"The exact timing of the first nociceptive reflex responses to more traumatic mechanical stimulation is not known but they are unlikely to occur before the second trimester, somewhat later than responses to touch. It is known that the fetus withdraws from a needle from about 18 weeks and also launches a stress response following needle puncture. This stress response includes the release of hormones and neurotransmitters dependent on activity in areas of the midbrain. These findings confirm that signals about tissue damage are transmitted from the spinal cord and brainstem to the midbrain from at least 18 weeks."