Although far from conclusive, the available clinical and histopathological information are consistent with an hypoxic cause for aPL-related fetal loss. In turn, this is due to impairment of the maternal spiral arterial blood flow. To date, there is only one case report of detailed placental and uteroplacental vascular histopathological examination by a recognized expert in this field of pathology. This and the findings provided by the only study to take placental bed biopsies suggest that spiral arterial vasculopathy resulting in placental and fetal hypoxia is the immediate cause of fetal loss in women with aPL syndrome. Data from the large study by Out et al. are consistent with this. The absence of spiral arterial vasculopathy in several studies could be attributed to the fact that the vessels examined were those adherent to the separated placenta, too superficial to necessarily demonstrate the pathological changes. Our future efforts at defining the 'cause' of aPL-related fetal loss must include: (1) meticulous clinical details regarding the timing and nature of pregnancy loss, (2) thorough evaluation of the abortus, (3) examination of the placenta by a pathologist well versed in placental pathology, (4) examination of the placental bed biopsies whenever possible, (5) the cellular biology and biochemistry of maternal-fetal junction, with particular focus on how the cytotrophoblast invades the spiral arteries, and (6) the cellular biology and biochemistry of spiral arterial vasculopathy.