Describes stages of prenatal development and effects of teratogens

1. MSc Child Development
STAGES OF
PRENATAL DEVELOPMENT
&
ENVIRONMENTAL INFLUENCE ON
PRENATAL DEVELOPMENT

2. PRENATAL DEVELOPMENT
• A single fertilised egg develops into the complex organism.
• Explosive rate of growth and development which is unparalleled
to any other point in the lifespan.
• Human gestation encompasses period of time from conception
to birth.
• Normal full term birth spans 37-41 weeks of gestation
• Pregnancies that end before 37 weeks – Preterm
• Those that end beyond 42 weeks – post term
(Hetherington et.al 2006)

3. STAGES OF PRENATAL DEVELOPMENT
• Nine months of Prenatal development are characterised in two
ways
• as occurring in three trimesters
• as occurring in three periods
a) the zygote
b) the embryo
c) the fetus

4. GERMINAL PERIOD ( THE ZYGOTE)
• Begins when the fertilised ovum, called the zygote begins to
make its way down the fallopian tube,moving in the direction of
the uterus. (Moore &Persaud,2003 )
• A process of rapid cell division begins as it moves through
fallopian tube.
• By the 4th day, the zygote has multiplied into a ball of more than
50 cells and is called blastocyst

5. GERMINAL PERIOD ( THE ZYGOTE)
• Cells inside blastocyst - embryonic disk – develops into embryo
• Cells on the outside – trophoblast – develops into structure that
support and protect the baby before birth.
• Between 7 and 9 days after conception blastocyst begins the
process of attaching itself to the uterine wall. This is called
implantation.
• Gradually tendrils from the zygote penetrate the blood vessels
in the wall of the uterus
• The zygote forms a physiologically dependent relationship with
the mother.

6. IMPLANTATION

7. GERMINAL PERIOD ( THE ZYGOTE)
• At first the trophoblast multiplies faster to form a membrane
called amnion that encloses the developing organism in the
amniotic fluid.
• Amniotic fluid helps keep the temperature of the prenatal
development constant and provides a cushion against any jolts
caused by the woman’s movement

8. GERMINAL PERIOD ( THE ZYGOTE)
• The inner cell mass differentiates during implantation.
• One layer becomes intestinal system, urinary tract, glands and
lungs.
• Another layer eventually turns into skeltal muscles and
circulatory system.
• A third layer will develop into brain spinal cord and nerves as
well as skin and hair.
• All of this takes place before two weeks.

9. PERIOD OF EMBRYO
• Lasts from implantation through eighth week of pregnancy.
• By the end of second week, cells of trophoblast forms another
protective membrane – chorion which surrounds amnion
• From chorion tiny villi emerges.
• As these villi burrow into the uterine wall, placenta begins to
develop.

10. PERIOD OF EMBRYO
• By bringing mother’s and the embryo’s blood close together the
placenta:
a) permits food and oxygen to reach the
developing organism and
b) waste products to be carried away.
• Placenta is connected to the developing organism through
umbilical cord

11. PERIOD OF EMBRYO
• Umbilical cord first appears as a primitive body stalk and later
grow to a length of 1-3 feet.
• Has one large vein that delivers blood loaded with nutrients.
• And two arteries that remove waste products.

12. PERIOD OF EMBRYO
• Embyonic disc forms three layers:
a) ectoderm – nervous system and skin
b) mesoderm – muscles, skelton, circulatory
system and other internal organs.
c) endoderm – digestive system, lungs, urinary
tract and glands
These three layers give rise to all parts of the body

13. LAYERS OF EMBRYONIC DISC

14. PERIOD OF EMBRYO
• Development of brain.
• The embryonic period is the critical time in the development of
the brain and spinal cord.(Couperus & Nelson,2006)
• Nervous system develops the fastest.
• Ectoderm fold over to form neural tube or primitive spinal cord.
• At 3 ½ weeks the top swells to form the brain.
• Once after brain is formed new cells are created (proliferation)
and migrated to their destination(migration).
• This begins at about 32 days after conception.

15. BRAIN FORMATION

16. PERIOD OF EMBRYO
• While the nervous system is developing, the heart begins to
pump blood.
• Also muscles, backbone, ribs and digestive tract appear.
• During the first month eyes, ear, nose and arms begin to form.
• By the end of fist month the embryo – only ¼ inch long – consist
of millions organised group of cell with specific functions

17. PERIOD OF EMBRYO
• By about 6 weeks of age the embryo begins to look
recognisably human. ( Moore & Persaud )
• The head which was tipped forward begins to move back.
• Head is very large relative to the body.
• The upper body is much larger than the lower part of the body.
• Small arms are visible on which ridges that will become fingers
can be seen

18. EMBRYO - 6 WEEKS OLD

19. PERIOD OF FETUS
• The fetal period begins at 8 weeks after coneption and lasts
until birth. (Moore & Persaud)
• From 8 to 12 weeks the fetus grows to about 3 inches in length.
• Activity levels are high
• By 9 weeks of age the fetus can even hiccup and react to very
loud noice.
• Twelve weeks marks the end of the first trimester

20. BY THE END OF FIRST TRIMESTER

21. PERIOD OF FETUS
• In the second trimester the fetus continue to grow and change.
• In 4th month fetus continues to be very active averaging at least
one movement per minute.
• Also during the second trimester, a fine downy fuss called
lanugo covers the body of the fetus.(Nilsson & Hamberger,
2003)
• The lanugo is coated with a thick whitish cream called vernix
which protects the skin.

22. BY THE END OF SECOND TRIMESTER

23. PERIOD OF FETUS
• The point at which the baby cansurvive, called the age of
viability occurs sometime between 22 and 26 weeks.(Moore &
Persaud, 2008).
• The cerebral cortex enlarges
• Between 30 and 40 weeks the fetus show rhythmic alternation
between sleep and wakefullness.
• Weight increases to an average of 7 – 7 ½ pounds.

24. BY THE END OF THIRD TRIMESTER

25. HIGHLIGHTS OF
PRENATAL DEVELOPMENT (SHAFFER,D.R AND KIPP K , 2007)
Period of Ovum
First 2 weeks • Dividing cluster of cells enters and
moves around the uterus,living off the
yolk of the egg cell
• Blastocyst becomes implanted in the
wall of the uterus, possibly
accompanied by implantation bleeding.

26. Embryonic stage
3 weeks
4 weeks
5 - 8 weeks
• Head and blood vessels form
• Brain begins to develop
• Heart begins to beat and pump blood
• Arm buds and leg buds appear.
• Eyes, ears, nose and mouth form
• Nerves begin to develop.
• Umbilical cord is functional
• Embryo weighs a fraction of an ounce
and is ½ inch long
• Hands and feet develop with webbed
fingers and toes.
• Undifferentiated sex organs appear.
• Teeth buds develop
• Kidneys filter uric acid from blood; liver
produces blood cells
• Bone cells appear
• Head is half the length of the entire body.
• Embryo weighs about 1/13 of an ounce
and is 1 inch long.

27. Fetal stage
9- 16 weeks
13 – 16 weeks
17 – 20 weeks
• All major organ systems are formed
• Fingers and toes are fully formed.
• Eyes can be clearly distinguished.
• Sex of fetus can be determined visually
• Mouth opens and closes; fetus swallows.
• Fetus responds to external stimulation
• Fetus weighs 1 ounce and is 3 inches
long.
• Mother detects fetal movement.
• Many reflexes are present.
• Fingernails and toenails form.
• Head is about one- fourth the length of
the body.
• Hair develops on head

28. 17 – 20 weeks
21- 24 weeks
• Hair develops on head.
• Fine, downy hair (lanugo)covers body
• Fetus sucks its thumb and hiccups
• Heartbeat can be heard when listener
presses head against mother’s abdomen
• Eyes open and shut.
• Light and sounds can be perceived
• Fetus alternates between periods of
wakefulness and sleep.
• Skin looks ruddy because blood vessels
show through the surface.
• Survival rate is low if fetus is born.
• Fetus weighs about 2 pounds and is 14
inches long: Growth rate is slowing down.

29. Third trimester
25- 28 weeks
29 to 36 – 38 weeks
• Organ systems continue to mature.
• Fatty layer begins to develop beneath
skin
• Fetus turns head down in uterus chances
of survival are good if born
• Fetus weighs 3 – 4 pounds and is 16
inches long.
• Organ system function well.
• Fatty layer continues to develop
• Fetal activity level decreases in the
weeks before birth as a result of
crowding.
• Weight increases to an average of 7 – 7
½ pounds ; length increases to about 20
inches.

30. ENVIRONMENTAL INFLUENCE ON PRENATAL
DEVELOPMENT
• During prenatal development environmental factors can
significantly affect the development of the child.
• The term teratogens refers to any environmental agents that
causes damage during the prenatal period.(Berk,2013).
• Teratogens encompasses a wide variety of agents, including
prescription and non-prescription medications and drugs taken
by the mother and environmental toxins such as mother’s age,
her diet and her emotional status will affect the response of both
mother and child to any given teratogen(Hetherington et.al
2006)

32. TERATOGENS’ EFFECT ON PRENATAL DEVELOPMENT
(Friedman & Polifka;1996, Moore & Persaud,1998:Vorhees & Mollnow 1987)
1 A teratogen exerts its effects largely during critical periods.
• The developing organism is most vulnerable during embryonic stage.
• Each organ system developing at its own pace, has a different critical
period (Little,1992).
• Eg. Vulnerable period of heart between 20 and 40 days after
conception.(Friedman & Po.lifka,1996)
• During fetal stage teratogenic effects are seen only on systems that
are still maturing, such as central nervous system and the genitals

33. 2 . Each teratogen exerts certain specific effects.
• Specific patterns of developmental deviation are seen as individual
teratogens influence specific developmental process.
• Eg. Rubella affects mainly the fetus’s heart, eyes and brain.
• The drug thalidomide mainly affects the limbs.
3. Either maternal or fetal genotype may counteract the teratogenic
effect.
• Eg .not all women with rubella produce defective infants.
4 The effect of one teratogen may intensify the effects of another.
Eg: Nutritional deficiencies may intensify adverse effects of drugs that
the mother has ingested.

34. 5.Some teratogens may affect the fetus but have no effect on the
mother.
6. A particular teratogen may produce several defects, whereas
several different teratogens may produce the same deviation.
7. The longer the fetus is exposed to a particular teratogen, the
greater the intensity of the teratogenic effect.
• This is the dose response principle at work .

35. LEGAL AND ILLEGAL DRUGS
• A variety of drugs such as aspirin may have adverse effect on
the fetus.
• For example heavy use of aspirin has been associated with low
birth weights, lower IQ and poor motor control.(Bare, Steissguth,
Darley and Sampson,1990)
• Even non-alcoholic beverages are potentially harmful.
• Studies found that women who drank three or more cups of
coffee a day were at higher risk for miscarriage (Fernandes et.al
1998)

36. NICOTINE AND ALCOHOL
• Researchers have found that both smoking and drinking are
associated with disturbance in placental functioning with
changes in maternal physiology that leads to oxygen deprivation
and thus to potential structural and functional changes in fetus’s
brain
• Sudden Infant Death Syndrome (SIDS) infants under 12 months
of age stop breathing and die without apparent cause, is more
common in the offspring of mothers who smoke , drink or take
narcotic drugs.(Hunt ,2001).

37. SMOKING
• Studies have indicated that passive smoke can also contribute
to low birth weight among the babies of mothers who don’t
smoke
• Passive Smoke cause intellectual and behavioural
developmental delays( Friedman & Polifika,1996).
• Also increased risk of illnesses such as pneumonia, bronchitis,
laryngitis and otitis media. ( Charlton,1994)

38. ALCOHOL
• Fetal Alcoholic Syndrome

39. FETAL ALCOHOLIC SYNDROME
• Movements may be suppressed and young infants often display
motor deficits
• Have a higher incidence of facial, heart and limb defects.
• They are 20 percent shorter than average child of their age and
are often mentally retarded.(Streissgurth 1997)
• They exhibit a wide range of abnormal behaviour.

40. ALCOHOL
• Many infants born to alcoholic mothers show withdrawal from
the drug. They even exhibit symptoms akin to delirium tremors.
• Studies indicate that these children exhibit cognitive deficit, get
lower IQ test scores and have more problems with attention and
academic achievements.

41. ENVIRONMENTAL TOXINS
• Most commonly encountered are radiation, lead, mercury,
herbicides, pesticides, household cleaners, and even food
additives and cosmetics.
• Exposure to lead causes prematurity and low birth weight, brain
damage and physical defects as well as with long term problems
in cognitive and intellectual functioning.
• Effects of certain pesticides are even carried on for generations.

42. ENVIRONMENTAL TOXINS
• Endosulfan tragedy in Kasargod district of Kerala.
• The corporation began aerial spraying of pesticide in its
plantations in the district in 1978 and its application
continued till 2001.
• Children are born with neurobehavioral disorders,
congenital malformations and other abnormalities.
• Surveys showed that the incidence of bone deformities,
infertility, mental retardation and congenital heart disease
in the district was ten times more than the other
population

43. ENDOSULFAN DISASTER.

44. MATERNAL FACTORS
• A woman’s age and parity or the number of children she has had
before may interact in influencing the development of the fetus.
• Women who have their first child when they are under 15 or over 35
are likely to experience more problem during pregnancy and more
complications during delivery than other women.
• Diseases caused during pregnancy can severely affect the developing
fetus.
• Emotional stress in the mother causes problems like sleep
disturbances and irritability even cardiovascular diseases and
diabetes.

45. MATERNAL FACTORS
• Maternal nutrition plays an important role
• The fetus solely depends on the mother for nourishment
• Severe malnutrition can cause serious damage to central
nervous system
• Distort structures of organs like liver, kidneys and pancreas.

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