Teratogens
Terminology
• Defn: any environmental agent that
causes damage to the fetus during
prenatal period.
– viruses, drugs, chemicals, and radiation
– others categories?
Terminology
• 95% of all newborns are normal.
Of the remaining 5%,
– 3% have mild, temporary or reversible defects.
– only 2% having continuing effects.
• Effect- What happens- the developmental outcome or
consequence of exposure to a teratogen- variation in the
development of the embryo, fetus, or child.
• Mechanism- How it happens- the physiological or
biological processes that explain the cause or how
specific events occur
Terminology
• Sensitive Period- That broad period of time
when, if an insult occurs, there are likely to be
consequences.
– insults may occur over a broad period of time or in a
number of ways
• e.g., the neurobehavioral effects due to exposure of alcohol
during last trimester)
• Critical Period- A specific period of time during
which, if an insult occurs, a particular
consequence will happen
– Malformation of ears due to thalidomide exposure on
days 34-38 of PND.
Characteristics and Effects of Teratogens
•
Time of exposure
–
Worst effects= period when a body part or organ
system is developing.
When is this?
–
•
Susceptibility to harm varies
–
Not all embryos or fetuses are affected in the same
way by the same exposure.
•
•
•
Characteristics of the fetus influence the effects
Studies with identical twins frequently show that one twin has
impairment from a teratogen while the other doesn’t.
Research on FAS shows that ½ ounce/day can cause
neurobehavioral problems in some children, while some
children born to alcoholic mothers don’t get FAS
Characteristics and Effects of Teratogens
•
Different teratogens can cause the same
defect (equifinality)
–
For example: ADHD may be caused by
•
•
•
chronic stress experienced by the mother during
pregnancy
exposure to drugs during pregnancy
exposure to alcohol during pregnancy
Characteristics and Effects of Teratogens
•
Single teratogen may cause more than 1
defect (multifinality)
–
–
Rubella may cause blindness, deafness,
and mental impairments
Exposure to alcohol may cause physical
malformations, growth retardation, and
mental retardation.
Characteristics and Effects of Teratogens
•
Dose Response (more is worse than less)
–
FAS- Fetal Alcohol Syndrome
•
•
•
–
Associated with heavy drinking throughout pregnancy
physical malformations
may have major mental retardation
FAE- Fetal Alcohol Effects
•
Associated with binge drinking, or occasional drinking- Not
as heavy, not as often
•
Behavioral effects- ADHD, less ability to control emotions
Characteristics and Effects of Teratogens
•
Father’s exposure to teratogens also
increases risk
WHY??????
–
Because sperm take 72 hours to mature and during
this period the sperm are susceptible to
malformations due to environmental exposures
Tetracycline (discolors the enamel of the infant’s
teeth).
–
•
Typically associated with mom, but it is also true if dad
takes it.
Characteristics and Effects of Teratogens
•
Long-term outcomes can be mediated by
postnatal experience
–
–
–
–
Initial effects seem to be more severe
“Effect” may be a susceptibility
Long term high quality care and enriched
environment helps OVERCOME or minimize
bad start
HIV Babies with parents who were drug and
alcohol users did better than non. WHY??
Environmental Teratogens
•
•
What are they?
Methyl mercury- Pollutant found in fish
(very high quantities in some areas of
Japan)
–
–
Increased birth weight  C-Sections
Neurobehavioral effects (ADD, ADHD,
Learning disorder)
Environmental Teratogens
•
Lead Poisoning- found in old paint and
water pipes
–
–
–
Anemia- treatable
Encephalopathy- abnormal development of
the brain & MR
Young children and infants who are lead
poisoned can get MR- Eating the paint off
the walls
Social Drugs
•
Alcohol- 43% of alcoholic mothers have FAS kids
(other 57% have FAE)
–
Full blown FAS:
•
early exposure (specifically days 19-23)- results in facial
dysmorphology- Diagnostic criteria
–
–
–
•
repeated exposure, throughout pregnancy (early/late)
–
–
–
•
wide set eyes (small eyes)
thin upper lip
flat filtrum
microencephaly
mental retardation (mild to severe)
growth retardation (<10% on growth charts)
Late exposure (last trimester)
–
–
–
Decreased birth weight
Hyperactivity
Emotional lability (inability to control emotions/lots of emotional
outbursts)
Social Drugs- Alcohol
•
MECHANISM- How does it work?
–
–
–
–
Mom’s ability to metabolize alcohol is reduced
during pregnancy- decreases as pregnancy
advances
breakdown of alcohol uses extra oxygen- reduces
the amount that is available to the developing
organism- Occurs by collapsing the umbilical cord
Alcohol can cross the placenta which impairs
embryonic and fetal development
Fetus’s ability to metabolize alcohol is 50% of
mom’s (so alcohol remains longer at the end of
pregnancy)
Video- FAE
Social Drugs
•
Smoking (nicotine)
–
Effects
•
•
•
•
•
•
–
Decreased birthweight
Decreased heart rate
Increased carbon monoxide in mom’s system, impairs
oxygen exchange and crosses the placenta- Book study
increased spontaneous abortions
increased perinatal mortality
increased hyperactivity, ADHD, ADD
Mechanism
•
reduced oxygen available to the developing fetus
•
Decreased heart rate and blood pressure
Social Drugs
•
Caffeine- Not as much known. Studies
have conflicting results.
–
–
–
–
Increases heart rate
Increases blood pressure
Constricts blood vessels
Dehydrates, so probably reduces the
oxygen supply
Illegal Drugs
•
Marijuana- small numbers of studiesWHY?????
–
Moms who smoke during pregnancy
•
•
–
Attention may be impaired
babies are smaller
Moms who smoke during pregnancy:
•
•
•
–
have better parent-infant relationship at 1 month of age
have calmer babies
Have better social interactions with the infant
Problem with the internal validity. Why??
•
Self-selected group may have more relaxed view of the
world, so therefore have more “lax” relationship with the
child
Illegal Drugs
•
Cocaine
–
Effects:
•
•
•
•
•
–
–
Decreased gestational age
Pre-term, low birth weight
Placental abruption
Increased rates of birth defects- Malformations of the
heart, CNS, gastrointestinal tract
Increased hyperactivity, ADD at school age.
Mechanism: reduced oxygen supply
Recent study with 300 exposed & 300 nonexposed, controlling for SES found that Low SES
had a greater effect on the infant development than
cocaine.
Low B-W and Gest Age
•
Low birth weight and pre-term birth
–
–
–
Low birth weight= < 2500g or 5.5 lbs
Pre-term birth = < 35 weeks- Not necessarily bad
Influences on the size of the infant
•
•
•
•
•
•
Mother’s ht, wt
Mother’s age
Mother’s weight at birth
Environmental variables
Nutrition
Birth order
Birth weight
Babies BW
14
40
Maternal Age (in years)
• <14 or >40, increased risk
Gestational weight, Birth weight,
and Survival
Low Birth weight & survival
Weight at birth
1 – 1 ½ lbs
1 ¾ - 2 lbs
2 ¼ - 3 lbs
3 – 3 ½ lbs
>5 ½ lbs
Pre-term birth & survival to 1 year
Gestational age @ birth
<24 weeks
24-25 weeks
26-29 weeks
30-32 weeks
33-36 weeks
37-40 weeks
41+ weeks
% survival
33%
67%
84%
91%
98%
35%
63%
86%
93%
98%
99.3%
99.4 %