Does low dose aspirin reduce the risk of miscarriage?

By , 3 April 2014

Does low dose aspirin reduce the risk of miscarriage?

According to an RCT published in The Lancet this week - maybe...

Low-dose (75-100mg) daily aspirin ("LDA"), commenced before 16 weeks, has been shown in high-powered studies to reduce the risk of some adverse pregnancy outcomes such as pre-eclampsia, fetal growth restriction, and preterm birth.  The effect is strongest in high-risk women (viz. women who have suffered such adverse events in previous pregnancies; see Villa et al, BJOG 2013 and Roberge et al Ultrasound O&G 2013).  As often happens in medicine, "indication creep" means that we become tempted to prescribe these proven therapies for indications in which they are unproven.  Recurrent miscarriage or recurrent pregnancy loss ("RPL", defined as three or more consecutive pregnancies ending in miscarriage before 20 weeks) causes immeasurable anguish to couples, and it is normal to seek out ways of mitigating against future pregnancy loss.  Interestingly, LDA coupled with low dose heparin has been shown to reduce the rate of subsequent miscarriage in women with RPL who also have antiphospholipid syndrome; whereas this recipe has no effect in women with RPL in the absence of antiphospholipid syndrome (Kaandorp et al Cochrane 2009).

The use of LDA in women without RPL (that is, one or two miscarriages only) has found mixed results with small, unpowered studies previously.  The authors of this most recent, large, placebo-controlled RCT (dubbed the "EAGeR study") sought to scrutinise this relationship more clearly.  They studied the effect of commencing such women on LDA before conception, and found no improvement in livebirth or miscarriage rates for women who had "one or two" previous miscarriages, and concluded that routine LDA should not be used in this group.  Interestingly, however, their data did reveal a statistically significant improvement in pregnancy and livebirth rates in a group of women who had one previous miscarriage, before 20 weeks, within the last year.  Hmm... tough to explain the mechanism there, and perhaps it's a statistical anomaly ("Lies, damned lies, and statistics"), but certainly that little chestnut requires more research.  Miscarriage has a very complex group of causes, and there's no biologically plausible way that aspirin would improve many of them (such as chromosomal problems).

So, bottom line, LDA shouldn't be used indiscriminately with the hope of improving livebirth rates - we have good evidence for particular populations of women who benefit, and quality evidence to refute benefit in other populations.  This study adds to this knowledge.  

PS- I often get raised eyebrows when discussing aspirin use in pregnancy ("isn't that harmful?") - there is extensive evidence for the safety of low-dose aspirin when suitably prescribed in pregnancy (James et al O&G Survey 2008).

 

Does low dose aspirin reduce the risk of miscarriage?
 

About Dr David Moore

Does low dose aspirin reduce the risk of miscarriage?

David is a Fellow of the Royal Australian and New Zealand College of Obstetricians and Gynaecologists, and undertook his specialist training in Queensland.  He is highly skilled in the management of complex and high-risk pregnancies, and has special training in minimally-invasive surgery, endometriosis, pelvic floor and incontinence surgery.  David has completed a Master of Reproductive Medicine and is skilled in the assessment and management of fertility problems, and can offer the full range of assisted reproductive treatments.  He is a Senior Lecturer with The University of Queensland Medical School, and has published both medical journal and textbook contributions.

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