Preventing pre-eclampsia

Many conditions that cause problems in the second half of pregnancy have their origins much earlier. Recent research has shown that several major pregnancy complications, including pre-eclampsia, can be lessened or prevented by treatment from the first trimester.

Pre-eclampsia is a particularly exciting area of prevention as it is a serious condition that cannot be cured except by birth, has significant risks for both mother and baby, and is now known to be safely reduced by around 60% with a simple daily dose of aspirin (at night).

What causes pre-eclampsia?

In summary, this is not entirely clear, and there are probably multiple different causes of pre-eclampsia.

Research suggests in many cases early placental development is less than normal with smaller active area which is not a problem early on, but as your baby grows in the later part of pregnancy the placenta is not able to easily support this growth. This causes the placenta to release hormones that cause the maternal symptoms (swelling, headache, visual changes, pain in the top right of the tummy) and clinical signs (high blood pressure, fast reflexes, liver pain, a small baby on ultrasound or one with abnormal blood flows) of pre-eclampsia.

Other women develop pre-eclampsia because pre-existing medical disease affects normal placental function or because their cardiovascular reserve is not enough to supply the growing placenta which requires a lot of energy to support- your heart is doing about 50% more work than normal by half-way through your pregnancy.

Who gets pre-eclampsia?

Women can be assessed for risk of pre-eclampsia one of two ways; on the presence of risk factors or with a screening test (blood test, blood pressure measurement and ultrasound of uterine artery).

Risk-factor based assessment results in a reasonable proportion of pregnant women taking preventative aspirin, but as aspirin is safe, this is not an issue.

Your caregiver will discuss this with you and you can also read the fact sheet on aspirin for preventing pre-eclampsia to learn more about specific risk factors.

Complicating matters, many women who screen positive on risk factors never develop pre-eclampsia and some women who appear to have no risk factors develop it. The screening test, if performed, can help guide who is most likely to develop early pre-eclampsia (the kind that has the highest chance of harm for mum and baby) and would benefit the most from aspirin.

Why do I need to start aspirin early?

Aspirin is started early to help the placenta grow and continue to develop optimally. This is before 16 weeks although there is a lesser degree of benefit if started later.

Is aspirin safe?

In short, yes. A very large trial (ASPRE) was able to demonstrate the safety of aspirin at 150mg in pregnant women for mothers and their babies and that it successfully reduced the incidence of severe early pre-eclampsia, the kind most associated with harm to mother and baby. Many other well conducted studies have drawn similar conclusions.

What else reduces my risk of pre-eclampsia?

There are other things you can do to reduce your chance of developing pre-eclampsia. These include maintaining a healthy BMI, keeping any chronic medical conditions well controlled and taking a calcium supplement or having a calcium rich diet.

Should I do the pre-eclampsia screening test?

This is an individual decision. The test is a private test and not entirely covered by Medicare. It is however able to more precisely target low dose aspirin to at risk women that risk-factor screening can miss. It is also reasonable to take low dose aspirin (150mg, half a standard tablet) at night instead.

Women who screen ‘high risk’ on the screening test are also offered additional scans for baby’s growth as this risk is also increased in screen-positive women.

Why take aspirin at night?

Interestingly, there is good data which shows that aspirin taken at night is much more effective than aspirin taken in the morning at preventing pre-eclampsia, even when all else is equivalent.

This is called ‘chronobiology’, a developing field that also has interesting discoveries about the best times to take other routine medications.