Fetal Awareness - Review of Research and Recommendations for Practice | Royal College of Obstetricians and Gynaecologists

http://www.rcog.org.uk/fetal-awareness-review-research-and-recommendations-practice

In reviewing the neuroanatomical and physiological evidence in the
fetus, it was apparent that connections from the periphery to the
cortex are not intact before 24 weeks of gestation and, as most
neuroscientists believe that the cortex is necessary for pain
perception, it can be concluded that the fetus cannot experience pain
in any sense prior to this gestation. After 24 weeks there is
continuing development and elaboration of intracortical networks such
that noxious stimuli in newborn preterm infants produce cortical
responses. Such connections to the cortex are necessary for pain
experience but not sufficient, as experience of external stimuli
requires consciousness. Furthermore, there is increasing evidence that
the fetus never experiences a state of true wakefulness in utero and
is kept, by the presence of its chemical environment, in a continuous
sleep-like unconsciousness or sedation. This state can suppress higher
cortical activation in the presence of intrusive external stimuli.
This observation highlights the important differences between fetal
and neonatal life and the difficulties of extrapolating from
observations made in newborn preterm infants to the fetus.

---SPSmith