Low Dose Aspirin 75 to 150mg in Pregnancy

Aspirin is known as an NSAID (a non-steroidal anti-inflammatory drug). Aspirin is often used to treat pain, fever, inflammation or prevent clot formation.

Low Dose Aspirin (75 to 150mg) in PregnancyTo view a PDF you may need to download Adobe Reader.

What is aspirin?

Aspirin is known as an NSAID (a non-steroidal anti-inflammatory drug). Aspirin is often used to treat pain, fever, inflammation or prevent clot formation.

There is evidence that some women might benefit from taking a low dose of aspirin once a day.  This can help improve the function and blood flow of your placenta which provides your baby with oxygen and nutrients during your pregnancy.

Why have I been offered aspirin during my pregnancy?

Some women have factors that might mean they could have a higher chance of:

  • Developing hypertension (high blood pressure) and pre-eclampsia (a serious condition which usually presents as high blood pressure and protein in the urine)
  • Giving birth to your baby prematurely (before 37 weeks)
  • Fetal growth restriction (when the baby is smaller than usual due to not growing at a normal rate in the womb)

Studies show that taking a low dose of aspirin each day:

  • Reduces the rates of high blood pressure and pre-eclampsia by around 60%
  • Reduces likelihood of preterm birth by 11%
  • Reduces the likelihood that the baby will experience growth restriction – although by how much is influenced significantly by other factors, such as smoking

You have been advised to take a low dose of aspirin during your pregnancy to reduce your personal risk of developing one or all of these.  Having an ‘at risk’ factor does not mean you will definitely develop the complication, but it does mean you might benefit from taking aspirin.

How and when do I take aspirin?

It is extremely important that, if you are advised and you choose to take aspirin, you take this daily.  We strongly encourage you to keep close track and make sure you take this daily (or as close to daily as possible) to maximise the benefits.  Taking aspirin occasionally will not give the same protection against complications.

We recommend you take aspirin 150mg once a day, starting in the first trimester from 12 weeks and stopping at 36 weeks (around 36+0). It is best to take in the evening either with or just after food.

If you think you may be experiencing signs that labour is starting, you should stop taking your aspirin until this is checked.  Low dose aspirin does not increase your risk of bleeding during labour.  We advise you stop at 36 weeks as, after this, continuing to take aspirin does not seem to give the same benefits.

What are the side effects of aspirin?

Mild indigestion is a common side effect.  This affects around 1 in 100 people.  To help you think about how likely this might be for you:

  • 1:100 chance of experiencing this side effect
  • This could be about one of all the people who live on your street
  • This is a 1% chance
  • You have a 99% chance of not having this side effect

If you take aspirin either with or just after food, it will be less likely to upset your stomach. If you also take indigestion remedies, take them at least two hours before or after you take your aspirin.

As with any medicine, you should seek urgent medical assistance if you experience serious side effects such as:

  • Wheezing
  • Swelling of the lips, face or body
  • Rashes
  • Severe stomach pains
  • Vomiting blood
  • Passing blood in your poo

There is no evidence to suggest low dose aspirin causes any increase in vaginal bleeding during pregnancy or at the time of birth.

If you have any questions or concerns about taking low dose aspirin please speak to your obstetrician, GP or midwife.


Please tell your obstetrician, midwife or GP if you are allergic to aspirin (or other NSAIDS).  Also make sure your team are aware if you have severe asthma (requiring hospital treatment), chronic kidney problems, stomach ulcers or have been previously advised not to take aspirin or other NSAIDs.

What can I do to help?

If you smoke it is very important that you think about stopping.

Smoking is associated with the highest chances of having complications during pregnancy.  It often affects the placental function and your baby’s growth and may increase the chance that your baby becomes unwell.

We know how difficult it can be to stop smoking. Please speak to any of our team about how we can support you in a way that works for you. We have a support team who are experienced in helping families with smoking, which is friendly and non-judgemental.  Nicotine Replacement Therapy (NRT) is safe in pregnancy and we can help you to access this if you like.