Placental Functions and Factors Affecting Fetal Growth

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Placental Functions and Factors Affecting Fetal
Growth
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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

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Placental Transfer (gases)

• Oxygen, Carbon Dioxide, Carbon Monoxide cross the
  placenta by simple diffusion

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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

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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

• Particularly early in pregnancy, synthesis of
  glycogen, cholesterol and fatty acids

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Dizygotic Twins
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Dizygotic Twins
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Monozygotic Twins
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Monozygotic Twins
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Conjoined Twins
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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

• Malformations present at birth, irrespective of
  cause (genetic or environmental)

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Teratogens

• External agents that cause congenital
  malformations

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The Six Principles of TeratologyWilson 1959

• Susceptibility to teratogenesis depends on the
  genotype of the conceptus and the manner in which
  this interacts with adverse environmental
  factors.
• 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.

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The Six Principles of TeratologyWilson 1959

• Teratogenic agents act in specific ways on
  developing cells and tissues to initiate
  sequences of abnormal developmental events.
• 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.

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The Six Principles of TeratologyWilson 1959

• There are four manifestations of deviant
  development
• 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).

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Teratogens

• Drugs and medications
• Environmental chemicals
• Ionizing radiation
• Infections
• Metabolic imbalance

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Thalidomide
Fetal Alcohol Syndrome Fetal Alcohol Spectrum
Disorder
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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

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Fetal Monitoring
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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
• Chorionic sac during embryonic period
• placental and fetal size
• multiple births
• abnormal presentations
• biparietal diameter

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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.
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Fetal Blood Sampling

• A fetal blood sample may be taken to
• 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.

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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)
• a fetal blood vessel, usually in the liver or
  heart
• Fetal blood transfusions may also be performed in
  this

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Amniocentesis
also referred to as amniotic fluid test or AFT

• 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

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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

• 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

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Factors Affecting Fetal Growth
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Placental Insufficiency

• Placental defects effectively reduce available
  surface area
• reduced uteroplacental blood flow may also occur
  due to maternal hypotension or renal disease.

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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

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Small Babies

• Low birth weight
• lt 2,500g
• Premature
• lt 37 weeks of gestation
• Small for Date
• Smaller than expected for age