Antiphospholipid syndrome (APS)

Antiphospholipid syndrome is an immune system disorder. It can cause pregnancy complications, but treatment can help to reduce the risks for you and your baby.

What is antiphospholipid syndrome (APS)?

Antiphospholipid syndrome (sometimes known as sticky blood syndrome or Hughes syndrome), is an immune system disorder that increases the risk of blood clots.

What causes APS?

We are not sure exactly why people develop APS. But experts think it is caused by a combination of genetic and environmental factors. Things that may trigger APS, include:

  • having a family member with antiphospholipid antibodies
  • viral infections, such as CMV or slapped cheek syndrome
  • bacterial infections, such as E. coli
  • certain medications, such as anti-epileptic medicine or the oral contraceptive pill.
  • lifestyle factors such as lack of exercise smoking, obesity and a poor diet.  

But some people without any of these risk factors still develop APS.

What are the symptoms of APS?

If you have APS you have a higher risk of:

  • deep vein thrombosis (DVT), a blood clot that can develop in the leg
  • arterial thrombosis (a clot in an artery), which can cause a stroke or a heart attack
  • blood clots in the brain, leading to problems with balance, mobility, vision, speech and memory.

People with APS may also experience any of the following symptoms:

  • balance and mobility problems
  • vision problems, such as double vision
  • speech and memory problems
  • a tingling sensation or pins and needles in your arms or legs
  • fatigue (extreme tiredness)
  • repeated headaches or migraines.

How can antiphospholipid syndrome affect pregnancy?

APS has been linked to these pregnancy complications:  

Sadly, having APS can also increase your risk of:

If you have APS and are pregnant this may be difficult to read. But try to remember that the risks are reduced if you have treatment and you are monitored carefully in pregnancy. APS is also one of the most treatable causes of recurrent miscarriage.

How is APS diagnosed?

Speak to your GP if you are concerned you may have symptoms of APS. They may be able to refer you for tests at your local hospital.

If you have miscarried before, your GP may also refer to you a doctor who specialises in miscarriage

The NHS follows guidelines that recommend that your GP should refer you to this specialist after you have had 3 early miscarriages in a row or 1  late miscarriage.

In some areas you might be referred to a specialist after 2 miscarriages so it’s worth asking about it. Talk to your GP, explain how you are feeling and ask to be referred.

Find out more about getting referred to a specialist after a miscarriage.

Your doctor will talk to you about your medical history. They will ask if you have had:

  • 1 or more confirmed blood clots
  • 1 or more late miscarriages at or after week 10 of your pregnancy
  • 1 or more premature births at or before week 34 of your pregnancy
  • 3 or more early miscarriages before week 10 of your pregnancy.

If your healthcare professional thinks you may have APS you will also be offered blood tests for the antiphospholipid antibodies that increase the risk of blood clots.

You will be diagnosed with APS if you have 2 abnormal blood test results, with at least a 12-week gap between them.  

How is APS in pregnancy treated?

There is no cure for APS. But treatment before and during pregnancy can really improve your chances of having a healthy pregnancy.

Before pregnancy

If you already know you have APS then speak to your GP or specialist before you get pregnant. The sooner you start treatment, the better your chances of having a healthy pregnancy.  

Some medications used to treat APS carry a small risk of harming an unborn baby. Do not stop taking it but talk to your doctor or APS specialist about it before you get pregnant if possible.

During pregnancy

Your team will treat your pregnancy as high-risk. This means that they will keep a careful eye on you throughout your pregnancy.

Your care will be doctor-led, alongside the midwifery team.  You will probably have more blood tests, urine tests and blood pressure checks than usual. You will also have extra scans to check your baby’s growth, and the blood flow through the placenta and cord to your baby.

It can be stressful to have more tests and appointments than you expected. But this extra care will help your medical team make sure that you have a safe pregnancy.  

What medication will I need to take?

You will be asked to take daily doses of aspirin or daily injections or heparin, or both. These medications make your blood less likely to clot and are safe to take while pregnant.

Warfarin is a a routine treatment for people with APS. But it is not recommended during pregnancy because it carries a small risk of causing birth defects. However, if you are taking warfarin to prevent clotting, it is not safe to stop. It must be changed to an alternative anti-clotting drug, which is usually heparin. Speak to your GP or specialist as soon as possible so your medication can be changed safely.

How can I reduce my risk of blood clots in pregnancy?

Along with treatment, there are things you can do to reduce your risk of blood clots and improve your chance of having a healthy pregnancy and baby. These include:

Knowing the signs and symptoms of a blood clot can help you to get the right treatment quickly. Contact your midwife or doctor, or call NHS 111 straight away if you have:

  • a throbbing or cramping pain in your arm or leg
  • swelling, redness or a feeling of warmth in that area.  

Call 999 if you:

  • suddenly find it hard to breathe
  • have pain or tightness in the chest or upper back
  • are coughing up blood.

Your baby’s movements and APS

Feeling your baby move is a sign that they are well. If you notice that your baby’s movements have slowed down, changed or stopped, it may be a sign that your baby is not well.    

Because APS increases the risk of stillbirth it is very important to get to know your baby's usual movements from day to day.  

Reduced baby movements is one of the signs that a baby may not be getting enough oxygen. If you get the right treatment and care as soon as you can this could save your baby’s life.

You should be able to feel your baby move, right up to the time you go into labour, and during labour.

Contact your midwife or maternity unit immediately if you think your baby’s movements have slowed down, stopped or changed.

Find out more about your baby's movements.

Will APS affect how I give birth?

It may be possible to have a vaginal birth if you and your baby are healthy. Your healthcare team may recommend continuous fetal monitoring. This involves being attached to a device that monitors your baby's heartbeat and your contractions all the time.

You may be offered a planned caesarean section if your healthcare team thinks this will be safer for you and your baby.  

How long after the birth do I need to keep taking medication?

You may need to keep taking medication for around 6 to 8 weeks after giving birth to help prevent blood clots. Do not stop taking your medication unless your healthcare professional advises you to.

Can I breastfeed with APS?

Both heparin and warfarin are safe to take if you are breast or chest feeding. Although warfarin is not safe to take during pregnancy, your doctor may prescribe it after you give birth.

It is important to speak to your GP or specialist before you start trying to get pregnant, even if you have been pregnant before.

In the meantime, use contraception every time you have sex. You can get pregnant as soon as 3 weeks after you’ve given birth. This is true even if you’re breastfeeding and you are not having periods.

Find out more about your body after the birth.

Which contraceptive is safe to use with APS?

Women with APS should avoid using contraceptives that contain oestrogen, such as the combined pill or a contraceptive patch. This is because oestrogen can increase the risk of blood clots. 

These types of contraception are safe to use if you have APS:

  • mini-pill (progesterone-only pill)
  • progestogen-only contraceptive injections
  • condoms
  • Mirena coil.

Speak to your midwife, GP or health visitor to learn more.

Where can I find extra support and information about APS?

If you have just been told you have APS, or you are worried about how it may affect your pregnancy, do not hide your feelings or suffer in silence. Share how you feel with your partner, family or friends. Your GP or specialist can help you get any extra support you might need.  

APS Support UK provides advice to those affected by APS in the UK. Their website includes factsheets about living with APS. They also have details of specialists in your area if you’re referred by your GP.

You can also speak to a Tommy’s midwife for free, on 0800 014 7800 (Monday to Friday, 9am to 5pm), or email us at [email protected]

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Bobirca A, Dumitrache A et al (2022)Pathophysiology of Placenta in Antiphospholipid Syndrome. Physiologia 2022, 2, 66–79.

Xi J, Chen D, et al (2022) Antiphospholipid Antibodies Increase the Risk of Fetal Growth Restriction: A Systematic Meta-Analysis. Int J Clin Pract. doi: 10.1155/2022/4308470

Yan Z, Shen X, et al. (2020) Prevention of recurrent miscarriage in women with antiphospholipid syndrome: A systematic review and network meta-analysis.  Lupus. 2021;30(1):70-79. doi:10.1177/0961203320967097

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Bundhun PK, Soogund MZS, et al (2018) Arterial/venous thrombosis, fetal loss and stillbirth in pregnant women with systemic lupus erythematosus versus primary and secondary antiphospholipid syndrome: a systematic review and meta-analysis. BMC Pregnancy Childbirth 18, 212 (2018).

APS Support UK. Pregnancy. 

NHS. Deep vein thrombosis in pregnancy. (Page last reviewed: 23 April 2021, Next review due: 23 April 2024)

Royal College of Obstetricians and Gynaecologists. Your baby's movements in pregnancy.

Erkan D (2022). Patient education: Antiphospholipid syndrome (Beyond the Basics). UpToDate. 

NHS Choices. Your body after the birth. (Page last reviewed: 15 April 2021. Next review due: 15 April 2024)

Erkan D (2022). Patient education: Antiphospholipid syndrome (Beyond the Basics). UpToDate. 

APS Support UK. APS and Women's Health. 

Review dates
Reviewed: 30 June 2023
Next review: 30 June 2026