Defective endovascular trophoblast invasion in primary antiphospholipid antibody syndrome-associated early pregnancy failure

Background: Primary antiphospholipid antibody syndrome (PAPS) is an established cause of recurrent pregnancy loss, traditionally presumed to be due to 'intraplacental thromboses'. This study examines products of conception (POC) from early pregnancy failures to investigate the mechanism of pregnancy loss. Methods: POC from patients attending a recurrent miscarriage clinic and from terminations of pregnancy for non-medical reasons were examined histologically with particular regard to the presence or absence of vascular or intervillous thromboses and decidual endovascular trophoblast invasion. Results: There were 31 PAPS-positive, 50 PAPS-negative, 34 aneuploid and 20 control cases at 6-14 weeks gestation. Villous morphology and frequency of intervillous thrombosis were not different among groups. Normal intradecidual endovascular trophoblast invasion was identified significantly less frequently in PAPS+ cases (24%), compared with controls (75%), aneuploid (53%), or PAPS-cases (61%; Z = -3.0, P<0.01). In all cases there was apparently normal interstitial extravillous trophoblast invasion. Conclusions: Defective decidual endovascular trophoblast invasion, rather than excessive intervillous thrombosis, is the most frequent histological abnormality in PAPS+ associated early pregnancy loss. Furthermore, endovascular trophoblast invasion is not significantly reduced in the majority of fetal aneuploidy-associated pregnancy failures.