Transcript Conception & Fetal Development

Conception & Fetal
Development
By
Dr. Aida Abd El-Razek
Learning Objectives
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Define the key terms.
Summarize
the
process
of
fertilization.
Explain
implantation
and
nourishment of the embryo before
development of the placenta.
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Describe
normal
prenatal
development from conception
through birth.
Explain structure and function of
the placenta, umbilical cord, and
fetal membranes.
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Identify
the
potential
of
teratogenic effects during period
of
embryonic
and
fetal
development.
Describe prenatal circulation and
the circulatory changes after birth.
Fertilization
It is the union of ovum
and spermatozoon. It
occurs at the ampulla of
the fallopian tube.
The 23 chromosomes from
the sperm mingle with 23
chromosomes
from
the
ovum, restoring the diploid
number
to
46.
After intercourse, the spermatozoa
ascend and reach the tubes within 30-40
minutes, but they are not able to fertilize
the ovum immediately, and remain 2-6
hours during which they undergo certain
enzymatic change called capacitation
after which they are able to fertilize the
ovum.
Capacitation of the sperm
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Is the process after which the sperm
becomes able to penetrate the zona
pellucida, that surrounding the ovum
and fertilize it.
The cervical and tubal secretions are
mainly responsible for this
capacitation.
Intrauterine development
 Is
divided into three Stages
1. Pre-embryonic Stage
2. Embryonic Stage
3. Fetal Stage
1. Pre-embryonic Stage
 Is
the first 2 weeks after
conception.
 The period from fertilization
through implantation.
Egg surrounded
by sperm. A
sperm penetrates
the egg and
conception
occurs. It is
called a zygote
until it reaches
the uterus in 3-4
days.
Initiation of cell division
 The
zygote divides into 2 cells,
then 4, then 8cells while in the
fallopian tube.
 Up to the 16 cell stage, the cells
become smaller with each
division, it is called a morula
Morula

The outer cells of the morula
secrete fluid, creating a sac of
cell (the blastocyst) that has an
inner cell mass placed offcenter within the sac
The inner cell mass of the
blastocyst develops into the
fetus (embryo).
 The outer layer of blastocyst
cells develops into placenta and
fetal membranes. (trophoblast
the feeding layer)

 The
morula enters the
uterus about 3 to 4 days
after conception, it lingers
in the uterus another 2 to 4
days before beginning
implantation.
 Is
in the secretary phase of
the reproductive cycle, 1½
weeks before the woman
would
be
gain
her
menstrual period.
Complete implantation is a
gradually process that occurs
between the 6 -10 days.
Embryonic structures continue
developing during implantation.
 Immediately after implantation
the endometrium called decidua.
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 Normal
implantation occurs
in the upper site of uterus.
The upper uterus is the best
area for implantation and
placental development for
three reasons:
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The upper uterus is richly supplied
with blood for optimal fetal gas
exchange and nutrition.
The uterine lining is thick in the
upper uterus preventing the
placenta from attaching so deeply
that it does not easily detach after
birth.
 Implantation
in the upper
uterus limits blood loss after
birth because strong figure 8
fibers in this area.
Types of decidua
 Decidua
basalis
 Decidua capsularis
 Decidua parietalis or vera
 Decidual space
Function of the decidua
It is the site of implantation.
 Protection of the uterine wall
against invasion by the chorionic
villi
 Nutrition of the embryo.
 Formation of the placenta
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Second week
Implantation is complete by the
end of the 2nd week.
 The most growth occurs in the
trophoblast, which eventually
become the fetal part of the
placenta.

 The
inner cells mass will
develop into the embryonic
disk
2. Embryonic Stage
Extends from the beginning of
rd
th
the 3 week through the 8
weeks after conception.
 Basic structures of all major
body organs are completed
during the embryonic period.

rd
3
 The
week
embryonic disk develops
three layers (germ layers):
*Ectoderm
*Mesoderm
*Endoderm
*Ectoderm
Brain and spinal cord.
Peripheral nervous system.
Pituitary gland.
Sensory epithelium of the eye, ear, and
nose.
Epidermis, hair, nails.
Subcutaneous glands.
Mammary glands
*Mesoderm
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Cartilage Bone.
Connective & muscle tissue.
Heart, blood vessels, blood cells.
Lymphatic system, spleen, kidneys.
Adrenal cortex, ovaries, testes.
Reproductive system
*Endoderm
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Lining of gastrointestinal &
respiratory tracts.
Tonsils, thyroid, parathyroid, liver,
pancreas.
Lining of urinary bladder and
urethra
Lining of ear canal
The central nervous system
rd
begins developing during the 3
week.
 A thickened flat neural plate
appears, extending toward the
end of the embryonic disk that
will become the head

 Early
heart development
begins beating at 21 to 22
days.
 The neural plate develops
but is still open
th
4
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week
The shape of the embryo changes.
The embryo resembles C-shaped
cylinder by the end of 4th week.
A tail is apparent during the embryonic
period because the brain and spinal
cord develop more rapidly than other
systems
 The
neural tube completes
th
closure during 4 week.
 Formation of the face and
upper respiratory tract begins.
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Beginning of the internal ear and
the eye are apparent.
The upper extremities appear as
buds.
Because the embryo is sharply
flexed the heart is near the embryo
mouth
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The lower respiratory tract begins
growth as a branch of the upper
digestive tract, which is tubular at
this time.
Gradually the esophagus and
trachea separate completely.
th
5
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week
The head is very large because the
brain grows rapidly during 5th week.
The heart is beating and developing
four chambers.
Upper and lower limbs are paddleshaped
th
6
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week
The heart reaches its final four
chambered form.
Upper and lower extremities
continue to become more defined.
The eye continues to develop and the
beginning of the external ear is
apparent.
th
7
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weeks
Extremities become longer and better defind.
The face is now human-looking.
The intestine grow faster than the abdominal
cavity.
The eyelids begin to grow.
The trunk elongates and straightens, although
a C-shaped spinal curve remains at birth.
th
8
 The
weeks
external genitalia begin
to differentiate, but male
and female characteristics
are not distinct until after
the 10th week. 3cm in length
approximately.
 By
th
8
the end of the
week,
all major organ systems
are in place, and many are
functioning in a simple
way.
 Development
of
the
specialized structure is
controlled
by
three
factors:
The genetic information in the
chromosomes received from the
parents.
 Interaction between adjacent
tissue
 And timing

Teratogenic effects
Diagnosed procedures are
prescribed.
 Harmful drugs.
 Inadequate amount of folic acid
before or during pregnancy.
(Effects may cause prenatal damage)
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3. Fetal Stage
Is
begins 9 weeks after
conception and ends
with birth.
9 – 12 weeks
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Fetus approximately 6-8cm in length.
At the beginning of this period, head
is large, about half the total length of
the fetus.
The body begins growing faster than
the head.
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Extremities developed, fingers and
toes differentiated.
External genitalia show signs of
male or female sex.
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The first fetal movement begin but
are too slight for the mother to
detect.
Blood formation occurs primarily in
the liver during the 9th week but
shifts to the spleen by the end of the
12 week.
The
fetus
begins
producing urine during
this period, excreting it
into the amniotic fluid.
13 – 16 weeks
 Fetus
length 9-12 cm
 Weight 110 g. because the
fetus grows rapidly
 Quickening.
 Head
and thorax can be
identified by ultrasound.
 The face looks human because
the eye face forward.
17 –20 weeks
 Fetus
length 19 cm.
 Weight 320 g.
 Heart beat can be heard with
fetoscope.
 Meconium
begins
collecting in bowel.
 This period very rapid
growth.
Fetal
movement
feel
like
fluttering or butterflies.
 Vernix caseosa, fatty, cheese like
secretion of the fetal sebaceous
glands, covers the skin to protect
it from constant exposure to
amniotic fluid.
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 Both
vernix and lanugo hair
diminish as the fetus reaches
term.
 Lanugo hair cover the fetal
body to help the vernix adhere
to the skin.
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Eyebrows and head hair appear.
Brown fat is heat producing fat
deposited on the back of the neck,
behind the sternum, and around
kidneys. Brown fat helps the
neonate maintain temperature
stability after birth.
21 – 24 weeks
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Fetus length 26 cm.
Weight 630 g.
Skin wrinkled and red, vernix present,
head and body covered with lanugo.
The lungs begin to produce surfactant,
make it easier for the baby to breathe
after birth.
25 – 28 weeks
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Fetus length 25-30 cm.
Weight 1000 g.
Eyes partially open, eyelashes
present.
Respiratory system immature, but
fetus may survive if born.
29 – 32 weeks
 fetus
length 32 cm.
 Weight 1700 g.
 Toenails present.
 Body filling out.
Testes descending.
 Iron, nitrogen, calcium stored.
 Vernix covers body.
 Chances of survival improving
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33 – 36 weeks
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fetus length 32-35 cm.
Weight 2000 – 2500 g.
Skin thicker, less wrinkled as
subcutaneous fat accumulates.
Excellent chance for survival.
37 – 40 weeks
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fetus length 36-50 cm.
Weight 3400 g.
Pulmonary system matures.
Lanugo may be present over the
forehead, upper back and upper arms.
Vernix may remain in major creases
such as groin and axillae.
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Testes within scrotum.
Female labia well developed, labia
majora cover labia minora.
Full term ranges from the end of 38 to
40 weeks of fertilization age.
Or 40 to 42 weeks of gestational age.
Because conception occurs about 2
weeks after the first LMP.
Auxiliary Structures
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1.
2.
3.
Three auxiliary structures
developed:
Placenta.
Umbilical cord.
And the fetal membranes
Placenta
A full term placenta is a thick,
disk or circular cake-like shaped
organ.
 The placenta formation begins
at outer layer of the blastocyst,
called the trophoblastic cells.
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Measuring 15-20 in diameter,
about 2.5cm in thickness and 500
grams in weight.
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During in early pregnancy, the
placenta is larger than the fetus.
 The
fetus grows faster than
the placenta, however, so
that the placenta is about
one-sixth the weight of the
fetus at the end of a term of
pregnancy.
Fetal Surface
Is covered with amnion which
is thin smooth membrane.
 The umbilical cord is inserted
in the fetal surface of the
placenta usually near its center.

Maternal Surface
Is dull red in color and is
divided by grooves into 15 – 20
irregular lobes called maternal
cotyledons.
 The maternal surface is partly
covered by a thin grey layer of
deciduas called the basal plate

Function of the placenta
 Metabolic
function.
 Transfer
of
substance
between mother and fetus.
 Endocrine function.
Signs and Symptoms
Pregnancy – 3-8 weeks
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A missing menstrual period
Morning sickness and
nausea
Frequent urination
Uterus is size of a lemon
Breasts enlarge
Fatigue and dizziness
Positive Chadwick’s,
Goodell’s & Hegar’s sign.
Increased vaginal dischrage.
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Woman’s
Nausea usually decreases after 12
weeks.
Uterus is size of an orange.
Palpate above the symphysis
pubis.
Vulva varcosities may appear.
 Woman’s
 Relaxation
of smooth muscles
of veins and bladder increases
the chance of varicose veins
and urinary tract infections.
 Woman is more aware of fetal
movements.
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Woman’s
Fetal movements may be felt at 16
weeks.
Uterus has risen into the abdomen.
Fundus midway between
symphysis pubis and umbilicus.
Urinary frequency decreases.
Blood volume increases.
Uterine souffle heard.
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Woman’s
Skin pigmentation increases: areolae
darken, chloasma and linea nigra
may be obvious.
Colostrum may be expressed.
Braxton Hicks contractions
palpable.
Funds at level of umbilicus at about
20or 24 weeks.
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Woman’s
Heartburn common as uterus
presses on diaphragm and
displaces stomach.
Braxton-hicks contraction more
noticeable.
Lordosis increases, waddling gait
develops due to incresed mobility
of pelvic joints.
Woman’s
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Shortness of breath caused by upward
pressure on diaphragm.
Woman may have difficulty finding a
comfortable position for sleep.
Umbilicus protrudes.
Varicosities more pronounced.
Ankle edema may be present.