Scambi C, Ugolini S, Tonello M, et al. - Because higher plasma complement activation product levels have been identified in antiphospholipid antibody-positive women with adverse pregnancy outcomes and C4d complement component deposition has been seen in the placentas of women with antiphospholipid syndrome (APS), researchers investigated if complement activation is implicated in APS pregnancy complications. Participants were 43 APS non-pregnant patients and 17 pregnant APS women. For comparison of results, they included 16 healthy non-pregnant women and 8 healthy pregnant women, respectively. The non-pregnant APS patients with past thrombosis ± pregnancy morbidity and the pregnant APS women with adverse outcomes had significantly higher mean plasma C5a and C5b-9 levels. Similarly, significantly higher C5b-9 quantities were identified in the adverse-pregnancy-outcome-placenta vs in those related to a favorable outcome. Overall, the more severe subset of APS patients and only the adverse-pregnancy-outcome-APS women were found to have significant complement activation. If the lower CD46, CD55 and CD59 expressions in the APS placentas stay restricted to only high risk APS patients will be clarified in further investigations.