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Questions and Answers
What is the primary purpose of ultrasonography during pregnancy?
Which diagnostic method is considered to be the quickest for determining genetic abnormalities?
What is a significant risk associated with Chorionic Villus Sampling (CVS)?
Which biochemical marker is commonly assessed in maternal serum screening to indicate fetal abnormalities?
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What type of sampling is performed in cordocentesis (PUBS)?
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How does Noninvasive Prenatal Screening (NIPS) function?
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Which statement about amniocentesis is accurate?
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What does maternal serum screening require after positive results?
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What is the typical result of a balanced translocation between chromosome 21 and chromosome 14?
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Which condition is characterized by cri du chat syndrome due to a chromosomal deletion?
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What percentage of birth defects is attributed to gene defects?
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Which environmental agent is known to be a teratogen that can induce birth defects?
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What method is commonly used for diagnosing Fragile X syndrome?
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Achondroplasia is a genetic disorder resulting from a mutation in which chromosome?
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What type of chromosomal alteration results in ring chromosomes?
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What type of genetic disorders manifests only in homozygous individuals?
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What is the term used to describe maternal factors that can cause birth defects?
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Which birth defect is most commonly linked to poorly controlled maternal diabetes?
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During which weeks post-fertilization is the fetal brain considered most vulnerable?
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What is a common result of oligohydramnios in fetal development?
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What dietary management approach can help infants at risk of defects associated with phenylketonuria?
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Which of the following conditions can result from multifactorial inheritance?
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What mechanism can lead to intrauterine amputations during fetal development?
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Which type of inheritance involves interactions between multiple genes and environmental factors?
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Study Notes
Ultrasound
- Uses high-frequency sound waves to create images of the fetus and surrounding structures.
- Performed transabdominally or transvaginally.
- Can reveal fetal age, growth, congenital anomalies, amniotic fluid volume, placental position, and multiple gestations.
- Crucial for planning pregnancy management, especially in low-birth-weight cases.
- Measurements like crown-rump length, biparietal diameter (BPD), femur length, and abdominal circumference assess fetal development.
Amniocentesis
- Involves inserting a needle transabdominally into the amniotic cavity to retrieve 20–30 mL of fluid.
- Typically performed after 14 weeks of gestation.
- Detects chromosomal abnormalities and genetic markers with high accuracy.
- Results take 1–2 weeks.
- Advances in molecular biology, including PCR, have improved detection of genetic abnormalities.
Chorionic Villus Sampling (CVS)
- Involves collecting cells from the placental tissue.
- Performed transabdominally or transvaginally.
- Allows for early genetic testing (results in 2–3 days).
- Carries a slight risk of limb reduction defects, particularly affecting the digits.
Cordocentesis (PUBS)
- Conducted after the 14th week.
- Involves sampling fetal blood from the umbilical cord.
- Diagnoses hematological diseases and chromosomal anomalies.
- Carries a slightly higher risk of fetal loss than amniocentesis.
- Generally reserved for high-risk cases.
Maternal Serum Screening
- Assesses maternal blood for biochemical markers, such as alpha-fetoprotein (AFP), which can indicate fetal abnormalities.
- Useful in the second trimester.
- Requires confirmatory tests, such as amniocentesis, for positive results.
Noninvasive Prenatal Screening (NIPS)
- Detects fetal DNA circulating in maternal blood as early as 4–6 weeks post-conception.
- Techniques like FISH and PCR help identify genetic anomalies, including trisomies.
- High predictive accuracy but used only for screening.
- Invasive tests are required for confirmation.
Deletion
- A chromosome breaks and loses part of its structure.
- Causes cri du chat syndrome (partial terminal deletion on the short arm of chromosome 5), characterized by a cat-like cry, microcephaly, severe mental deficiency, and congenital heart defects.
Ring Chromosome
- Forms when both ends of a chromosome are lost and the ends rejoin to create a ring shape.
- Can occur with any chromosome.
- Observed in conditions like Turner syndrome (45,X) and trisomy 18 (Edwards syndrome).
Duplications and Inversions
- Parts of chromosomes can be duplicated or inverted during meiosis.
- These conditions may result in syndromes similar to those seen after the nondisjunction of entire chromosomes.
Birth Defects Caused by Mutant Genes
- Approximately 7% to 8% of birth defects are attributed to gene defects.
- A mutation is a permanent, heritable change in the DNA sequence.
- Most mutations are detrimental or lethal.
- The rate of mutations can increase due to environmental factors, such as high doses of ionizing radiation.
Key Genetic Disorders
- Achondroplasia - Dominantly inherited condition resulting from a specific mutation in the fibroblast growth factor receptor 3 gene on chromosome 4p.
- Congenital Suprarenal Hyperplasia and Microcephaly - Examples of autosomal recessive defects.
Fragile X Syndrome
- The second most common inherited cause of moderate intellectual disability.
- Diagnosis involves chromosome analysis or DNA testing for CGG nucleotide expansions in the FMR1 gene.
Birth Defects Caused By Environmental Factors
- Human embryos are vulnerable to teratogens—agents capable of inducing birth defects or increasing their prevalence.
- The CNS is particularly affected by teratogens.
- Studies from Japanese atomic bomb survivors indicate that the brain is most vulnerable between 8 to 16 weeks post-fertilization.
Maternal Factors as Teratogens
- Maternal factors like diabetes and phenylketonuria can act as teratogens.
- Poorly controlled maternal diabetes increases the risk of spontaneous miscarriages, brain anomalies, skeletal defects, and congenital heart issues.
- Infants of diabetic mothers are often large and face various metabolic complications.
- Phenylketonuria increases the risk of microcephaly, cardiac defects, and mental deficiency in offspring if not managed.
- A phenylalanine-restricted diet can help prevent these complications.
- Low levels of folic acid and vitamin B12 in mothers increase the risk of neural tube defects.
Mechanical Factors as Teratogens
- Reduced quantity of amniotic fluid (oligohydramnios) can cause deformations in the fetus.
- These deformations include limb abnormalities like hyperextension of the knee, congenital hip dislocation, and clubfoot.
- These issues may arise from prolonged fetal compression due to restricted mobility or a malformed uterus.
- Intrauterine amputations or other anomalies can occur due to amniotic bands.
Birth Defects Caused By Multifactorial Inheritance
- Involve interactions between multiple genes and environmental factors.
- Common defects include cleft lip, cleft palate, neural tube defects (e.g., spina bifida), pyloric stenosis, and congenital dislocation of the hip.
- New research supports a "multiple genes of variable expression" hypothesis, indicating that a few specific genes, interacting in various ways, likely contribute to the development of these conditions.
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Description
This quiz covers key prenatal diagnostic techniques such as ultrasound, amniocentesis, and chorionic villus sampling (CVS). Participants will learn about the methods, purposes, and outcomes of these procedures, which are critical for monitoring fetal health and detecting potential anomalies. It's essential knowledge for anyone interested in maternal-fetal medicine.
