Simple SummaryA key event in the life of a mammalian fetus is its birth, especially in view of the exceptional change in its environment that occurs at birth. An area of great interest is the extent to which factors within the uterus prepare the fetus for birth and postnatal life. These and other factors are evaluated here for mammalian young that exhibit mature, moderately immature, and exceptionally immature neurological development at birth. A striking finding is the basic uniformity of various preparatory processes despite the diversity of birth-related circumstances among different terrestrial mammals. Numerous scientific disciplines have contributed to understanding in this area. Accordingly, the major purpose of this review is to construct from these diverse sources an integrated account of important facets of our current understanding. The primary focus is on how a progressive improvement in the functional effectiveness of the sensory systems for touch, temperature, taste, smell, balance/movement, hearing, and sight equips young mammals to cope successfully with the considerable challenge of being expelled from the uterus into the outside world. It is shown that the sensory environment in the uterus interacts with the genetically preprogrammed development of the apparatus for each sensory modality. It is also shown that the way this occurs can embed stimulus-response capabilities that can be accessed and beneficially utilised after birth. This phenomenon is called “trans-natal sensory continuity”. This embedding of sensory capabilities has previously been described as “learning” and the subsequent accessing of these embedded capabilities as “memory”. However, it is noted that such “learning” and “memory” processes are sometimes mistakenly thought to require the fetus to be conscious, a view which does not accord with established understanding of learning processes, nor with compelling contrary evidence from direct studies of fetal brain states. The solution proposed is to describe trans-natal sensory continuity in terms of the neurophysiological mechanisms involved and not as learning and memory outcomes. Introduced here, therefore, is the concept of “intrauterine sensory entrainment”. Its specific mechanistic basis is the well-established way nervous systems respond to sensory stimuli by reorganising their neural structures, functions, and connections. Known as neuroplasticity, this is recognised as integral to both prenatal and postnatal brain development and as the basis of postnatal learning and memory. Thus, intrauterine sensory entrainment is the mechanism by which trans-natal sensory continuity is achieved. It begins with the prenatal embedding of responsiveness to particular sensory inputs which are generated by the stimulation of specific receptors once the neurological apparatus for that sensory modality has begun to develop. Thereafter, this process continues until birth, and this makes all such entrained sensory capabilities available to operate after birth. Nevertheless, all sensory systems th...
