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tazzygirl -> RE: Foetus and pain. (6/26/2010 5:56:51 AM)
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In the US, a preterm labor will be allowed to take its course if the pregnancy is not beyond the 20 week period. The fetus is just not viable up to that point.
Now, for some science.
quote:
Fetal stages of development:
In 3 percent of all pregnancies, there will be a serious structural abnormality of the fetus, the most common being central nervous system and cardiovascular defects. The most detailed survey of fetal anatomy is carried out at the mid pregnancy scan at 20-22weeks , but a screen of fetal anatomy will be carried out at any stage if there are risk factors for congenital abnormalities. The overall detection rate for abnormalities is 70 -80 percent. False positive rates are exceptionally low and research shows that parents elect t terminate the pregnancy in 80 to 90 percent of the cases.
There is even a nice fetal development chart on this source.
http://www.news.kenzoo.info/health/fetus-growth.htm
quote:
The first half of the fetus' gestation (the first 20 weeks) is characterized by neuroblast proliferation while the second half of gestation is characterized by "brain growth spurt." During this latter time, structural growth is marked by glial cell formation (interstitial or supportive tissue of the nervous system), nerve fiber myelination, and arborization (branching) of the dendrites.
1. Neuronal Proliferation
A neuron consists of 3 parts: the dendrite that brings the message to the cell; the soma or cell body that receives and transmits the message; and the axon that transfers the message to the next neuron. Neuronal proliferation occurs initially at 2 months gestation, peaking at about 26 weeks'. Nearly all neurons are present by 18-20 weeks' gestation but their function is primitive because of the lack of myelination and arborization of the dendrites. Prenatal exposure to toxins or inherited diseases at this time can significantly alter the final number of neurons. On the other hand, prenatal exposure to chemical and environmental substances can reduce the final number of neurons. Glial cell proliferation, the supporting tissue of the CNS, occurs at about 5 months gestation.
The dendrites form the interneuronal synaptic connections or electric circuitry of the brain. Initially, dendrites appear as thickened processes with only a few spines or branches extending out from them. However, as the gestation progresses these spines or branches increase in number and length and become the site for synaptic connections, ultimately linking one neuron with up to 1000 other neurons. The critical growth time for this branching is the last trimester of a pregnancy and is very dependent on the fetus' ability to maintain metabolic homeostasis (adequate blood oxygen, normal pH) and adequate nutrition (vitamins, glucose, fatty acids, amino acids). An insufficient intake by the mother and fetus of glycoproteins and glycolipids may hinder dendrite arborization and/or synaptic connections.
2. Neuronal Migration
Neuronal migration refers to the movement of nerve cells from their sites of origin in the ventricular and subventricular zones to their final destination in the CNS. While migration can occur as early as 2 months' gestation, the peak time for migration is 3-5 months' gestation. However by the 6th month of gestation, neuronal migration to its permanent place in the cerebral cortex has been completed. Neuronal migration is important for the appropriate development of the cerebral cortex, basal ganglia, hypothalamus, thalamus, brainstem, cerebellum, and spinal cord. Failure to complete normal neuronal migration may result in abnormalities in cortical development and neurologic functioning. It may also precipitate other abnormal neurologic development that we may see manifested in the neonatal period as seizures.
3. Neuronal Organization
Neuronal organization is the basis for brain function. It involves the alignment and layering of the cerebral cortex; arborization of axons and dendrites; establishment of synaptic connections; cell differentiation and death; and finally, proliferation and differentiation of the glial cells. Glial cell proliferation and differentiation is extremely important as it provides the supporting tissue for the CNS. Although the glial cells resemble the neuron structurally, they are not able to transmit nerve impulses.
http://www.capefearvalley.com/outreach/outreach/modules/cnsivh/pages/Embryology.htm
I know alot of this is technical, but i post it with good reason. It is shown that around 20 - 25 weeks gestation the CNS is almost completely in full swing. I dont believe anyone is arguing that fact. But, since many insist on facts, i have one more to post.
quote:
By gestational age and method
In 2003, from data collected in those areas of the United States that sufficiently reported gestational age, it was found that
88.2% of abortions were conducted at or prior to 12 weeks,
10.4% from 13 to 20 weeks,
and 1.4% at or after 21 weeks
Similarly, in England and Wales in 2006,
89% of terminations occurred at or under 12 weeks,
9% between 13 to 19 weeks, and
1.5% at or over 20 weeks.
http://en.wikipedia.org/wiki/Abortion
Out of those performed at over 20 weeks gestation, most are done for the health of the mother or because of severe medical complications within the fetus. Recall the previous exerpts i offered stating that many tests performed on a fetus are done so at the 20-22 week stage, revealing any problems with the CNS among other systems.
Do fetuses at 24 weeks feel? Im sure they do. and some can survive. But, at the 20 week period and beyond, its now a matter of quality of life, viability out of utero, and potential complications later. The majority of abortions are not medically induced, by happen naturally. The medically induced ones typically occur before 10-12 weeks.
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