Final answer:
A fetus cannot experience a sense of smell primarily because their nostrils are plugged with skin cells and filled with amniotic fluid, coupled with an immature sensory system.
Step-by-step explanation:
The question 'what prevents the fetus from experiencing a sense of smell?' touches upon developmental biology and specifically fetal sensory development. During gestation, a fetus's nostrils are plugged with skin cells and subsequently filled with amniotic fluid. This physical barrier, in conjunction with the fact that the brain and olfactory system are not fully mature, plays a pivotal role in inhibiting the fetus's ability to detect odors. Although some cognitive development is essential for the interpretation of smells, the primary factors impeding a fetal sense of smell are the filled nostrils and the immaturity of the sensory systems. Newborn babies do exhibit a sense of smell soon after birth, as evidenced by their ability to recognize their mother's scent, which they have been exposed to via the amniotic fluid.