Pregnant and an estimated gestational age (GA) from week 13\* to 18 at visit 1
\*Randomization for high-risk FNAIT participants to occur at GA Week 12
Has a history of greater than or equal to (\>=) 1 prior pregnancy with FNAIT based on medical records including: a) neonatal platelet count less than (\<) 150\*10\^9/Liter with no fetal/neonatal intracranial hemorrhage (ICH) or severe fetal/neonatal hemorrhage (standard-risk) OR b) fetus/neonate with ICH or severe hemorrhage in a fetus/neonate (high-risk)
Current pregnancy with presence of maternal anti-HPA-1a and/or anti-HPA-5b alloantibody and positive fetal HPA-1a and/or HPA-5b genotype as confirmed by cell-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 clinical laboratory tests performed at screening
For maternal participant and neonate/infant, willing to forego participation in another clinical study of an investigational therapy until the last follow-up visit
You may not be if
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 family history of congenital or hereditary immunodeficiency unless confirmed absent in the participant
Clareo Health | A Study of Nipocalimab or Intravenous Immunoglobulin (IVIG) in Pregnancies At Risk of Fetal and Neonatal Alloimmune Thrombocytopenia (FNAIT)
