Restricted foetal growth was associated with presence of different immunological features and clinical manifestations, such as low levels of C3 (OR 13.0, p = 0.04) and C4 (OR 20.0, p = 0.02) up to 1-year before conception, as well as presence of aPL during pregnancy (OR 17.3, p = 0.03), concomitant APS diagnosis (OR 13.0, p = 0.04) and previous LN (OR 12.6, p = 0.04). The gene discussed is C3; the disease is autoimmune polyendocrinopathy.