The primary purpose of the study is to characterize the current standard of care, clinical course, and outcomes of pregnant women and their offspring at high risk for early onset severe hemolytic disease of the fetus and newborn (EOS-HDFN).

The outcomes of interest will be assessed from the information collected on the standard of care treatment for EOS-HDFN in pregnant women and their offspring from current pregnancy.

Pregnant female participants must be ≥18 years of age with an estimated Gestational Age of ≥ 8 weeks; not currently pregnant with multiples (twins or more); and no other clinically relevant abnormalities currently or in their history that the Investigator would deem them ineligible to participate.

Participants must have an obstetrical history of severe fetal anemia, hydrops, or stillbirth related to hemolytic disease of the fetus and newborn, have alloantibody titers for anti-D ≥32 or anti-Kell titers ≥4, and be currently pregnant with an antigen-positive fetus. Eligible women may enter the study at any time during the current pregnancy prior to delivery.