Despite the progressively raising bulk of evidence, available data on C3 and C4 as predictors of adverse obstetric outcome in lupus and APS are not consistent, not yet allowing to draw definite conclusions about the clinical relevance of complement monitoring throughout pregnancy progression in these settings (Chighizola et al., 2020; Nalli et al., 2021). Here, C4A is linked to autoimmune polyendocrinopathy.