The Fetus
Chapter 3
1. At what point in a baby’s development is the sex, color of
hair and eyes as well as other physical characteristics
determined?
At conception
2. How is the sex of the baby
determined?
The egg carries two X chromosomes and
the sperm carries both an X chromosome
and a Y chromosome.
If the egg is fertilized with an X chromosome
it is a female; if it is fertilized with a Y
chromosome it is a male
3. List four factors that affect the
chances of having twins:
• A. Age – twins are less common in
younger mothers
• B. Number of children – Twins are less
common in first pregnancies
• C. Race – People of African descent are
more likely to have twins
• D. Family History – do twins run in your
family?
4. What is the difference between
fraternal and identical twins?
• Fraternal Twins occur when 2 eggs are
fertilized with two sperm. There are two
separate embryos. It is possible to have
different sex fraternal twins.
• Identical Twins occur when 1 egg is
fertilized by one sperm and then divides
into two separate embryos. Identical twins
are always the same sex.
5. Why is the unborn baby not likely to
feel anything if the mother falls during
pregnancy?
• The baby is buoyant and is protected by
the amniotic fluid in the amniotic sac.
6. What is “quickening”?
The mother feels fluttering movements –
they are faint at first and may be mistaken
for “gas”. Eventually they become
stronger and more frequent as the baby
grows. The baby has been active long
before the mother first feels this movement
When does the mother first feel this
movement?
18 – 20 weeks
7. Why does it not bother a baby to be
upside down in her mother’s uterus?
The baby is weightless and does not feel the
pull of gravity. This is very similar to
astronauts in space.
a. What is the fetal position?
It is when the fetus curls up in the womb
because there is no longer enough room
to stretch out.
8. Why does the skull remain flexible
and the final fusion of the skull bones
happen just before puberty?
The Baby must get through the birth canal
at birth
and the brain is not fully developed and
does not stop growing until puberty.
Fetal Developmental Chart
First Month:
In the first 2 weeks:
• The fertilized egg is called a zygote.
• During this time the zygote reaches the uterus and
attaches to the lining of the uterus.
• Attachment of the zygote signals the uterus that nutrition
from the lining of the uterus is needed and it is not shed
and the woman misses her first period and does not
usually resume having a period until after the birth of the
child.
• Although the zygote is experiencing tremendous growth
at this time, it is only the size of a pinhead
In the next 2 weeks:
•Internal organs and the circulatory
system begin to form
•The heart begins to beat
•By the end of the month small
bumps indicate the beginning of
arms and legs
•The eyes, brain, and spinal cord
are beginning to form
•The fetus is the size of a pea
Second Month (8 weeks)
•
•
•
•
•
At 5 weeks the embryo is about ¼” long
Face, eyes, ears, and limbs take shape
Bones begin to form
Internal organs begin to form
Brain is developing rapidly
Third Month (12 weeks)
• As the month begins the fetus is about 1” long
• Nostrils, mouth, lips, tooth buds, and eyelids
form
• Fingers and toes are almost complete
• Has finger- and toe- nails
• All organs are present but immature
• Fetus begins to move a little
• Hair may begin to appear
Fourth Month (16 weeks)
• The fetus is about 3” long and weighs about 1
ounce
• The fetus can suck its thumb, swallow, hiccup
and move around
• Facial features become clearer
• Secondary sexual characteristics are formed
• There is a tiny chin
• Eyes seem too far apart
• At the end of this month the development period
is over and the growth phase begins
Fifth Month (20 weeks)
• The fetus is about 6.5 – 7” long and 4 – 5
ounces in weight
• Hair, eyelashes, and eyebrows appear
• Teeth continue to develop (inside the
gums)
• Organs continue to mature
• The fetus becomes more active
Sixth Month (24 weeks)
• The fetus is now 8 – 10 inches long and
weighs between 8 and 12 ounces
• Fat is being deposited under the skin, but
the fetus still appears wrinkled
• Breathing movements begin
• Taste buds appear
• Lungs are immature
Seventh Month (28 weeks)
• The fetus is 10 – 12 inches long and 1.5 to 2
pounds
• Periods of fetal activity are followed by period of
rest and quiet
• The fetus is covered by vernix – a cheese-like
secretion to prevent the skin from becoming
water-logged
• Organs are still immature
• Umbilical cord has reached its maximum length
Eighth Month (32 weeks)
• Weight gain continues rapidly
• The fetus is 14 – 16 inches long and 2.5 – 3
pounds
• The fetus may react to loud noises with a
reflexive jerking action
• In most cases the fetus moves into a head down
position
• The fetus becomes less active as they grow and
have less room to move
• Lungs are developing
Ninth Month (36 weeks)
• At the beginning of the 9th month the fetus is
about 17 – 18 inches long and weighs about 5 –
6 pounds
• Skin becomes smooth as fat deposits continue
to build
• Fetal movements decrease as the fetus has less
room to move around
• The fetus acquires disease-fighting antibodies
from the mother’s blood
• The fetus descents into the pelvis, ready for birth