Rituximab and pregnancy: Late-onset neutropenia in a 2-month infant whose mother received rituximab 2 weeks prior to childbirth.

Late-onset neutropenia (LON) is a rare adverse event that has not been reported from in utero exposure. We describe a case of LON in an infant, whose mother had neuromyelitis optica and received rituximab in the third trimester due to re-emergence of CD19 B cells. The newborn was born without complications but 2 months later was found to have grade IV neutropenia. No etiology was identified. Neutropenia self-resolved within 1 week. This case emphasizes an unmet need for developing guidelines and protocols to manage in utero rituximab exposure.