D-instantons of type IIB string theory are Ramond-Ramond counterparts of Giddings-Strominger wormholes connecting two asymptotic regions of spacetime. Such wormholes, according to Coleman, might lead to spacetime topology change, third-quantized baby universes and probabilistic determination of fundamental coupling parameters. Utilizing holographic correspondence between AdS₅ × M₅ type IIB supergravity and d = 4 super-Yang-Mills theory, we point out that topology change and sum over topologies not only take place in string theory but also are required for consistency with holography. Nevertheless, we argue that the effects of D-instanton wormholes remain completely deterministic, in sharp contrast to Coleman's proposal.