A Study of Nipocalimab in Pregnancies at Risk for Severe Hemolytic Disease of the Fetus and Newborn (HDFN) (AZALEA)

Inclusion Criteria: Pregnant and an estimated gestational age (GA) (based on ultrasound dating) from Week 13^0/7 to Week 16^6/7 at randomization History of severe Hemolytic Disease of the Fetus and Newborn (HDFN) in a prior pregnancy defined as: documented fetal anemia, or received greater than or equal to (>=)1 IUT as a result of HDFN or fetal loss or neonatal death as a result of HDFN, with maternal alloantibody titers for Rhesus antigen D protein (RhD), Kell, Kell Rhesus antigen C protein (Rhc), Rhesus antigen E protein (RhE), or RhC antigen above the critical levels (anti-Kell >=4; other >=16) and evidence of an antigen-positive fetus During the current pregnancy, presence of maternal alloantibody to RhD, Rhc, RhE, or RhC antigen with titers above the critical level (anti-Kell >= 4; other >=16) based on the designated central lab results at screening Evidence of antigen-positivity corresponding to the current maternal alloantibody (RhD, Kell, Rhc, RhE, or RhC) confirmed by non-invasive antigen cell-free fetal DNA (cffDNA) performed at the central laboratory. Have screening laboratory values within the study protocol-specified parameters: a) albumin, >=2.6 grams (g) per deciliter (g/dL), international system (SI): >=26 gram per liter (g/L); b) alanine transaminase (AST) less than or equal to (<=) 2 × upper limit of normal (ULN); c) alanine transaminase (ALT) <=2 × ULN d) creatinine <=0.8 milligrams per deciliter (mg/dL), SI: <=70.7 micromole per liter (μmol/L), and Serum total immunoglobulins G (IgG) ≥ 600 mg/dL SI: >=6 g/L Otherwise healthy on the basis of physical examination, medical history, vital signs, 12-lead ECG, and clinical laboratory tests performed at screening. Exclusion Criteria: Currently pregnant with a multiple gestation (twins or more) Evidence of fetal anemia prior to randomization in the current pregnancy Current uncontrolled hypertension History of myocardial infarction, unstable ischemic heart disease, or stroke Has any confirmed or suspected clinical immunodeficiency syndrome or has a family history of congenital or hereditary immunodeficiency unless confirmed absent in the participant Has inflammatory or autoimmune diseases requiring immunosuppressive therapies that may jeopardize the safety of the participant Currently has a malignancy or has a history of malignancy within 3 years before screening (with the exception of localized basal cell carcinoma and/or squamous cell carcinoma skin cancer that has been adequately treated with no evidence of recurrence for at least 3 months Is currently receiving systemic corticosteroids or other immunosuppressants for disorders unrelated to the pregnancy Has received or planning to receive plasmapheresis, immunoadsorption therapy, intravenous immunoglobulin (IVIg), or any immunoglobulin (Ig)G fragment crystallizable (Fc)-related protein therapeutics during the current pregnancy Has a severe infection including opportunistic infections Presence of abnormal (protocol-specified) hematologic laboratory values during screening History of severe preeclampsia prior to GA Week 34 or severe fetal growth restriction (estimated fetal weight <3rd percentile, based on local fetal growth normative standards) in a previous pregnancy