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

Open to females ages 18-45

• Pregnant and an estimated gestational age (GA) (based on ultrasound dating) from Week 13⁰/7 to Week 16⁶/7 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