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Section 1. Prenatal development stages

Pediatric Optometry
Section 1:
Overview of a normal child
Prenatal development :
• Prenatal stages
• Germinal
• Embryonic
• Foetal
• Embryology
• Genetics
• Mendellion mode
• Multifactorial mode
• Chromosomal aberrations
• Prenatal and environmental influences on foetus
• Teratogens
Prenatal – Before birth
Perinatal – Circumstances around birth
Postnatal – After birth
• Oocyte is released from the ovary and begins its way down the
fallopian tube.
• Sperm enters the female reproductive track.
• About 300 000000 sperm cells enter the female reproductive system
but only 1% make it through the uterus to the fallopian tubes (10
• One sperm penetrates the oocyte through the zona pellucida.
• A zygote is formed after the sperm and ovum is joined.
• The first 2 weeks after
• Week 3 to 8 weeks after
• Week 9 to 40 after conception
(Week 0-2)
• Time frame from conception
⃕ implantation.
• The fertilized egg becomes a zygote 10 days after
• Time of rapid cell division – begins 24-36 hours
after conception.
• Divide into two distinctive masses
• Outer cells – placenta
• Inner cells - embryo
(Week 0-2)
(Week 0-2)
• Rapid cell division and cells are now known as
blastocyst (Zygote ➞morula➞blastocyst).
• Blastocyst
• Ectoderm
➠ skin and nervous system
• Endoderm ➠ digestive & respiratory
• Mesoderm ➠ muscle & skeletal
• Implantation: Blastocyst arrive at uterus &
attached successfully
(only 58% success of natural conceptions implanted)
(week 3 - 8)
• The beginning of week three after conception.
• Rate of cell division intensifies, support systems
organs begin to form.
• Blastocyst becomes an embryo.
• Masses of cells becomes a distinct human being.
• Sources of nutrition & protection develops:
• Amniotic sac
• Placenta
• Umbilical cord
Amniotic sac & fluid
• Amniotic sac: Thin but tough transparent fluidfilled membrane that encloses the developing
embryo and later the fetus.
• Inner membranes (amnion): Encloses the amniotic
cavity and contains the amnionic fluid produced by the
• Outer membranes (chorion):contains the amnion and
form part of the placenta.
Functions of the amnionic fluid
• Regulates temperature : It helps keep the baby warm.
• Provides lubrication preventing the baby's body parts
from growing together.
• Enables the baby to move easily to exercise muscles and
strengthen bones before being born.
• Acts like a liquid shock absorber for the baby by
distributing any force that may push on the mother's
Clinical significance of Amnionic
sac and fluid
• Chorioamnionitis:
Inflammation of amnionic sac and can result in neonatal
• Amniocentesis:
Procedure where a sample of the amnionic fluid is taken
in prenatal diagnosis of chromosomal abnormalities and
fetal infection
• A disk-shaped mass of tissue:
• Fetal placenta – develops from
• Maternal Placenta – develops from
maternal uterine tissue.
• It forms along the wall of the
Placenta: Functions
• Nutrition:
• Active and passive transport through which the embryo receives
nutrients and oxygen
• Excretion:
• Wastes (urea, uric acid & creatinine) from the fetus are discharged in
the placenta
• Immunity:
• IgG antibodies can pass through placenta
• Barrier against some microbes
• Endocrine function:
• hCG (Human chorionic gonadotropin)
• Progesterone
• Estrogen
• Cloaking from mother’s immune system
• To evade the attack from mother’s immune system
Placenta: Clinical significance
• Placenta accreta:
• When placenta implants too deeply
• Placenta praevia:
• When placenta blocks the cervix
• Placenta abruption:
• Premature rupturing of the placenta
• Placentitis:
• Such as STORCH infections
• Chorioamnionitis:
• Intra-amniotic infection
Umbilical cord
• It is the ‘rope’ of tissue connecting the placenta to the embryo; (45-60
cm long)
• this rope contains two fetal umbilical arteries - and one umbilical vein
• The umbilical vein supplies the fetus with oxygenated nutrient rich
• The fetal heart pumps deoxygenated, nutrient depleted blood back to
the placenta.
• Umbilical cord stem cells are often harvest that have the ability to
regenerate cells such as bone cartilage and muscle
• At the 3rd week the neural tube
that becomes the spinal cord
begins to form.
• At 21 days eyes begin to appear,
@ 24 days cells for the heart
begin to differentiate.
• Embryo vulnerable to
environmental changes.
Embryonic – 4 weeks
• At 4 weeks arms and leg buds
• embryo between 5 – 7 mm
• Optic vesicle has fully invaginated.
• Cerebral hemispheres are already
• Heart starts to develop and brain
areas start to differentiate.
Embryonic – 5 weeks
• Brain is larger in relation to rest
of body.
• Structural differentiation.
• The heart starts to change
from tube to 4-chambered
• Eyes recognizable behind lids.
• Completion of thorax and
pelvic development.
Embryonic – 6 weeks
• Retina starts to
• 6 ½ weeks the lens and
cornea forms.
• Nerve channels and
muscles link - thus
primitive movements
start to appear.
Embryonic– 7 weeks
• Primitive tonic responses to
changes in position.
• “Righting” reactions present.
Semicircular canals of labyrinth
functional when embryo floats in
a fluid sphere contained by the
amniotic membrane.
• Embryo is essentially complete.
• Testes and ovaries already
Embryonic – 8 weeks
• Length & weight of embryo: 1.6 cm and 1 g
• Basic form of the skeleton completed
(mainly cartilage)
• Face definitive form (mouth, ears, eyes).
• Eye muscles and lids start to form
• Eyes are moving in from their lateral
• Overt movements present due to tonic
capacity of muscles.
• Fingers and toes are forming.
FETAL PERIOD (Week 9 – 40)
• Cell differentiation mostly complete.
• Further development of established
embryonic structures.
• Lasts from the beginning of the third
month until birth.
• Increase in size & weight
• At the beginning of this stage (9 weeks)
Fetus ways 2 g and is 2.3 cm long.
• By far the longest period of prenatal
Fetal period cont.…
• Fetus is very active, moving its arms, legs, opening and
closing mouth & moving head.
• Organs, limbs, muscles and systems become functional.
• Fetus begins to kick, squirm, turn its head and eventually
turn his/her body.
Fetal – 3 months
• Length & weight of fetus: 5.4 cm and 14 g.
• Connection between nervous system and
• On stimulation at the corner of the mouth
long muscles of the neck and trunk contract
contra laterally.
• Contractions of the body.
• Fetus can in/exhale amniotic fluid.
• Hair forming on head.
• Taste buds and vocal chords develop.
Fetal -3 months
• Stimulation of the palm elicits
extension of the wrist and
fanning of the fingers.
• Arms and hands have rotated
that the palms now face each
Fetal -3 months
• Eye lids closed, but oculo-motor
muscles undergo innervation and
movement of the eye ball is visible.
• Lids sealed shut around 9 weeks and
remains closed until 26 weeks.
• Iris starts to develop, although eyes are
still on side of head.
• 3 ½ months = eye brows start to form.
• By 15 weeks body covered with lanugo
to protect the skin.
• Hearing improves and the fetus may
respond to loud noises/sounds.
Fetal – 4 months
• Beginning of Second trimester.
• Length & weight of fetus: 11.6 cm and 100 g.
• Face human appearance.
• Thumb sucking, hick-ups and all reflexes are present
except for vocal responses and functional breathing.
• Can swallow.
• Head movement shows signs of differentiation.
• Heart beats can be heard with stethoscope (120 – 160
beats per minute).
• Eyes in final position.
• At 18 weeks can experiments shows that fetus can
distinguish between heartbeat and voice.
Fetal – 5 months
• Length & weight of fetus: 25.6 cm and
300 g.
• Mother strongly aware of movement.
And definite awake/sleep cycles
• Optic nerve has a million fibers of which
90% reach the cortex via the LGN
(mediation mechanism for the macula).
• Eyebrows and scalp hair appear by end
of 20 weeks.
Fetal – 5 months cont…
• End of 5 months well advanced in its
• 5 1/2 months = development of fovea
• fovea and optic nerve head is now in
relation, the distance that it will be in in
an adult eye.
myelination of nervous system starts.
5½ moths if carrying a girl ,her body has already produced all the
eggs her ovaries will contain
Fetal – 6 months
• Length & weight of fetus: 30 cm and 600 g.
• Eyes completely formed and eye lids start
to open and close by week 26.
• Can see light and dark.
• Lungs develop and become capable of
• May suck its thumb and other reflexive
behavior present such as swallowing and
Footprints and fingerprints develop.
Skin is protected by waxy substance called vernix.
Fetal – 7 months
• Beginning of third trimester.
• Length & weight of fetus: 37.6 cm
and 875 g.
• Retina almost adult arrangement.
• Historical border between surviving
or dying.
• Ears completely developed, can
hear voices and music.
• Most babies start to rotate to a head
down position to get ready for the
birth process
Fetal – 8 months
• Length & weight of fetus: 42.4 cm and 1 700 g.
• Fat layers under skin forms to protect fetus against temperature
changes during birth.
• Can pick up breathing problems, problems with temperature
control and weight loss if born now
• Heart rate faster.
• Fetus changes position
• Survival estimated at 75- 90% from 32weeks.
Fetal – 9 months
• 40 weeks / 9 month is normal
• Length & weight of Fetus by
the time of birth is 51.2 cm and
3500 g.
• The lungs of the fetus are
mature and ready to enter the
real world.
Video – Miracle of Life
(12 min)
• https://www.youtube.com/watch?v=GZk4hT7ncv0