A Study of Nipocalimab or Intravenous Immunoglobulin (IVIG) in Pregnancies At Risk of Fetal and Neonatal Alloimmune Thrombocytopenia (FNAIT)

Inclusion Criteria:

• Pregnant and an estimated gestational age from week 13 to 18 at visit 1

• Has a history of greater than or equal to (>=) 1 prior pregnancy with FNAIT based onmedical records including: a) neonatal platelet count less than (<) 150*10^9/Literwith no fetal/neonatal intracranial hemorrhage (ICH) or severe fetal/neonatalhemorrhage (standard-risk) OR b) fetus/neonate with ICH or severe hemorrhage in afetus/neonate (high-risk)

• Current pregnancy with presence of maternal anti-HPA-1a and/or anti-HPA-5balloantibody and positive fetal HPA-1a and/or HPA-5b genotype as confirmed bycell-free fetal DNA in maternal blood

• Health status considered stable by the investigator based on physical examination,medical history, vital signs, 12-lead electrocardiogram (ECG), and clinicallaboratory tests performed at screening

• For maternal participant and neonate/infant, willing to forego participation inanother clinical study of an investigational therapy until the last follow-up visit

Exclusion Criteria:

• Currently pregnant with multiple gestations (twins or more)

• History of severe preeclampsia in a previous pregnancy

• History of myocardial infarction, unstable ischemic heart disease, or stroke

• Known allergies, hypersensitivity, or intolerance to nipocalimab or its excipients,to IVIG or to prednisone

• Has any confirmed or suspected clinical immunodeficiency syndrome or has a familyhistory of congenital or hereditary immunodeficiency unless confirmed absent in theparticipant