Prenatal Development
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Notes:
 Prenatal
refers to the period of time
before birth. It is during this 40 week
period (about nine months) that one cell
develops into a human infant. The
prenatal development begins immediately
as the mother conceives (the sperm meets
the egg).
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Review: The 3 stages of prenatal
development

1) Germinal Stage: (Period of the zygote)


2) Embryonic Stage: (Period of the Embryo)


3rd to 8th week of pregnancy
3) Fetal Stage: (Period of the fetus)


First 2 weeks of pregnancy
9th week to end of pregnancy/birth
*They occur in the above order
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Conception

Each month a woman’s ovary
releases a cell or egg called the
ovum. The egg moves from the
ovary into the Fallopian tube and
into the uterus. This travel takes
about two to three days.

If the egg reaches the uterus
before it meets a sperm it is
flushed away with the woman’s
menstrual flow. However, if the
egg is fertilized before it reaches
the uterus then it will implant itself
in the uterine wall. The egg can
only be fertilized in the Fallopian
tube. If the egg does become
fertilized in the Fallopian tube then
it is at this point that a woman had
conceived.
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Period of the Zygote

The period of the
ovum/germinal/zygote stage is the first
stage in the life of a human baby. This
stage lasts for approximately two
weeks immediately after conception.

When the fertilized egg reaches the
uterus, it attaches itself to the uterine
wall; the thickened lining of the uterus
that is shed through menstruation if
the woman has NOT conceived, and
begins to grow. The lining in the
uterus is used to nourish the fertilized
egg. The egg grows by a process
called cell division. The single cell
divides and becomes two, two become
four, four become eight and so on until
there are millions of cells. Each cell is
preprogrammed to become the skin,
the bones, the hair, etc of the baby. At
the end of this two week period the
ovum is still only the size of a pinhead.
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Period of the Embryo

The second stage of life is the period
of the embryo and it lasts for about six
(6) weeks. The embryo becomes
firmly attached to the inner lining of the
uterus. By the end of this stage the
connecting tissue between the embryo
and the lining becomes the placenta.
The placenta provides nourishment
and oxygen from the mother’s blood
stream to the embryo through the
umbilical cord.

The growing embryo is soon
surrounded by a bag of liquid called
amniotic fluid which acts like a
cushion to protect it through minor
bumps or falls of the mother. The
baby remains in this sac of liquid until
just before birth. It is the amniotic sac
that breaks when women refer to their
“water breaking.”
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Period of the Fetus

The period of the fetus is the
third and last stage of
development of the baby,
during pregnancy. The embryo
becomes a fetus around the
8th-9th week of pregnancy until
the end of the pregnancy. It is
during this period that the
unborn baby becomes more
recognizable; with legs, arms,
sex organs, even fingers and
toes. While all the internal
organs are present at the
beginning of this period, they
are not all yet functioning.
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Period of the fetus Cont’d

Between the fourth and fifth
month of pregnancy the fetus’s
movements touch the wall of
the uterus. The feeling the
mother gets with these initial
movements is sometimes
called “quickening” as it is now
apparent to the mother that
she has life inside of her.
However, the baby has
actually been active long
before this. By knowing when
the expecting mother first felt
life the doctor can better
determine the baby’s fetal age
and its birth date.
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Period of the Fetus Cont’d 2

The unborn baby can suck its
thumb, cough, sneeze, yawn
and suffer hiccups. It can also
cry, although you can not hear
it. During the ninth month of
prengnancy the baby’s weight
will shift suddenly. This allows
the mother to feel more
comfortable. This movement
is called “lightening.” This
means that the baby has
dropped into the lower pelvis
and is ready for delivery (head
down).
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Ready for Birth

The baby is now
turned head down in
the lower pelvis and is
ready to be born.
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Breech babies

Breech babies present with their bottoms
down and their heads up. When a woman
is 28 weeks pregnant, her baby has a
25% chance of being in the breech
position. As the pregnancy progresses,
the likelihood of a baby staying in the
breech position gets smaller. At 33 weeks
of pregnancy there is around a 5%
chance of a breech presentation. At fullterm around 3-4% of babies remain in the
breech position. There are different types
of breech babies and they are described
by the position that they are in. There is
the ‘complete breech’ which is where the
baby sits cross legged. The “frank
breech” where the baby’s legs are
straight and held flat against his/her
body. There is the rare ‘footling breech’
where the baby’s foot or feet are coming
first (before their bottom). There is the
very rare ‘kneeling breech’ where the
baby is in a kneeling position.
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