What the Unborn
In addition to its rapid physical development in the
womb, which includes, as we have seen, an impressive
repertoire of movement patterns, the child's senses
also start to emerge during the prenatal period. As
noted previously, the olfactory nerve, which is integral
to the sense of smell, is present on the 35th day after
conception. The foundation of the sense of smell is
established on the 39th day when nerve fibers in the
brain connect with the olfactory lobe.
At eight weeks after conception, local stimuli can
induce partial closing of the fingers, opening of the
mouth, and squinting. And during the eleventh week,
if the region around the mouth is stimulated, the child
will open its mouth and suck a finger.
The child can respond to sounds from the tenth to fourteenth
weeks after conception. Changes in its heart rate, eye
blinks and movements have occurred after sounds.
Taste buds begin to form during the eighth week after
conception. An unborn child actually has more taste
buds than a newborn and probably has a sense of taste.
The reflexes between the taste buds and facial muscles
are in place by the twenty sixth to twenty eighth weeks
after conception. A facial response was evoked at this
time when a bitter-tasting substance was given to a
Unborn children may have a sweet tooth. In one case,
a child swallowed more amniotic fluid when it was sweetened.
In another, the child responded to the addition of a
bad-tasting substance to the amniotic fluid by reducing
its sucking movements.
We can't, of course, ask an unborn child if it experiences
pain. However, research suggests that the answer would
likely be that it does.
From the fifth week after conception onward, pain pathways
are running from sensory receptors in the skin to those
in the brain. These nerve endings are at least as dense
in the skin of a newborn as in an adult. Such receptors
appear around the mouth during the fifth week after
conception and are present in the face, palms, and soles
of the feet by the ninth week, spreading to the trunk,
arms and legs by the thirteenth weeks and to all areas
of the skin by the eighteenth week.
The development of the neocortex, the largest part
of the brain, begins six weeks after conception and
a full complement of nerve cells is present by the eighteenth
week. At this time the pieces are in place to complete
the pain circuitry. The evidence thus indicates that
the child has developed sufficiently to sense pain late
In a study of women undergoing amniocentesis during
the third trimester, the sudden burst of body movements
that the child made during the procedure may reflect
a response to pain. These movements occurred when the
needle either struck the child or the child moved against
the needle. In another study, the child's heart rate
increased in response to scalp blood sampling, a procedure
that is likely to be painful.