What is the evidence for aspirin and heparin in recurrent pregnancy loss?

The answer depends entirely on whether antiphospholipid syndrome is present. In confirmed obstetric APS, low-dose aspirin with prophylactic heparin or LMWH is supported. ASRM (2026) recommends low-dose aspirin before conception, with prophylactic heparin initiated at clinical or laboratory evidence of pregnancy. Patients with a history of thrombotic events and APS should receive therapeutic anticoagulation. Given changing testing and treatment guidance, ASRM recommends referral to a haematologist or rheumatologist with APS expertise for those with confirmed persistent moderate-to-high titres and positive lupus anticoagulant. Outside APS, ASRM states plainly that anticoagulants are not recommended for RPL with hereditary thrombophilia or unexplained RPL, on the basis of high-quality evidence showing no benefit on live birth or miscarriage rate. The supporting trials: ALIFE found neither LMWH with aspirin nor aspirin alone improved live birth in unexplained RPL. A randomised trial in women with inherited thrombophilia found 72% versus 71% live birth, treated versus untreated. A 2022 meta-analysis of seven randomised studies found no benefit of LMWH or LMWH plus aspirin on miscarriage, live birth or pre-eclampsia risk. Empirical anticoagulation remains widely prescribed, often at patient request. Declining is harder than prescribing, and the conversation is easier when the evidence is stated as high-quality and negative rather than as clinical preference.