Prenatal Development

1
Prenatal Development
2
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).

3
Review The 3 stages of prenatal development

• 1) Germinal Stage (Period of the zygote)
• First 2 weeks of pregnancy
• 2) Embryonic Stage (Period of the Embryo)
• 3rd to 8th week of pregnancy
• 3) Fetal Stage (Period of the fetus)
• 9th week to end of pregnancy/birth
• They occur in the above order

4
Conception

• Each month a womans 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 womans
  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.

5
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.

6
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 mothers
  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.

7
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.

8
Period of the fetus Contd

• Between the fourth and fifth month of pregnancy
  the fetuss 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 babys
  fetal age and its birth date.

9
Period of the Fetus Contd 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 babys 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).

10
Ready for Birth

• The baby is now turned head down in the lower
  pelvis and is ready to be born.

11
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 full-term 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
  babys legs are straight and held flat against
  his/her body. There is the rare footling breech
  where the babys foot or feet are coming first
  (before their bottom). There is the very rare
  kneeling breech where the baby is in a kneeling
  position.