THE CRITICAL THE CRITICAL PERIODS AND PERIODS AND TERATOGENICSTERATOGENICS

Critical PeriodsCritical PeriodsThe critical periods are times during

which certain environmental influences can have an impact on the development of a child.

The most likely time for a miscarriage, or spontaneous abortion, is in the first three months, as the organs are forming and first becoming functional.

15-20% end in miscarriage

Definition of TeratogenicsDefinition of TeratogenicsAny agent that causes a birth

defect (from the Greek word teras meaning ‘monster’)

Includes drugs, chemicals, viruses – any substance or factor that can cause a defect.

The Thalidomide DisasterThe Thalidomide Disaster

Early 1960sPrescribed as sedative to

control nausea4th-6th weeks –

abnormalities. Fused fingers and toes,

dislocated hips, missing limbs, hands and feet attached to torso, facial malfunctions, malformed organs.

10, 000 children worldwide before detection.

Effects of teratogenic agents Effects of teratogenic agents on prenatal developmenton prenatal development1) Sensitive periods: Varies with organ systems

developing at different times. Germinal period - zygote may

be completely destroyed.Embryonic period –most

vulnerable in structural abnormality

Foetal period – more likely function than structure.

2) Tissue-specific effectEach teratogen acts in a specific

way on specific developing tissue E.g. thalidomide – limb

deformation, while mercury causes brain damage.

3) Dose-response relationship* > concentration of teratogenic =

> risk of abnormal development

4) Individual differences in effect

Response depends to some degree on its genotype and that of its mother.

Mother’s age, nutrition, hormonal balance can all affect the action of teratogens

Influences and EffectsInfluences and EffectsMalnutritionDrug and alcohol intakeIllnessesExternal environmental hazards

MalnutritionMalnutrition

Higher chance of premature or low-birthweight infants

Affects developing brain – can contain as few as 60% of normal number of cells

Major concern for low socio-economic families

Drug IntakeDrug IntakeDrugs can cross the placentaStrongest effect in early

pregnancyIdeally no medication should be

prescribed for pregnant or breastfeeding women unless it is absolutely essential for her health or that of her child.

Drug Effects

Aspirin Increased risk of bleeding for mother and baby; harm to circulatory system

Oral contraceptives

Increased risk of birth defects

Marijuana Irritability, nervousness, tremors; easily disturbed, startles

Alcohol Foetal alcohol syndrome (FAS) – mental retardation, delayed growth, facial malformation; learning difficulties, smaller head

Opiates Likely to bear premature babies addicted to the drugs in the womb

Nicotine Miscarriage, low birth weight, stillbirth, short stature, mental retardation, learning disabilities

Caffeine Miscarriage, low birth weight

Cocaine Decreased height, low birth weight, respiratory problems, seizures, learning difficulties; addiction

IllnessesIllnessesDisease producing organisms in the

mother’s blood can sometiems infect the foetus via the placenta

Minor effects on the mother can still have serious effects on the foetus.

E.g. rubella can cause blindness, deafness or heart disease in the foetus in first four weeks of pregnancy

Other diseases that can be transmitted include: chicken pox, mumps, malaria, syphilis, herpes and AIDS.

External Environmental External Environmental HazardsHazardsRadiation – gene mutations,

higher incidence of cancers, physical deformities

High temperatures – increased chance of neural tube defects, such as spinal bifida