A fetus can potentially feel pain as early as 12 weeks of gestation according to some neuroscientific evidence, although the dominant medical opinion typically places fetal pain perception at 24 to 25 weeks gestation or later.

Early Possibility of Fetal Pain (as early as 12 weeks)

• Neural pathways for pain perception via the cortical subplate are present as early as 12 weeks, and via the thalamus as early as 7-8 weeks.
• The cortex may not be necessary for the experience of pain; consciousness and pain perception may be mediated by subcortical structures like the thalamus and brainstem, which develop in the first trimester.
• Fetal pain-related neurotransmitters such as substance P and enkephalins appear as early as 7 weeks.
• Some evidence from fetal surgery practices suggests fetal analgesia is given starting in the second trimester (after 14 weeks) to manage pain responses.

Medical Consensus on Later Pain Perception (around 24-25 weeks)

• Major medical organizations such as the American College of Obstetricians and Gynecologists (ACOG) typically hold that a fetus cannot feel pain until the cortex and thalamus connections mature around 24 weeks.
• Responses to noxious stimuli before this time are likely reflexive or hormonal reactions, not conscious pain perception.
• By 24-25 weeks, fetuses show physiological reactions such as increased heart rate and blood pressure to painful stimuli.
• Premature infants born as early as 21-22 weeks demonstrate pain responses, supporting the view that early preterm babies can feel pain.

In summary, while there is ongoing debate, the possibility of fetal pain perception exists as early as 12 weeks based on neurological development, but clinical and policy consensus largely places pain perception at around 24-25 weeks gestation.