Heparin for APS During Pregnancy

What does the evidence say about heparin for antiphospholipid syndrome during pregnancy?

1. APS is not established by one antibody result alone. It involves a compatible thrombotic or obstetric history plus persistent antiphospholipid antibodies; current 2023 ACR/EULAR criteria are research classification criteria and should not be used as a stand-alone clinical rule for every patient. 1
2. EULAR recommends low-dose aspirin plus prophylactic heparin during pregnancy for criteria obstetric APS with three or more early losses or a fetal loss at or beyond 10 weeks. For prior early severe preeclampsia or placental insufficiency, aspirin alone or combined with heparin is selected by individual risk. 2
3. A meta-analysis of 13 trials and 1,916 participants with APS found low-certainty evidence that heparin, with or without aspirin, increased live birth compared with varied comparators. Heterogeneity was substantial, minor bleeding increased, and preterm birth and fetal growth restriction were not significantly different. 3
4. A Cochrane review of 11 randomized or quasi-randomized studies with 1,672 women found that heparin plus aspirin may increase live birth versus aspirin alone in persistent antiphospholipid antibodies and recurrent pregnancy loss, but the evidence was low certainty and individual trials were generally small. 4
5. A 2026 scoping review of 14 randomized trials found that low-dose aspirin plus low-molecular-weight heparin was associated with higher live birth than other evaluated strategies, but the finding relied on a small, heterogeneous evidence base and was disproportionately driven by one large trial. 5

Is heparin for antiphospholipid syndrome safe in each trimester?

• First trimester. Confirm that the history and persistent antibody pattern support obstetric APS before using an anticoagulant plan. EULAR recommends prophylactic heparin plus low-dose aspirin for specific prior obstetric APS events; prior thrombosis can require a different heparin intensity.
• Second trimester. Continue specialist surveillance for blood pressure, fetal growth, placental function, platelet changes, bruising, or bleeding. Heparin does not remove the risk of preeclampsia, placental insufficiency, pregnancy loss, or thrombosis.
• Third trimester. The obstetric, hematology, and anesthesia teams should set the final-dose, labor, neuraxial-anesthesia, and postpartum plan. Do not change heparin or aspirin timing independently because both clotting and bleeding risks shift near delivery.