Information alert

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You have been given this leaflet because your midwife or sonographer has recommended that you take aspirin based on certain risk factors (see here). 

What is aspirin?

Aspirin is a non-steroidal anti-inflammatory drug (NSAID). Taking a low dose of aspirin (150mg) is often used in pregnancy to reduce the risk of developing pre-eclampsia.

When should I start taking low dose aspirin and for how long?

If low dose aspirin has been recommended, you should start taking it before 16 weeks in order to get the most benefit. Do not start aspirin after 20 weeks as there is no evidence that it helps to prevent pre-eclampsia.

The recommended dose of aspirin is 150mg every evening with food. 

You should continue taking aspirin until 36 weeks of pregnancy. 

It is also recommended that you stop taking aspirin if you experience any bleeding during pregnancy. In this case you should contact Maternal Fetal Assessment Unit (MFAU) immediately, and only restart aspirin after a doctor has advised you to. MFAU: 020 3447 9400, extension 2. 

Do not take aspirin if you: 

  • Are allergic to aspirin or any other NSAIDs e.g. ibuprofen.
  • Have been advised previously not to take aspirin or other NSAIDs.
  • Have had a stomach ulcer or any other problems with ulcers in the past.
  • Have asthma and it worsens when you take aspirin or any other NSAID.
  • Have severe asthma.
  • Have gout or have had it in the past.
  • Have a bleeding disorder eg. thrombophilia.
  • Are already taking an anticoagulant, unless you have been advised that you can take aspirin.

Please tell your doctor, midwife or general practitioner (GP) if you have met any of the conditions above.

What are the side effects of aspirin?

Aspirin may cause indigestion, so it is best to be taken with food. Avoid taking it on an empty stomach. Other possible side effects include an allergic or hypersensitivity reaction. Seek urgent medical help if you experience any serious side effects such as wheezing, swelling of the lips, face or body or any other effects of an allergic reaction.  

Taking aspirin is not considered to increase the risk of miscarriage, placental abruption (bleeding behind the placenta) or postpartum haemorrhage (heavy bleeding after giving birth) when it is started before 20 weeks.

Is aspirin safe for me and my baby?

There is no evidence that taking aspirin in pregnancy will harm your baby. It is recommended nationally1 for women who are at risk of getting pre-eclampsia in pregnancy. When being used to prevent pre-eclampsia, aspirin must be prescribed. It is not licensed to be given over-the-counter. 

Aspirin can help reduce the risk of complications associated with pre-eclampsia such as: 

  • Pre-term delivery
  • Low birth weight
  • Stillbirth

Who will advise me and prescribe aspirin for me?

Your doctor or GP may advise you to start aspirin and are able to prescribe this for you. 

Your midwife will give you the first two weeks supply of aspirin. Your midwife will send a letter to your GP requesting that they prescribe aspirin for the rest of your pregnancy until 36 weeks. 

You are also entitled to free prescriptions during the pregnancy. Your midwife should complete an FW8 exemption form for you. Please ask your midwife if you haven’t been sent an exemption form.

More information about pre-eclampsia

What is pre-eclampsia?

Pre-eclampsia is a condition that typically develops after 20 weeks of pregnancy, and may affect you, your baby or both. Pre-eclampsia affects between two to eight per cent of pregnant women and can occur in any pregnancy. It is usually diagnosed by a combination of raised blood pressure and protein in your urine or abnormal blood tests. Common symptoms can include a strong frontal headache, very swollen legs/feet, and visual disturbances. 

Can pre-eclampsia be prevented?

If you are found to be at a higher risk for developing pre-eclampsia, taking a low dose of aspirin can reduce your risk of developing early pre-term (<32weeks) pre-eclampsia by about 90 per cent and pre-term (<37weeks) pre-eclampsia by about 60 per cent2.

Why have I been advised to take aspirin during my pregnancy?

Your doctor, midwife, sonographer or GP may advise you to take low dose aspirin if you have any one of the following risk factors:

  • Hypertension (high blood pressure) or pre-eclampsia during a previous pregnancy
  • If you have chronic hypertension (high blood pressure before becoming pregnant)
  • Chronic kidney disease
  • Type one or two diabetes
  • Autoimmune disease such as systemic lupus erythematosus or antiphospholipid syndrome
  • Placental testing confirming problems with your placenta in a previous pregnancy
  • If you have had the first trimester screening for pre-eclampsia and you were found to be at high risk of pre-term pre-eclampsia (have a positive result).

Or if you have at least two of the following risk factors:

  • You’ve never had a baby before
  • You are aged 40 years or older
  • Your last pregnancy was more than ten years ago
  • You have a BMI (body mass index) of 35kg/m2 or more
  • You have a family history of pre-eclampsia
  • You are expecting more than one baby

What is first trimester screening for pre-eclampsia and how do I know if I had it?

At UCLH (University College London Hospitals NHS Foundation Trust), we offer all pregnant women screening for pre-eclampsia at the first trimester scan, developed by the Fetal Medicine Foundation3. Screening is based on maternal demographics together with:

  • An assessment of physical measurements, such as your blood pressure, the resistance in the blood flow through your uterine arteries (which supply the growing uterus) on ultrasound assessment and
  • Measurement of a hormone in your blood called pregnancy-associated placental protein (PAPP-A). This hormone is measured from the blood sample that is taken routinely in all women who have accepted to have combined screening for chromosomal abnormalities including Down’s, Edward’s or Patau’s syndrome.

The screening result gives a risk ratio of developing pre-eclampsia. If this risk is higher than 1 in 100, you have ‘screened positive’ and are deemed to be at a higher risk of developing pre-eclampsia. We will offer you increased monitoring in the pregnancy. You will be recommended to take aspirin. Taking aspirin significantly reduces your chances of developing pre-eclampsia. 

Screening is not a diagnostic test. If you screen positive, it does not mean that you will definitely develop pre-eclampsia. Similarly, there may be a small number of women who develop pre-eclampsia even though their screening is low risk.
If you decide not to have the combined screening for chromosomal abnormalities, you can still choose to have blood taken for the pre-eclampsia screening alone. This may be informative as if you screen positive, we can recommend starting aspirin at the appropriate time in your pregnancy. If you have the pre-eclampsia screening, you will receive a message on your MyChart app with your result soon after your first trimester scan.

I would like to read more on pre-eclampsia and on aspirin. Are there any websites you would advise?

Royal College of Obstetricians and Gynaecologists Pre-eclampsia patient information leaflet: 

Best use of Medicines in Pregnancy website:

NHS website:

Action on pre-eclampsia website:

Tommy’s website:

Who can I contact if I would like further information?

For more information, please contact the midwifery team by email at


  1. National Institute for Health and Care Excellence (NICE). Hypertension in pregnancy: diagnosis and management (NG133) 2023.
  2. Rolnik DL, Wright D, Poon LC, O'Gorman N, Syngelaki A, de Paco Matallana C, Akolekar R, Cicero S, Janga D, Singh M, Molina FS, Persico N, Jani JC, Plasencia W, Papaioannou G, Tenenbaum-Gavish K, Meiri H, Gizurarson S, Maclagan K, Nicolaides KH. Aspirin versus placebo in pregnancies at high risk for preterm preeclampsia. N Engl J Med 2017; 377: 613-622.
  3. The Fetal Medicine Foundation – Assessment of risk for preeclampsia (PE).

Page last updated: 15 May 2024

Review due: 01 May 2025