Predator-induced defenses are well-known adaptive responses found in many marine and freshwater organisms. These responses usually occur in juveniles or actively growing adults and reduce the ability of a predator to consume its prey. We report a predator-induced response occurring in utero in the viviparid snail Bellamya chinensis (Gray, 1863) that results in significant changes in offspring number, shell size variability of released juveniles, and juvenile shell organic content. Water-borne cues derived from a predatory crayfish (Orconectes limosus (Rafinesque, 1817)) induced a doubling of the number of offspring released; these newly born snails were generally smaller, though more variable in size, and possessed a greater shell organic content than controls. The generally smaller size of juveniles released in the presence of a predator reflects a faster rate of generation and passage through the uterus. These responses to the presence of a predator could be adaptive by decreasing predation pressure within a population or by reducing mortality following failed attacks.