Part 2: Stages of human development,
three week old embryo to a newborn:
The following information is approximate & intended for general information.
Every pregnancy is different. Development varies from fetus to fetus.
Do not rely on this information for personal medical decisions.
The process leading up to the birth of a newborn baby can be divided into many steps (Continued):
3 weeks: The embryo is now about 1/12" long, the size of a
pencil point. It most closely resembles a worm - long and thin and with
a segmented end. Its heart begins to beat about 18 to 21 days after
conception. Before this time, the woman might have noticed that
her menstrual period is late; she might suspect that she is pregnant and conduct a pregnancy test. In the U.S., about half of all pregnancies are unplanned. About half of these are terminated by an abortion.
4 weeks: The embryo is now about 1/5" long. It looks something like a
tadpole. The structure that will develop into a head is visible, as is a noticeable tail.
The embryo has structures like the gills of a fish in the area that will later develop
into a throat.
5 weeks: Tiny arm and leg buds have formed. Hands with webs between the fingers
have formed at the end of the arm buds. Fingerprints are detectable. The face "has
a distinctly reptilian aspect....the
embryo still has a tail and cannot be distinguished from pig, rabbit,
elephant, or chick embryo [at this stage of development]" 1
6 weeks: The embryo is about 1/2" long. The face has two eyes, one on
each side of
its head. The front of the face has "connected slits where the mouth and nose
eventually will be."2
7 weeks: The embryo has almost lost its tail. "The face is mammalian but
somewhat pig-like."1 Pain sensors appear.
Many religious and social conservatives believe that the embryo at this stage can feel pain.
However, the higher functions of the brain have yet to develop, and the
pathways to transfer pain signals from the pain sensors to the brain
do not exist at this stage of development.
2 months: The embryo's face resembles that of a primate but is not fully human in
appearance. Some of the brain begins to form; this is the primitive "reptilian brain" that
will function throughout life. The embryo will respond to prodding, although it has no
consciousness at this stage of development. The brain's higher functions are not active until much later in pregnancy when the fetus becomes sentient.
10 weeks: The embryo is now called a fetus. Its face looks human. Its genetic gender may
be predicted from the presence or absence of a penis during an ultrasound test.
13 weeks or 3 months: The fetus is about 3 inches long and weighs about an ounce.
bones can be seen. Over 90% of all abortions are performed before this stage, before the fetus has become conscious, and therefore before it is sentient. 3
17 weeks or 3.9 months: It is 8" long and weighs about a half pound. The fetus' movements may
begin to be
felt. Its heartbeat can usually be detected by a physician with a stethoscope.
20 weeks or 4.6 months: Many social and religious conservatives with pro-life views assert that a fetus can feel pain at 20 weeks. They have successfully passed legislation in some states to prohibit abortions after this time. Other activists call for anesthetic to be administered during abortions of fetuses 20 weeks or later to prevent them from feeling pain.
House bill H.R. 36 was been filed in Congress to prohibit abortions after this point in gestation unless the woman is the victim of rape or incest or if a continued pregnancy would endanger her life. It does not contain an exception for cases in which a severe fetal abnormality is detected after 20 weeks. It is based on the belief of its sponsors that a fetus can feel pain at this time -- a belief which very few medical researchers agree. The bill has been passed by the Republican dominated House. However, the bill was stalled in the Senate as of mid 2015-OCT. 4
22 weeks or5 months: 12" long and weighing about a pound, the
fetus has hair on its head. Its movements can probably be felt by the mother. An elective abortion is usually
unavailable at this gestational age because of state and province medical
society regulations, except under very unusual circumstances. The vast majority of fetuses who are born at 22 weeks died or suffered serious health issues. 7 However, half-way through
the 22nd week, the fetus' lungs may be developed to the point where it
would have a
miniscule chance to live on its own. State laws and medical association regulations
generally outlaw almost all abortions beyond 20 or 21 weeks gestation.
baby born during the 22nd week has a 14.8 percent chance of survival.
And about half of these survivors are brain-damaged, either by lack of oxygen
(from poor initial respiration) or too much oxygen (from the ventilator).
Neonatologists predict that no baby will ever be viable before the 22nd week, because before then, the lungs are not fully formed." 5
Of course, if someone develops an artificial womb to which a fetus could be transferred, then this limit could change
Fetal survival rate:
"Most babies at 22 weeks are not
resuscitated because survival without major disability is so rare. A baby's
chances for survival increases 3 to 4% per day between 23
and 24 weeks of gestation and about 2 to 3% per day between 24 and 26 weeks of gestation. After 26 weeks the rate of survival
increases at a much slower rate because survival is high already." 6
26 weeks or 6 months: The fetus 14" long and almost two pounds. The lungs' bronchioles develop. Interlinking of the brain's neurons begins. The higher
functions of the fetal brain turn on for the first time. Some rudimentary brain waves indicating consciousness can be detected. The fetus will probably be able to feel pain for the first time. It has become conscious to some degree of its surroundings. The fetus has become a sentient human life for the first time. Some pro-choicers define this point as the point where human personhood is attained. Some reason that a fetus without functioning higher brain functions more closely resembles a doll, than a newborn.
7 months or 30.5 weeks: 16" long and weighing about three pounds. Regular brain waves are detectable which are similar to those in adults.
8 months or 35 weeks: 18" long and weighing about 5 pounds.
9 months or 39 weeks: 20" long and with an average weight of about 7 pounds,
a full-term fetus' is typically born about this time.
The Visible Embryo is a remarkable web site. It shows the various stages of development from a fertilized egg to fully-formed fetus.
"The inside story" at StandUpGirl also shows fetal images, taken by 3-D ultrasound, 4-D ultrasound, and contact embryoscopy.
See: http://www.standupgirl.com/ Caution: the web site shows some drawings and pictures of a fetus early in pregnancy, and add an unrelated comment that describes a viable fetus near the end of pregnancy.
Religious and social conservatives generally believe that pregnancy begins
at conception, whether achieved through sexual
intercourse or in-vitro fertilization (IVF). In the latter case, conception is
performed in a dish external to the woman's body. Typically, two dozen of the
woman's ova are harvested, and fertilized in the lab. The three or four most
vigorous pre-embryos are then selected and implanted in her uterus. The rest are
discarded, exposed to die, or frozen for possible future use. Sometimes, only a single pre-embryo is implanted. This is done in order to reduce the chances of a multiple birth.
The following information sources were used to prepare and update the above essay. The hyperlinks are not necessarily still active today.
Drs. R.D. Tribhuwan & B.D. Patil, "Body image, human reproduction and birth control," Discovery Publishing House, 2009, at: https://books.google.ca/
Carl Sagan, "Billions and Billions", Random House, New York NY (1997), Pages 163-179.
This ultrasound picture of a fetus at 2.8 month/12 week gestation was donated by a visitor to this web site.