Hematologist
CION Cancer Clinics
Which blood thinners are safe in pregnancy? | CION Cancer Clinics
Heparin injections, usually low molecular weight heparin, are the blood thinner most often used in pregnancy, because they do not cross to the baby. Warfarin is generally avoided, and the newer tablets such as apixaban and rivaroxaban are not recommended. If you already take one and find you are pregnant, call your prescribing doctor the same day and do not stop it on your own. This page explains the options and what to ask. At CION Cancer Clinics, our haematologist cares for anaemia, bleeding, clotting and inherited blood disorders, with ArogyaSri, CGHS and cashless insurance accepted.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- Which blood thinners are safe to use in pregnancy?
- How do the common blood thinners compare in pregnancy?
- Why might you need a blood thinner while pregnant?
- What should you do if you take a blood thinner and want a baby, or find you are pregnant?
- What do families worry about with injections, and what is true?
- Which blood thinners are safe while breastfeeding, and what can this page not tell you?
- Common questions about blood thinners in pregnancy
The short answer
Which blood thinners are safe to use in pregnancy?
Heparin injections, most often low molecular weight heparin, are the usual choice in pregnancy because they do not cross the placenta to the baby. Warfarin and the newer blood-thinning tablets are generally avoided, with a few carefully planned exceptions.
Why the injection is preferred over a tablet
A heparin molecule is too large to pass from your blood into the baby's. It thins your blood without thinning the baby's. Warfarin is small enough to cross, and in early pregnancy it can affect how the baby's bones and face develop. Later it can raise the chance of bleeding in the baby. The newer tablets, such as apixaban, rivaroxaban and dabigatran, have not been studied enough in pregnancy to be considered safe.
Why this is never a decision to make alone
The right medicine depends on why you need it. A woman with a past clot, a woman with a mechanical heart valve and a woman with a clotting disorder may each be advised differently. Your obstetrician and haematologist weigh the risk of a clot against the risk of bleeding, and that balance changes as the pregnancy moves on.
This page gives no doses. Never start, stop or change a blood thinner on your own. The treating team sets the plan.Side by side
How do the common blood thinners compare in pregnancy?
Medicine
How it is usually viewed in pregnancy
Low molecular weight heparin, such as enoxaparin (injection)
The usual first choice. Does not reach the baby. Also used after delivery.
Unfractionated heparin (injection or drip)
Sometimes used close to delivery or with kidney problems, because its effect wears off faster.
Warfarin (tablet)
Generally avoided, especially early on. A specialist may still advise it for some mechanical heart valves.
Apixaban, rivaroxaban, dabigatran (tablets)
Not recommended in pregnancy or while breastfeeding. Usually switched before or as soon as pregnancy is known.
Low-dose aspirin (tablet)
Used for other reasons, such as lowering the chance of pre-eclampsia. It does not replace heparin for a clot.
Not sure whether this applies to you?
Ask an oncologistReasons it is advised
Why might you need a blood thinner while pregnant?
Most pregnant women never need one. These are the situations where a team is likely to discuss it with you.
A clot now, or in the past
A deep vein thrombosis (a clot in a leg vein) or a clot in the lung during this pregnancy is treated with heparin injections. A clot in the past often means preventive injections this time too.
A mechanical heart valve
This is the hardest situation to plan. The valve needs strong, steady blood thinning, and each option carries a different risk for you and for the baby.
Ask for
- A cardiologist and haematologist together
- A plan made before pregnancy, if possible
A clotting disorder
Antiphospholipid syndrome, or some inherited clotting tendencies, may call for heparin, sometimes alongside low-dose aspirin, especially after earlier pregnancy losses.
High risk after delivery
A caesarean, heavy bleeding, a long hospital stay or several risk factors together may lead to injections for a period after the birth, even if you needed nothing before.
If you already take one
What should you do if you take a blood thinner and want a baby, or find you are pregnant?
Tell your doctor before trying
If you are planning a pregnancy, ask the doctor who prescribes your blood thinner now. A switch can often be planned calmly in advance, rather than in a hurry later.
A positive test: call the same day
If you take warfarin or one of the newer tablets and find you are pregnant, contact your prescribing doctor that day. Do not simply stop the tablet. Stopping suddenly can itself cause a clot.
An early review
Your team decides what to switch to, and when. You will be shown how to give the injection yourself, and a family member can learn too.
A plan for the birth
Heparin has to be timed around labour, a caesarean and any epidural. Ask for this plan in writing well before your due date.
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On a blood thinner and pregnant: signs that need care now
Go to the nearest emergency department or call 108 for heavy vaginal bleeding, vomiting blood, black stools, a severe sudden headache, a fall or blow to the head or bump, sudden breathlessness or chest pain. Tell them you are pregnant and which blood thinner you take. Carry its name with you. Do not take another dose until a doctor has seen you and told you what to do.
Commonly believed
What do families worry about with injections, and what is true?
"Daily injections in the stomach will hurt the baby."
The injection goes into the fat under the skin, not into the womb, and the needle is short. Heparin does not reach the baby. Small bruises at the injection site are common and are not a sign of harm.
"The tablet I was on is fine, so there is no need to switch."
A medicine that was right before pregnancy may not be right during it. Warfarin and the newer tablets behave differently in pregnancy. Only your prescribing doctor can say whether yours should change, so ask early.
"Blood thinners mean I cannot have a normal delivery."
Many women on heparin have a normal delivery. The team times the injections around labour so that bleeding and any epidural can be managed safely. The way you deliver is decided by the usual pregnancy reasons.
"Once the baby is born, the injections can stop."
The weeks after birth are when clot risk is highest. Many women are asked to carry on for a while after delivery. Finish the course your doctor set, and ask before stopping.
After the birth
Which blood thinners are safe while breastfeeding, and what can this page not tell you?
Heparin and warfarin are both considered compatible with breastfeeding, because very little reaches the baby through milk. The newer tablets are usually avoided while you are feeding, because there is not enough information about them yet.
Who heparin does not suit
Heparin is not right for everyone. It is used with great care, or not at all, if you are actively bleeding, have a very low platelet count, have had a reaction to heparin before, or have severe kidney problems. Your team will usually check your platelets and kidney function first.
What this page cannot tell you
It cannot tell you whether you need a blood thinner, which one, how much, or for how long. It cannot weigh a mechanical valve against the baby's safety. Those answers come from your own history, your blood tests and a team that knows both.
Getting a haematology opinion
If you have a past clot, a clotting disorder or a heart valve and are pregnant or planning to be, ask for a haematologist to be involved early. At CION, Dr. Basudev Pokhrel reviews these cases with your obstetrician so the plan for pregnancy, the birth and afterwards is agreed in advance.
Questions we are asked
Common questions about blood thinners in pregnancy
Is enoxaparin safe for my baby?
Enoxaparin is a low molecular weight heparin, the type most often used in pregnancy. It does not cross the placenta, so it does not thin the baby's blood or affect how the baby develops. Your doctor will still explain why you need it and how long the course is likely to run.
I took warfarin before I knew I was pregnant. What now?
Contact your prescribing doctor the same day and do not stop the tablet on your own. The team will plan a switch and arrange a detailed pregnancy scan. Many women in this situation go on to have healthy babies, but only your doctors can assess your own timing and risk.
Can I give the injections myself at home?
Yes, most women do. A nurse shows you how to pinch the skin, inject and dispose of the needle safely. A husband, mother or sister can learn too. Change the site each time, and keep the used needles in a hard container away from children.
Why are my platelets being checked?
Rarely, heparin can cause a drop in platelets, the cells that help blood clot. Your team may check a platelet count before and after starting. Reference ranges differ between laboratories, so one result is always read alongside your symptoms and any repeat test.
Can I have an epidural if I am on heparin?
Often yes, but the timing matters. The anaesthetist needs to know exactly when your last injection was given, because a spinal or epidural needle too soon after heparin can cause bleeding near the spine. This is why your birth plan should be written down before labour starts.
Is aspirin the same as a blood thinner injection?
No. Low-dose aspirin works on platelets and is mainly used in pregnancy to lower the chance of pre-eclampsia, a blood pressure problem. It is not strong enough to treat or prevent a clot in a woman who needs heparin. Take it only if your doctor has advised it.
I bruise easily on the injections. Should I stop?
Small bruises where you inject are common and expected. Do not stop on your own. Tell your team at the next visit. Seek care urgently for large spreading bruises, bleeding gums that will not settle, blood in your urine or stool, or any heavy vaginal bleeding.
Are these injections covered by Aarogyasri or insurance?
Cover depends on your scheme, the reason for treatment and whether it is given during a hospital stay. Aarogyasri, PM-JAY, CGHS, ECHS, EHS and cashless insurance rules each differ, and they change, so check the current rules with your scheme or insurer before you rely on them.
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Dr. Basudev Pokhrel reviews blood counts, transfusion needs and blood disorders, and works with the CION tumour board on blood cancers.
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Sources
- NHS — Anticoagulant medicines
- NHS — Warfarin
- NHS — Apixaban
- American Society of Hematology — Blood Clots
- National Heart, Lung, and Blood Institute — Venous Thromboembolism
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Clotting Risk in Pregnancy and After DeliveryWho is at risk of a clot, and the warning signs to act onLow Platelets in Pregnancy: Usually BenignWhy your platelet count is checked before and during heparinPostpartum Haemorrhage and Iron RecoveryBleeding after birth and rebuilding your haemoglobinBenign Haematology in PregnancyEvery blood problem in pregnancy, in one place
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