Placebo will be administered intravenously.

Fetus/neonate with outcome of death will be reported.

Platelet count at birth <10×10^9/L in a neonate will be reported.

Platelet count at birth <30×10^9/L in a neonate will be reported.

Platelet count at birth <50×10^9/L in a neonate will be reported.

Platelet count at birth <150×10^9/L in a neonate will be reported.

Nadir platelet count in a neonate will be reported.

Neonate(s) who require at least one platelet transfusion(s) will be reported.

Number of Platelet transfusion(s) per neonate will be reported.

Number of donor exposures for neonates who received platelet transfusion(s) will be reported.

Neonate/Fetus With adjudicated severe bleeding will be reported.

Neonates with IVIG for the treatment of thrombocytopenia will be reported.

Maternal participants with a TEAE will be reported. An adverse event (AE) is any untoward medical occurrence in a participant participating in a clinical study that does not necessarily have a causal relationship with the intervention under study. TEAEs are defined as AEs with onset or worsening on or after date of first dose of study treatment.

Maternal participants with SAE will be reported. An adverse event (AE) is any untoward medical occurrence in a participant participating in a clinical study that does not necessarily have a causal relationship with the intervention under study. SAE is any untoward medical occurrence that at any dose that results in death, is life-threatening, requires inpatient hospitalization/prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect and is medically important.

Maternal participants with an AESI will be reported. An adverse event (AE) is any untoward medical occurrence in a participant participating in a clinical study that does not necessarily have a causal relationship with the intervention under study. AESIs are considered as infections that are severe, hypoalbuminemia, deep vein thrombosis and/or pulmonary embolism, and clinically significant bleeding.

Maternal participants with TEAE leading to discontinuation of study intervention will be reported.

Neonatal/infant participants with a TEAE will be reported. An adverse event (AE) is any untoward medical occurrence in a participant participating in a clinical study that does not necessarily have a causal relationship with the intervention under study. TEAEs are defined as AEs with onset or worsening on or after date of first dose of study treatment.

Neonatal/infant participants with SAE will be reported. An adverse event (AE) is any untoward medical occurrence in a participant participating in a clinical study that does not necessarily have a causal relationship with the intervention under study. An SAE is any untoward medical occurrence that at any dose that results in death, is life-threatening, requires inpatient hospitalization or prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect and is medically Important.

Neonatal/infant participants with AESI will be reported. An adverse event (AE) is any untoward medical occurrence in a participant participating in a clinical study that does not necessarily have a causal relationship with the intervention under study. AESIs are considered as: In infants- clinically significant mortalities in fetus/neonates due to maternal infections, and hypogammaglobulinemia.

Fetus/Neonate with TEAE of Bleeding will be reported. An adverse event (AE) is any untoward medical occurrence in a participant participating in a clinical study that does not necessarily have a causal relationship with the intervention under study. Treatment-emergent AEs are defined as AEs with onset or worsening on or after date of first dose of study treatment.

Neonate with TEAE of Infection will be reported. An AE is any untoward medical occurrence in a participant participating in a clinical study that does not necessarily have a causal relationship with the intervention under study. Treatment-emergent AEs are defined as AEs with onset or worsening on or after date of first dose of study treatment.

The Bayley Scales of Infant and Toddler Development include a set of individually administered developmental scales designed to measure current developmental functioning in infants and toddlers up to 42 months of age in the areas of cognition, language, motor skills, social-emotional, and adaptive behavior, with age adjusted for prematurity. The cognition, language, motor skills scales are directly administered to the infant, while social-emotional, and adaptive behavior scales are caregiver questionnaires. The scores are standardized using norm reference samples with representative demographics and age adjusted for prematurity.

Maternal participants with antibodies to nipocalimab including neutralizing antibodies in maternal serum during pregnancy and postpartum will be reported.