Background In the absence of a defining history, aPLs are of uncertain clinical significance.

Aim To compare obstetric outcomes between women with aPL and APS.

Study design Retrospective cohort study of women with known aPL attending the Obstetric Medicine Clinic, 2005-2011. Women were classified as aPL or obstetric APS (by 2006 classification criteria). Multiple pregnancies, APS diagnosed post-partum, thrombotic APS and secondary APS were excluded.

Results Of 161 pregnancies in 112 women, 80 (48.5%) were aPL and 81 (51.5%) were obstetric APS. There were no significant differences in baseline characteristics.

The incidence of pre-eclampsia (PET) was 6.2% (n=10), early PET 3.7% (n=6) and abruption 3.1% (n=5). Low molecular weight heparin (LMWH) was not protective against SGA (OR 0.92; 95% CI 0.34-2.70), early PET (OR 0.45; 0.09-2.33) or abruption (OR 0.69; 0.11-4.28). In women with aPL the risk of SGA (OR 0.20; 0.06-0.62) was lower compared to APS. There were similar trends in the risk of early PET (OR 0.19; 0.02-1.69) and abruption (OR 0.24; 0.03-2.23). These associations persisted following adjustment.

Conclusion Women with aPL have infants with higher birthweight and better obstetric outcomes that were not improved by LMWH. LMWH is not indicated in aPL pregnancies.