1. Fetal development occurs in three main stages - the pre-embryonic period from weeks 1-2 where rapid cell multiplication occurs, the embryonic period from weeks 3-8 where major organ systems develop, and the fetal period from weeks 9 until birth where the fetus continues to grow and develop. 2. During the pre-embryonic period the zygote travels through the fallopian tube and undergoes cell division, and in the embryonic period the major organs begin to form. 3. In the fetal period from months 3-9 the fetus continues to develop and grow, with all essential external and internal structures present by the end of the embryonic period, and the fetus gaining weight and length throughout

1. FETAL DEVELOPMENT
Introduction
 Embryology is the study of development from the
fertilized egg through the 8 weeks
 Fetal period begins 9 to till birth during these time
developing human is called fetus.
Intrauterine Development
Two main phases are:
 1. Cellular multiplication
 2. Implantation
Cellular Multiplication
 The fertilized zygote begins its travel through the
fallopian tube toward the uterus.
 Cell / mitotic division (cleavage) occurs
 Morula eventually forms a fluid filled cavity within the
cell mass.
 Inner solid cell mass is called Blastocyst
 Outer cell mass that surrounds the cavity is the
Trophoblast
Development
Stage 1 – Pre-embryonic/Ovular period
 Weeks 1 - 2
Stage 2 -- Embryonic
 Weeks 3 - 8
STAGE 3 -- FETAL
 Weeks 9 - 40
Pre-embryonic Period
Weeks 1-2
 Traveling in the fallopian tube where rapid cellular
multiplication and differentiation occurs.
 The establishment of the embryonic membranes and the
germ layers (germinal period).
 Groove formed along middle of the back for the neural
tube.
Embryonic Period
Weeks 3-8
 Anterior end of neural tube closes
 to form the brain and the posterior
 end closes to form the spinal cord
 Heart begins to beat
 Eyes appear
 Limb Buds for arms
 and legs
 CR = 4 mm
Week 5
 Head grows larger
 Primitive heart tube is forming. Vasculature begins to
develop in embryonic disc.
 A notochord forms in the center of the embryonic disk
 Hand and feet plates develop
 Facial features begin to develop
 CR = 8 mm.
Week 6
 Fetal circulation is established
 Chambers form in the heart
 Upper lip and palate start fusing
 Eyes move to front of face
 Fingers are webbed
 External ear develops
Week 7
 Eyelids start to form
 Fingers develop; elbows visible
 Diaphragm separates
 abdomen from chest
 Bronchi develop
 Arms and legs move
Week 8
 Fingers and toes distinct
 Skeletal ossification begins
 Testes and ovaries are
 distinguishable
 Heart has four chambers
 Circulation through
 umbilical cord occurs
 *** ALL essential external and internal structures are
present and now will continue to grow
The Zygote—Month 1
 Fertilized egg reaches the uterus and attaches itself to
the uterus.
 Cell multiplication begins
 Internal organs and circulatory system begins to form.
 Cell Division takes place and at the end of two weeks
the zygote is the size of a pin-head
 Heart begins to beat
 Small bumps show the beginnings of arms and legs
The Embryo—Month 2
 At 5 weeks the embryo is ¼ inch long
 All major organ systems develop
 The placenta and Umbilical Cord develop
 Placenta- The tissue that connects the sac around the
unborn baby to the mother’s uterus
 Umbilical Cord- Tube that connects the baby to the
placenta
 Brings the baby nourishment and oxygen from the
mother’s blood
 Takes away waster products
 Amniotic Fluid surrounds the baby
 Face, and limbs take shape
The Fetus—Month 3
 The fetus is about 1 inch long
 Nostrils, mouth, lips, teeth buds, and eyelids form
 Fingers and toes are almost complete
 Arms, legs, fingers, and toes have developed
 All internal organs are present—but aren’t ready to
function
 The genital organs can be recognized as male or female
Weeks 9-12- 3rd
month
 Head size increases
 Nails appear
 Eyelids appear and close and fuse shut
 Kidneys excrete urine
 Intestines are forming; peristalsis begins
 Heartbeat can be heard via ultrasound
The Fetus—Month

2.  Fetus is 3 inches long and weights 5 oz.
 Baby is covered with a layer of thick, downy hair called
lanugo.
 Heartbeat can be heard clearly.
 The baby can such thumb, swallow and hiccup.
Weeks 13-16- 4th
month
 Lips form, facial contour develops
 Ossification of bone begins
 Meconium begins to form in the intestines
 Hair present on scalp
 Sex can be determined visually
The Fetus-Month 5
 The Fetus is about 6 inches long and weighs 4-5 oz.
 A protective coating called vernix begins to form on
baby's skin.
 Hair eyelashes and eyebrows appear
 Organs keep maturing
 Fetus is very active
 The eyes can open and blink
Weeks 17-20 -5th
month
 Hair abundant on head
 Lanugo covers the body
 Myelination of spinal cord begins
 Suck and swallow begin
 Quickening occurs ~ 18 weeks
The Fetus—Month 6
 The fetus is 8-10 inches long and weighs 4-5 oz.
 Your baby's lungs are filled with amniotic fluid, and he
has started breathing motions.
 If you talk or sing, he can hear you.
 Fat is starting to deposit under the skin
Weeks 21-24- 6th
month
 Respiratory movement with air sacs formed
 Surfactant production begins ~ 24 weeks
 Brain appears mature
 Eyebrows and eyelashes
 can be seen
 Reacts to sudden noise
 with active movement
The Fetus—Month 7
 Fetus is 10-12 inches long and weighs about 1-2
pounds.
 Fetus is active and then rests.
 The baby now uses the four senses of vision, hearing,
taste and touch
Weeks 25 – 28- 7th
month
 Eyelids open and close
 Capillaries proliferate around the lungs’ alveoli making
gas exchange possible
 Skin has wrinkled red appearance
 Rapid brain development
The Fetus—Month 8
 The fetus is 14-16 inches long and weighs 2-3 pounds
 Layers of fat are piling on.
 Fetus has probably turned head-down in preparation for
birth.
 Fetus may react to noises with a jerking action
Weeks 29- 32- 8th
month
 Subcutaneous fat forms
 Testes start descending
 Fingernails and toenails are complete
 Bones are fully developed, but still soft and pliable
The Fetus—Month 9
 Fetus is about 17-18 inches long and weighs 5-6 pounds
 Skin is smooth because of the fat
 Baby’s movement slows down due to lack of room
 “Lightening” occurs when the baby drops in the pelvis
 Disease fighting antibodies are taken from the mother’s
blood
Weeks 33-36- 9th
month
 Lanugo begins to disappear.
 Fingernails reach the end of the fingertips.
 A baby born at 36 weeks has a high chance of survival,
but may require medical interventions.
Weeks 37 to 40
 The fetus is considered full-term at the end of the 39th
week of gestational age.
 It may be 48 to 53 cm (19 to 21 inches) in length.
 The lanugo is gone except on the upper arms and
shoulders.
 Fingernails extend beyond fingertips.
 Small breast buds are present on both sexes.
 Head hair is now coarse and thickest.
The development is continued postnatally with
adaptation to extrauterine life and child
development stages
Nutrition
The fetus passes through 3 phases of acquisition of nutrition
from mother:
 Absorption phase: Zygote is nourished by cellular
cytoplasm and secretions in fallopian tubes and uterine
cavity.
 Histoplasmic transfer: After nidation and before
establishment of uteroplacental circulation, fetus
nutrition is derived from decidual cells and maternal
blood pools that open up as a result of eroding activity
of trophoblasts.
 Hematotrophic phase: After third week of gestation,
substances are transported passively via intervillous
space.
Functions of the Placenta
 Fetal Respirations
 Fetal Nutrition
 Endocrine Functions
 Elimination of Wastes
 Barrier against certain substances