Algorithm for the initial biological workup in women with TMA occurring during pregnancy and the postpartum. Different causes of pregnancy-associated TMA are to be ruled in or out (from top to bottom) before the diagnosis of atypical HUS is made. The most likely diagnoses are shown in full colored rectangles. *TMA in pregnancy is diagnosed based on the presence of a platelet count <100 × 10⁹/L, a hemoglobin level <10 g/dL, LDH >1.5 upper limit of normal, undetectable serum haptoglobin, negative direct erythrocyte antiglobulin test, and (1) the presence of schizocytes on blood smear or (2) TMA features in kidney biopsy. **Cutoff proposed by the working group. May vary according to the diagnostic assay used in each expert laboratory. ***These steps are optional and are performed on a case-by-case basis. ALAT, alanine aminotransferase; ASAT, aspartate aminotransferase; BP, blood pressure; GPI, glycoprotein I; HELLP, hemolysis elevated liver enzymes and low platelet count; LPS, lipopolysaccharide; MMACHC, methylmalonic aciduria and homocystinuria type C protein; PCR, polymerase chain reaction; PlGF, placental growth factor; PE/E, preeclampsia/eclampsia; sFlt1, soluble fms-like tyrosine kinase-1; Stx, Shiga toxin; ULN, upper limit of normal; WG, weeks of gestation.