Fluorescently labeled mAb accumulates at the placental–fetal interface. To assess maternally administered Ab biodistribution, conjugated Ab was administered intravenously (IV) on day 15 or 16 of gestation to B6 mice, then 2–3 d later tissues were prepared for whole body imaging using the cryo-macrotome. (A) Background fluorescence levels in a pregnant dam (n = 1) not injected with conjugated Ab. (B) Accumulation of fluorescently labeled UB-621 Ab in a pregnant dam (n = 1) 2 d following IV administration. (C) Accumulation of fluorescently labeled Ab following administration to the pregnant dam (n = 1) in a subset (showing 3 of 6 pups) of harvested conceptuses from the murine uterus, with maternal and fetal layers removed as indicated.