Electroencephalography indicates that the capacity for functional pain perception in premature infants does not exist before 29 or 30 weeks; a 2005 meta-analysis states that withdrawal reflexes and changes in heart rates and hormone levels in response to invasive procedures are reflexes that do not indicate fetal pain.<ref name="Lee"/>
Several lines of evidence suggest that a fetus does not awaken during its time in the womb. Much of the literature on fetal pain simply extrapolates from findings and research on premature babies. The presence of such chemicals as [[adenosine]], [[pregnanolone]], and [[prostaglandin]]-D<sub>2</sub> in both human and animal fetuses, indicate that the fetus is both [[sedation|sedated]] and [[anesthesia|anesthetized]] when in the womb. These chemicals are oxidized with the newborn's first few breaths and washed out of the tissues, increasing consciousness.<ref>{{Cite journal|last1=Lagercrantz|first1=Hugo|last2=Changeux|first2=Jean-Pierre|date=March 2009|title=The Emergence of Human Consciousness: From Fetal to Neonatal Life|url=http://www.nature.com/doifinder/10.1203/PDR.0b013e3181973b0d|journal=Pediatric Research|volume=65|issue=3|pages=255–260|doi=10.1203/PDR.0b013e3181973b0d|pmid=19092726|s2cid=39391626|issn=0031-3998|quote=The delivery from the mother's womb thus causes arousal from a "resting," sleeping, state in utero. After birth, electrophysiological signs on EEG scalp recordings indicate an intense flow of novel sensory stimuli after birth… In addition, arousal is enhanced by the release from endogenous analgesia possibly caused by removal of the mentioned placental "suppressors" which in utero selectively inhibit neural activity of the fetus…. The catecholamine surge triggered by vaginal delivery may also be critical for the arousal at birth.|doi-access=free}}</ref> If the fetus is asleep throughout gestation then the possibility of fetal pain is greatly minimized,<ref name="Diesch">{{cite journal |doi=10.1016/j.brainresrev.2005.01.006 |pmid=16269314 |title=The importance of 'awareness' for understanding fetal pain |journal=Brain Research Reviews |volume=49 |issue=3 |pages=455–71 |year=2005 |last1=Mellor |first1=David J. |last2=Diesch |first2=Tamara J. |last3=Gunn |first3=Alistair J. |last4=Bennet |first4=Laura |s2cid=9833426 }}</ref><ref>{{cite news|last=Paul|first=AM|title=The First Ache|url=https://www.nytimes.com/2008/02/10/magazine/10Fetal-t.html|newspaper=The New York Times|date=2008-02-10}}</ref> although some studies found that the adenosine levels in third-trimester fetuses are only slightly higher than those in adults' blood.<ref>{{cite journal |doi=10.3109/14767058.2011.632040 |title=Is fetal pain a real evidence? |journal=[[The Journal of Maternal-Fetal & Neonatal Medicine]] |volume=25 |issue=8 |pages=1203–8 |year=2012 |last1=Bellieni |first1=Carlo Valerio |last2=Buonocore |first2=Giuseppe |pmid=22023261 |s2cid=20578842 }}</ref>
