Prenatal screening for ATM. (1) This tool is not a replacement for referral to genetic counseling, which may happen at any time in this pathway. Genetic counseling provides guidance for genetic testing and management options for families with pregnancies at risk for severe forms of thalassemia. (2) The sensitivity and specificity are not definitive, and not all carriers will be detected by this screening. (3) The American College of Obstetricians and Gynecologists recommends that all pregnant women have a CBC with assessment of MCV. (4) Rare mutations, such as nondeletional α-thalassemia and others, may not be captured in this algorithm. In high-risk cases, or where Hb electrophoresis is abnormal, consultation with a genetic counselor and/or hematologist is recommended. (5) The presence of HbA2 > 3.5 does not exclude a coexisting α⁰-thalassemia trait. In individuals of Southeast Asian, Filipino, or Chinese descent who have microcytic hypochromic anemia, perform α-globin gene deletion and common variant studies irrespective of HbA2 level. CBC, complete blood count; CVS, chorionic villus sampling; HPLC, high-performance liquid chromatography; MCA, middle cerebral artery; MCH, mean corpuscular hemoglobin; MCV, mean corpuscular volume; MoM, multiples of the median; PCR, polymerase chain reaction; PSV, peak systolic velocity; PUBS, percutaneous umbilical blood sampling. Adapted with permission from the University of California, San Francisco hemoglobinopathy screening algorithm.