Is Aspirin a Treatment for Recurrent Pregnancy Loss?

Aspirin is in widespread use in recurrent miscarriage, as it is believed to increase blood flow to embryo, and prevent thrombosis in placental vessels, thereby preventing miscarriage. The aim of using aspirin is entirely laudable, to prevent women with recurrent pregnancy losses from suffering additional miscarriages. At the recurrent miscarriage clinic in Tel Hashomer, approximately 40% of new patients have been previously treated empirically with aspirin. Pregnancy itself is a hypercoagulable state associated with increased levels of procoagulant factors, and decreased levels of naturally occurring anticoagulants such as protein S, and microthrombi are a common finding in the placental vasculature of women with recurrent miscarriage.

However, the evidence for using aspirin is limited. There is only one small randomized study of 54 women in which aspirin was compared to placebo in unexplained pregnancy loss. Low dose aspirin was found to be ineffective. There are two metaanalyses of aspirin in antiphospholipid syndrome. Neither found aspirin to confer a significant benefit. There is only one paper which shows an effect in late pregnancy losses, when hereditary thrombophilias have not been excluded. However, all of these results may have been confounded by the failure to assess fetal karyotypic aberrations.

The possibility of side effects such as an increased risk of gastroschisis etc. and the fact that there is no evidence that aspirin is efficacious in treating women with recurrent miscarriage, seem to contraindicate prescribing aspirin in early pregnancy.