Preventing prematurity: spotlight on Aspirin and preeclampsia

Preeclampsia, a disorder characterized by protein in the urine and high blood pressure (although there are some variants where blood pressure is normal) is a risk factor for premature delivery. The earlier a mom develops this condition the greater the risks. Preeclampsia is typically divided into mild and severe based on the amount of protein in the urine, the blood pressure reading, and other factors such as symptoms (like headache or abdominal pain), the results of lab tests, or ultrasound results (such as growth restriction of the baby or amount of amniotic fluid).

Severe preeclampsia requires delivery. This is a very serious condition – preeclampsia is resposible for 17% of maternal deaths in the United States. However, in some circumstances if mom is well enough and baby is premature enough, delivery can be stalled for 48 hours while steroids are given to mature the lungs.

Preeclampsia affects 5-8%of women and about 0.42% of all pregnant women need to be delivered before 34 weeks because of severe preeclampsia.  As there are about 4 million births every year in the United States, preeclampsia results in 16,800 premature babies born before 34 weeks.

Preventing preeclampsia is a major goal. We know that high blood pressure, diabetes, kidney disease, and obesity are all factors. Having a previous pregnancy complicated by  preeclampsia, growth restriction, or abruption also increases the risk. How great your risk of having another pregnancy with preeclampsia will depend on all these factors as well as how early you experienced pregnancy complications in your previous pregnancy.

But there is hope!

A  new study, a meta-analysis (a study that looks at a lot of other studies and tries to come up with the best summary) has looked at the role of Aspirin at preventing preeclampsia for women at risk. A preeclampsia is a condition that seems to come from blood vessels problems in the placenta, Aspirin is attractive because it decreases the risk of blood clots in abnormal vessels and may also help blood vessels to open up (in preeclampsia blood vessels in the placenta are often too small or in spasm).

So how did Aspirin fare in this study published in Obstetrics and Gynecology (August 2010)?

Taking a low dose of Aspirin (50 – 100 mg) every day at or before 16 weeks for women at high risk for preeclampsia significantly reduced the risk of developing the disease: among controls who didn’t take Aspirin the risk of preeclampsia was 21.3% and among Aspirin takers it was 9.3%. Starting Aspirin after 16 weeks was not effective.

But it is preventing severe preeclampsia that we really care about, because that is what leads to delivery. Starting Aspirin at or before 16 weeks reduced the risk of severe preeclampsia from 15% to 0.7%. Again, starting it after 16 weeks didn’t seem to do too much, which makes sense because for Aspirin to work it probably needs to be on board while the placenta is forming, which is the first trimester.

Aspirin at or before 16 weeks also reduced the need for premature delivery overall in this high risk group of women, from 16.9% to 3.5%, as well as the risk of severe growth restriction, from 23.0% to 10.7%.

The problem with this study is the number of women who took low-dose Aspirin before 16 weeks was on the low side, so it is possible a larger study looking only at this sub group of women may find different results.

Not everyone knows they are at high risk for preeclampsia, but many do. If you have high-blood pressure, kidney disease, diabetes, or had problems in your previous pregnancy (such as preeclampsia, high blood pressure, or growth restriction) having a conversation with your doctor about prevention strategies for severe preeclampsia is a good idea. Only your doctor can determine whether or not Aspirin is right for you, but it should definitely be part of the conversation. As Aspirin needs to be started at or before 16 weeks the best time to start the conversation is before you get pregnant or as soon as you have a positive pregnancy test.

This blog is not intended as individual medical advice. Do not start any therapy or medication without the specific approval of your own medical doctor.

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