Learning About Taking Anticoagulants During Pregnancy

Anticoagulants are medicines that prevent blood clots from forming in your blood vessels and heart. They also keep blood clots from growing bigger.

People often call them blood thinners. But they don't really thin the blood. They slow down the time it takes for a blood clot to form.

Changes in hormones and blood flow during pregnancy and after delivery increase the risk of blood clots. You may need a blood thinner if you have:

• Venous thromboembolism (VTE). If you are diagnosed with VTE, you need a blood thinner to treat it. VTE is a blood clot in a vein and includes deep vein thrombosis (DVT) and pulmonary embolism. DVT is a clot in a vein that is deep under the skin, often in the leg. If the clot breaks apart, pieces of it can travel to the lungs (pulmonary embolism). This is a medical emergency.
• A higher risk for VTE. Pregnancy already makes clots more likely. So your doctor may suggest a blood thinner if something raises your risk even more, such as if you have had DVT before.
• Atrial fibrillation (AFib). The heart beats in an irregular pattern.
• Left ventricular dysfunction. The muscles of the left ventricle of the heart can’t pump enough blood to the body.
• A blood clotting condition (thrombophilia). Some people inherit or develop conditions that make clots more likely.
• An artificial heart valve. Blood clots can form on the valve flaps and break off.

• Low-molecular-weight heparin (LMWH). This is the medicine most given to prevent VTE during pregnancy and for at least 6 weeks after delivery. It can be started during the first trimester and is considered safe for the fetus. It is given as a shot.
• Unfractionated heparin (UFH). The benefit of this medicine is that its effect wears off quickly after you stop taking it. So it can be stopped quickly before delivery or other pregnancy events. It is given as a shot.
• Warfarin. This is a pill that is not normally used during pregnancy except in certain cases.
• Direct oral anticoagulants (DOACs). These are pills that many people take outside of pregnancy. But they are not considered safe during pregnancy. If you take one of these and are pregnant or planning to become pregnant, talk to your doctor about switching to a safer option. Do not stop taking it on your own.

Because blood thinners prevent clots, they can also raise the risk of serious bleeding, especially during labor and delivery. Your doctor will use them only when the benefits of the medicine are greater than the risks.

Warfarin crosses the placenta during pregnancy. This means it can cause birth defects and affect the fetus's blood clotting. So its use is avoided, especially during the first trimester. But it's good at preventing clots when an artificial heart valve is present. If you have an artificial valve, you and your doctor will weigh the risks of getting VTE and blood clots from the valve against the risk of using warfarin.

The best way to make sure that a blood thinner is safe for you during your pregnancy is to work closely with your doctor. Using these medicines is challenging because of the possible risks to the fetus. If you take blood thinners for an ongoing condition, such as atrial fibrillation, it's especially important to get specialized counseling before and during pregnancy on how to manage your medicine safely.

Using a blood thinner during labor and delivery is risky. Blood loss while giving birth is normal. If you've been taking a blood thinner while pregnant, your doctor may stop it before delivery or before getting an epidural and restart it later. You'll be under the close supervision of your care team the whole time.

In most cases, your blood thinner can be restarted after delivery. Your doctor or midwife will recommend when to restart it based on how you delivered, whether you had an epidural, and your bleeding risk. And your doctor will select one that doesn't affect your breast milk.

While you are taking a blood thinner, it's important to be aware of any signs of serious bleeding and to get emergency help. Get emergency care if you have signs such as bleeding that won't stop or a severe headache, or if you have a hard fall or hit to the head. And contact your doctor or midwife if you have other unusual bleeding, like blood in your urine or stool. Also get medical help right away if you have symptoms of a blood clot. These include pain, swelling, or redness or another change in color on your leg.