Pain and stress in the human fetus.

Invasive diagnostic and therapeutic techniques are increasingly applied to the fetus. It is not known if the fetus feels pain during such procedures, but the fetus does mount significant stress hormonal and circulatory changes in response to these from 18-20 weeks. Perinatal stress may have long-term neurodevelopmental implications. During open fetal surgery, maternal general anaesthesia provides fetal anaesthesia. However, in closed procedures, fetal analgesia presents difficulties. The optimal drug, dose, and route of administration remain to be determined.