Financial Disclosure: Dr. Moise receives fees paid on his behalf to Dell Medical School - UT Austin for consultation with the genetics company BillionToOne, Inc. This week we're trekking on through more details about alloimmunization and HDFN in the setting of lab studies and specific testing. Dr. Moise discusses the timing intervals for maternal antibody screenings, defines a critical titer, and then we get into the juicy part.....who's the daddy?! We talk about the paternal zygosity as it applies to alloimmunization as well as cffDNA to find out baby's antigen status.