfeed your baby, you will have to stop the injections after birth and take a tablet called warfarin (Coumadin) to ensure the baby’s blood doesn’t thin.

Long-term DVT can lead to permanent swelling of the veins and fluid retention. In rare cases, the clot dislodges and moves to the lungs, resulting in a PE.

Factors that increase your risk for DVT during pregnancy are:

  • previous history of clots or DVT
  • family history of DVT
  • being over 35
  • having a BMI of 30 or more
  • carrying twins or multiple babies
  • fertility treatment
  • having had a previous, recent cesarean delivery
  • sitting still for long periods of time
  • smoking
  • being overweight or obese
  • having preeclampsia, or certain chronic illnesses such as hypertension and inflammatory bowel disease
  • severe varicose veins

Learn more about DVT risks »

No single thing will prevent DVT in pregnancy, but there are several steps you can take to reduce your risk:

  • Stay active with pregnancy-safe exercises.
  • Wear flight socks on flights and walk around at least once every hour.
  • Move your legs when sitting down, for example by raising and lowering your heels and your toes, and flexing your ankle.
  • Wear support hose.
  • Quit smoking.
  • See your healthcare provider immediately if you notice any pain, tenderness, redness, or swelling in your legs.

Pregnant women at high risk of DVT may be given a preventative dose of heparin, either during the entire pregnancy or for six to eight weeks postpartum.

DVT isn’t common in pregnancy, but it is a serious condition that can be fatal if the clot dislodges and moves into the lungs. Be aware of the symptoms and risks factors, and let your doctor know right away if you suspect DVT. Early treatment can help keep you and your baby safe.