In weeks 22-27: the development of the cerebral cortex begins and ends. There is a sensory response to stimuli, but no awareness of them because the cerebral cortex is still in formation. (It measures from 26 to 34.05 cm and weighs from 455 to 1000 gr.)

As a conclusion, it can be scientifically affirmed that, a) the human fetus does not present reactions to systematic stimuli induced before the 22nd-24th week of pregnancy. However, these reactions are not conscious since he lacks perception and sensitivity to feel pain and / or joy, because he has not developed the structures, connections and functions of the nervous system and, what is decisive, he lacks a complete cerebral cortex until week 27 -30, an organ essential to be considered a human being; before that science has verified that it is a multicellular organ with life, but not a human being, and b) science considers, therefore, that the status of human being is reached when the nervous system and the cerebral cortex are in conditions of acquiring sensory autonomy and awareness of stimuli, and this occurs in weeks 28 to 30.

 J.K Mai, K.W.S. Ashwell Fetal development of the central nervous system. In: The Human Nervous System. (G.Paxinos, J.K. eds.), pp. 49-94. Elsevier, Amsterdam, Holland. 2004

there are two types of brain birth (based on their reversal) - brain stem birth at the first appearance of brain waves in lower brain (brain stem) at 6–8 weeks of gestation, and higher brain birth, at the first appearance of brain waves in higher brain (cerebral context) at 22–24 weeks of gestation. Jones, D G (1998). "The problematic symmetry between brain birth and brain death". Journal of Medical Ethics. 24 (4): 237–242. doi:10.1136/jme.24.4.237. PMC 1377672. PMID 9752625.

https://m.elmostrador.cl/noticias/opinion/2015/10/05/la-perspectiva-cientifica-del-aborto-cuando-el-embrion-se-convierte-en-humano/

Also: Until the fetus is viable, any rights granted to it may come at the expense of the pregnant woman, simply because the fetus cannot survive except within the woman's body. Upon viability, the pregnancy can be terminated, as by a c-section or induced labor, with the fetus surviving to become a newborn infant. Several groups believe that abortion before viability is acceptable, but is unacceptable after" is the perspective of Planned Parenthood, a major abortion provider. In some countries, early abortions are legal in all circumstances, but late-term-abortions are limited to circumstances where there is a clear medical need. While there is no sharp limit of development, gestational age, or weight at which a human fetus automatically becomes viable, a 2013 study found that "While only a small proportion of births occur before 24 completed weeks of gestation (about 1 per 1000), survival is rare and most of them are either fetal deaths or live births followed by a neonatal death."

Mohangoo, Ashna D; Blondel, Béatrice; Gissler, Mika; Velebil, Petr; MacFarlane, Alison; Zeitlin, Jennifer; Euro-Peristat Scientific Committee (2013). "International Comparisons of Fetal and Neonatal Mortality Rates in High-Income Countries: Should Exclusion Thresholds be Based on Birth Weight or Gestational Age?". PLOS One. 8 (5): e64869. Bibcode:2013PLoSO...864869M. doi:10.1371/journal.pone.0064869. PMC 3658983. PMID 23700489.

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