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

Eligibility 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:
• 1. documented fetal anemia, or received greater than or equal to (\>=)1 IUT as a result of HDFN or
• 2. 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.
• * 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