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Fetal Development
Prenatal development
• The period from conception moving through
the 3 stages (Zygote, Embryo, Fetus)
• Physical changes that take place before the
baby is born.
Fetal Development Terms
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Ovum: A female cell or egg – for reproduction
Uterus: A female organ where baby develops
Sperm: A male cell for reproduction
Conception: A union of ovum and sperm
resulting in the beginning of pregnancy.
• Zygote: A fertilized egg.
Stage
Time Span
Stages, Time Span and
Development
That Occurs
Development
Zygote travels down
the Fillopian tube and
attaches to the lining
of the uterus.
Zygote
Conception – 2
weeks
Embryo
Wk. 3-8
Rapid growth and
change. Mass of cells
develop into all major
body systems. Sac of
amniotic fluid forms
around embryo.
Placenta Forms.
Fetus
Wk. 8-9 (begins)
Until birth
Wk. 4-5 kicks
Growth lg.
Wk. 28 can live
outside womb.
36 wks lungs
developed.
Important Terms
• Placenta: A tissue in the uterus of a pregnant woman
that is rich in blood vessels and plays a role in bringing
food and oxygen from the mother’s body to a
developing fetus.
Amniotic Fluid: Liquid that surrounds and protects the
developing baby in the uterus during pregnancy.
Umbilical cord: A long tube that connects the placenta to
the developing baby; carries food and oxygen to the
baby.
More Terms
• Quickening: Signs (kicking , fluttering etc. ) telling
a pregnant woman that she has a live baby
developing in her body. (4-5 wks)
• Lightening: The baby shifting down. The pregnant
woman feels lighter in the upper abdomen and
heavier in the lower abdomen. The baby is
dropping into the birth canal in preparation for
delivery. (usually in the 9th month)
Heredity
• The passing on of certain characteristics from
earlier generations.
• Characteristic that can be hereditary:
• Physical build; skin color; hair texture and
color; colour and shape of eyes; shape and
size of the ears, hands and feet; and blood
type.
Chromosomes and Genes
Chromosomes consist of many genes
• At conception every human baby receives 46
chromosomes. These chromosomes come in 23
pairs. The father’s sperm and the mother’s ovum
both contribute a chromosome to each pair. Each
chromosome has thousands of genes, the units
that determine the child’s inherited
characteristics. Genes make up chromosomes as
like beads make up a necklace.
Dominant and Recessive Genes
• What happens if a baby has a mother with
blue eyes and a father with brown eyes?
- The way the characteristic (brown or blue eyes)
is expressed will be controlled by the
DOMINANT or stronger gene. The RECESSIVE
or weaker gene will be lost.
• In this example BROWN EYES ARE DOMINANT
so what colour eyes will the baby most likely
have?
Answer
• The baby would most likely have brown eyes
because BROWN is DOMINANT however there
would be a slight chance he/she would have
BLUE eyes IF both parents had RECESSIVE blue
eye genes.
More precisely if the person with the brown
dominant also had a blue recessive then the
baby could have blue eyes.
What determines the sex of a baby?
• At conception, gender is determined by
chromosome characteristics - and it is the male's
sperm that dictates whether the baby will be a
boy or a girl. Prior to conception, the unfertilized
egg carries an X chromosome while the sperm
can carry either an X or a Y chromosome. The
gender of the baby comes down to one simple
event:
• If the sperm carrying an X chromosome fertilizes
the egg, a girl will be conceived.
• If the sperm carrying a Y chromosome fertilizes
the egg, a boy will be conceived.
Multiple Births
• Fraternal Twins: 2 eggs fertilized resulting in non indentical twins
(siblings but different genetics) - could be same sex or opposite sex
.Fraternal twins are hereditary. They do not always “skip a
generation”.
• Identical Twins: 1 eggs is fertilized and splits. No one really knows
why the egg splits. It is considered a “fluke of nature”. Identical
twins have the same genetic make up since they come from the
same fertilized egg. The later the egg splits, the more dis-similar the
twins will be. Identical twins are always same sex twins due to the
identical genetics. Identical twins are not hereditary.
• Both Fraternal and Identical Twin pregnancies are considered high
risk pregnancies however identical twin pregnancies are slightly
greater risk due to the fact that most of the time identical twins
share a placenta and sometime this can cause problem. Eg. Twin to
Twin Transfusion Syndrome.
Triplets
• More common as twins are now due to fertility
treatments such as in-vitro fertilization whereby
three or more embryos are implanted.
• Usually fraternal triplets. In rare cases you may
have triplets as a result of two eggs being
fertilized and the one of the eggs splits to create
and identical set.
• Higher order multiples are very rare unless
fertility treatments are involved and pose ethical
questions that can not be ignored. Eg. selective
reduction.
Infertility
• Infertility is the inability to become pregnant
• It is estimated that one in six couples has trouble
conceiving.
• Some reasons for females infertility are:
• - Ovulation problems: her ovaries are not
releasing eggs each month
• - endometriosis (the endometrial tissue or
uterine lining grows outside of the uterus)
• Other causes: polycystic ovary syndrome, poor
egg quality, fallopian tube blockages.
Infertility options
• Adoption: A couple is given the legal rights to a child already born.
• Artificial Insemination: Sperm is injected into a woman.
• In vitro fertilization: A egg from the woman is removed and
fertilized with sperm from the man. The resulting zygote is placed in
the woman’s uterus.
• Ovum transfer: A female donor is used for in-vitro. In this case a
woman may not have working ovaries or may have an inherited
disease so they use a donor.
• Surrogate mother: A woman gets pregnant for a couple. The
couple’s fertilized eggs can be used or artificial insemination can be
done.
• NB: Fertility drugs can be used to stimulate ovulation or treat
infertility. These medications can cause serious side effects such as
lung probbems, abdominal pain etc. Another side effect can be
multiple births.
Infertility
• Male Infertility
• - Some causes for male infertility are:
- Male tube blockages
- Sperm problems (low sperm count or a
motilty problem)
- Sperm allergy – woman develops antibodies
that kills sperm.(diagnosis is controversial)