Transcript The Prenatal Environment and Growth

Placental Functions and
Factors Affecting Fetal Growth
Maternal Placental Blood Flow
Intervillous space of mature placenta
contains about 150 ml of blood which is
replenished 3 or 4 times a minute
 Uteroplacental blood flow increases from
– 50 ml per minute at 10 weeks
– 500/600 ml per minute at full term
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Placenta
 Metabolism
 Transfer
 Endocrine
Placental Transfer (gases)
 Oxygen,
Carbon Dioxide,
Carbon Monoxide cross the
placenta by simple diffusion
Placental Transfer (nutrients)
Water freely moves
 No transfer of maternal cholesterol,
triglycerides or phospholipids
 Small amounts of free fatty acids
transported
 vitamins are essential
 Glucose quickly transferred
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Placental Transfer (hormones)
 Protein
hormones do not reach
the fetus, except for the slow
transfer of thryroxine and
triiodothyronine
 Testosterone can cross
Placental Transfer (antibodies)
Some passive immunity is conferred on
the feus by the transfer of maternal
antibodies (mainly gamma globulins)
 diptheria, smallpox and measles
 not whooping cough and chicken pox
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Glucose
Glucose is the primary source of energy
for the fetal metabolism
 Amino acids also required
 Both come from the mother via the
placenta
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Placental Metabolism
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Particularly early in pregnancy,
synthesis of glycogen, cholesterol and
fatty acids
Dizygotic Twins
Dizygotic Twins
Monozygotic
Twins
Monozygotic
Twins
Conjoined Twins
Critical Periods
Since organogenesis occurs primarily in
the embryonic period (weeks 4-8) slight
influences can have drastic and
irreversible effects
 Sensitive periods?
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Congenital Malformations
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Malformations present at birth, irrespective
of cause (genetic or environmental)
Teratogens
 External
agents that cause
congenital malformations
The Six Principles of Teratology
Wilson 1959
Susceptibility to teratogenesis depends on the
genotype of the conceptus and the manner in which
this interacts with adverse environmental factors.
2. Susceptibility to teratogenesis varies with the
developmental stage at the time of exposure to an
adverse influence. There are critical periods of
susceptibility to agents and organ systems affected
by these agents.
1.
The Six Principles of Teratology
Wilson 1959
Teratogenic agents act in specific ways on developing
cells and tissues to initiate sequences of abnormal
developmental events.
4. The access of adverse influences to developing
tissues depends on the nature of the influence.
– nature of the agent
– route and degree of maternal exposure
– rate of placental transfer and systemic absorption
– composition of the maternal and embryonic/fetal
genotypes.
3.
The Six Principles of Teratology
Wilson 1959
5.
There are four manifestations of deviant development
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6.
Death
Malformation
Growth Retardation
Functional Defect)
Manifestations of deviant development increase in
frequency and degree as dosage increases from the
No Observable Adverse Effect Level (NOAEL) to a
dose producing 100% Lethality (LD100).
Teratogens
 Drugs
and medications
 Environmental chemicals
 Ionizing radiation
 Infections
 Metabolic imbalance
Thalidomide
Fetal Alcohol
Syndrome
Fetal Alcohol
Spectrum Disorder
Rubella
Syndrome
Symptoms in the infant may include:
Cloudy corneas or white appearance to pupil, Deafness,
Developmental delay, Excessive sleepiness, Irritability,
Low birth weight, Mental retardation, Seizures, Small
head size, Skin rash at birth, Cardiac Anomalies
Fetal Monitoring
Ultrasonography
Uses reflection of very high
frequency sound waves of between
3.5 to 7.0 megahertz (i.e. 3.5 to 7
million cycles per second)
Monitoring:
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Chorionic sac during
embryonic period
placental and fetal size
multiple births
abnormal presentations
biparietal diameter
Fetal Blood Sampling
Usually from the scalp, fetal blood pH
is a good indicator of placental gas
exchange.
In the past, fetal blood sampling was
used only during labor through the
mother's open cervix to test blood from
the fetal scalp for oxygenation.
Today, in many perinatal care centers, fetal blood sampling is
performed by specially trained perinatologists as part of
diagnosing, treating, and monitoring fetal problems at various
times during pregnancy.
Fetal Blood Sampling
A fetal blood sample may be taken to:
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diagnose genetic or chromosome
abnormalities.
check for and treat severe fetal anemia or
other blood problems such as Rh disease.
check for fetal oxygen levels.
check for fetal infection.
give certain medications to the fetus.
How is fetal blood sampling performed?
A long, thin needle is inserted into the mother's uterus
guided by ultrasound.
Blood may be taken from several sources:
blood vessels of the umbilical cord (also called
cordocentesis, funicentesis, or percutaneous umbilical
blood sampling, or PUBS)
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a fetal blood vessel, usually in the liver or heart
Fetal blood transfusions may also be performed in this way
Amniocentesis
also referred to as
amniotic fluid test or AFT
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used in prenatal diagnosis of chromosomal abnormalities
and fetal infections, in which a small amount of amniotic
fluid, which contains fetal tissues, is extracted from the
amnion or amniotic sac surrounding a developing fetus,
and the fetal DNA is examined for genetic abnormalities.
Little amniotic fluid present prior to 12th week of
gestation
Chorionic Villus Sampling
chromosomal abnormalities etc.
 The advantage of CVS is that it can
be carried out 10-13 weeks after the
last period, earlier than
amniocentesis (which is carried out at
16-20 weeks).
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Alpha-Fetoprotein Assay
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AFP is a glycoprotein synthesized in the fetal liver and
yolk sac.
The fetus normally excretes AFP into its urine, hence
into the amniotic fluid.
High levels may also be present due to:
– open neural tube defect
– open abdominal wall defect
– skin disease or other failure of the interior or exterior
body surface.
– Various forms of tumours
Factors Affecting
Fetal Growth
Placental Insufficiency
 Placental
defects effectively reduce
available surface area
 reduced uteroplacental blood flow
may also occur due to maternal
hypotension or renal disease.
Multiple Pregnancy
 Individuals
of multiple births usually
weigh considerably less
 in the third trimester placenta may
not be able to supply the total
requirements for multiple births
Small Babies
 Low
birth weight:
–
< 2,500g
 Premature:
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< 37 weeks of gestation
 Small for Date:
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Smaller than expected for age