Considering the 93 patients (71 APS and 22 aPL carriers) with low preconception C3 and/or C4 and comparing them to patients with normal complement level, a significantly higher prevalence of pregnancy losses was observed (p = 0.008) as well as a higher prevalence of preterm live birth from the 37th week of gestation and earlier (Table 2). Here, C4A is linked to autoimmune polyendocrinopathy.