Prenatal Diagnosis & Genetic Counseling
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Prenatal Diagnosis & Genetic Counseling

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Questions and Answers

What is the time frame for rapid prenatal diagnosis of major aneuploidies using recent techniques?

24-48 hours.

In the context of neural tube defects (NTDs), what is the significance of increased serum alpha-fetoprotein (AFP) levels?

Increased AFP levels indicate a higher likelihood of open neural tube defects.

What are the primary screening methods for detecting structural abnormalities during pregnancy according to the guidelines?

An initial scan at 11-14 weeks and a second scan at around 20 weeks.

What diagnostic test is used to confirm the presence of open neural tube defects following a positive AFP screening?

<p>Amniocentesis for acetylcholinesterase in amniotic fluid.</p> Signup and view all the answers

What is the recurrence risk of neural tube defects if a parent or previous sibling is affected?

<p>5-10%.</p> Signup and view all the answers

What is the primary aim of prenatal diagnosis and genetic counseling?

<p>To identify fetal abnormalities and provide support to parents for informed decision-making.</p> Signup and view all the answers

What distinguishes screening tests from diagnostic tests in prenatal management?

<p>Screening tests are non-diagnostic and used for risk assessment, while diagnostic tests confirm abnormalities in high-risk pregnancies.</p> Signup and view all the answers

What role does cytogenetic analysis play in prenatal diagnostic testing?

<p>Cytogenetic analysis examines fetal cells for chromosomal abnormalities, aiding in diagnosis.</p> Signup and view all the answers

How long does it typically take to obtain results from chorionic villus sampling?

<p>Results from chorionic villus sampling are usually available within 1-2 weeks.</p> Signup and view all the answers

What is the purpose of DNA probing in prenatal diagnosis?

<p>DNA probing is used to identify specific genetic conditions such as sickle cell disease and cystic fibrosis.</p> Signup and view all the answers

What factors might lead parents to opt for termination of a pregnancy based on diagnostic test results?

<p>Parents may choose termination when diagnosed with severe fetal abnormalities or inherited conditions.</p> Signup and view all the answers

What is the significance of the FISH test in prenatal cytogenetic analysis?

<p>The FISH test detects and localizes specific DNA sequences, providing rapid results in cytogenetic analysis.</p> Signup and view all the answers

What are two commonly used invasive diagnostic tests for prenatal analysis?

<p>Amniocentesis and chorionic villus sampling are two frequently employed invasive diagnostic tests.</p> Signup and view all the answers

What is the primary risk factor associated with trisomy occurrences, particularly regarding maternal age?

<p>Maternal advancing age is the primary risk factor for trisomy occurrences.</p> Signup and view all the answers

Identify the three trisomies that are exceptions and do not typically result in first trimester abortions.

<p>Trisomies 13 (Patau), 18 (Edwards), and 21 (Down syndrome) do not typically result in first trimester abortions.</p> Signup and view all the answers

What is the most common inherited cause of male mental retardation, and how is it diagnosed prenatally?

<p>Fragile X syndrome is the most common inherited cause of male mental retardation, diagnosed prenatally by PCR analysis.</p> Signup and view all the answers

Discuss the role of maternal age and history in screening for Down syndrome.

<p>Maternal age above 35 years significantly increases the risk for Down syndrome, warranting further diagnostic testing.</p> Signup and view all the answers

What screening markers are used in the first trimester for Down syndrome diagnosis?

<p>The first trimester screening uses PAPP-A, which is lowered in Down syndrome, and beta-HCG, which is elevated.</p> Signup and view all the answers

How are sex chromosome abnormalities like Turner syndrome and Klinefelter syndrome related to fertility?

<p>Turner syndrome leads to infertility in females, while Klinefelter syndrome results in infertility in males.</p> Signup and view all the answers

Explain why routine screening isn't available for Klinefelter syndrome.

<p>Routine screening for Klinefelter syndrome is not available because the diagnosis is often made incidentally.</p> Signup and view all the answers

What is the typical outcome severity associated with trisomies 13 and 18?

<p>Trisomies 13 and 18 are typically lethal and associated with major structural anomalies.</p> Signup and view all the answers

Study Notes

Prenatal Diagnosis & Genetic Counseling

  • Aim is to identify fetal abnormalities.
  • Parents are reassured by reducing undiagnosed fetal abnormalities.
  • Parents are given information if a fetal abnormality is detected.
  • Parents can make informed decisions about pregnancies with identified abnormalities.
  • Parents at risk for inherited conditions can have healthy children through diagnosis and termination of affected fetuses.
  • Appropriate prenatal management and intrauterine treatment can be provided.

Test for Fetal Abnormality

  • Screening Tests: Non-diagnostic, used to identify pregnancies requiring diagnostic testing.
  • Diagnostic Tests: Performed on high-risk pregnancies identified through screening tests.

Prevalence of Congenital Abnormalities

  • Not explicitly stated in the text.

Prenatal Screening & Diagnostic Tests

  • Cordocentesis: A procedure to obtain fetal blood from the umbilical cord.

Invasive Diagnostic Tests

  • Cytogenetic Analysis: Examines chromosomes in fetal cells obtained through invasive prenatal procedures.
    • Amniocentesis: Takes 2-3 weeks for diagnosis.
    • Chorionic Villus Sampling: Takes 1-2 weeks for diagnosis.
    • Cordocentesis: Takes 24-48 hours for diagnosis.
  • DNA Analysis: Uses fetal DNA for:
    • DNA probing: Detects sickle cell disease and cystic fibrosis.
    • PCR: Detects fragile X syndrome, congenital toxoplasmosis, CMV.
    • Linkage analysis: Detects fragile X syndrome.
    • Biochemical & Enzymatic analysis: Used when DNA analysis is not possible for specific diseases like congenital adrenal hyperplasia and mucopolysaccharidosis.

Cytogenetic Analysis

  • Chorionic Villus Sampling: Cells are already in mitosis, allowing for quicker results.
  • FISH Test: Allows rapid (24-48 hours) prenatal diagnosis of major aneuploidies for chromosomes 13, 18, 21 & XY.

General Process of Steps Required for Preimplantation Genetic Diagnosis and Screening

  • Removal of Blastomere: A single cell is removed from an 8-cell embryo.

Structural Abnormalities

  • Constitute the majority of congenital abnormalities.
  • Screening programs are established for fetal neural tube and cardiac defects.
  • The Royal College of Obstetricians & Gynecologists recommends a two-stage scan for structural abnormalities:
    • Initial scan at booking (11-14 weeks).
    • Scan at or around 20 weeks.

Neural Tube Defects (NTDs)

  • Among the most common major abnormalities.
  • Result from a defect in the formation of the neural tube during embryogenesis.
  • Etiology: Multifactorial, including environmental, genetic, pharmacological, and geographical factors.

Cranial Vault

  • The top part of the skull.

NTD (By USS)

  • Types that affect the cranial vault are present on ultrasound.

Prenatal Screening & Diagnosis of NTD

  • Risk of Recurrence: 5-10% if a parent or previous sibling has had an NTD.
  • Screening Test: Mid-trimester maternal serum alpha-fetoprotein (AFP) levels are increased in pregnancies affected by open NTD types.
  • Diagnostic Test for Open NTD: Acetylcholinesterase is used.
  • Positive AFPs: Cases are referred for amniocentesis to check for acetylcholinesterase in amniotic fluid.

Prevention of NTDs

  • Not explicitly stated in the text.

Congenital Heart Disease (CHD)

  • Etiology: Genetic, environmental, and viral infection.
  • Prenatal Screening is Recommended for:
    • Women with a previous sibling or father affected by CHD (2% risk).
    • Women with two siblings or the mother having CHD (10% risk).
    • Mothers with type 1 diabetes (20% risk).
  • Prenatal Diagnosis:
    • Ultrasound at 20 weeks of gestation.
    • Echocardiography is done in special centers for selected cases.

GIT (Gastrointestinal Tract)

  • Not explicitly stated in the text.

Abdominal Wall Defect - Omphaloceles

  • A birth defect where the intestines stick out through the belly button.

Talipes Equinovarus (Clubfoot)

  • A birth defect where the foot is twisted inward and downward.

Renal

  • Relating to the kidneys.

Others

  • Not explicitly stated in the text.

Chromosomal Abnormalities

  • Aneuploidies: Usually trisomies.
  • Trisomies: Occur due to non-disjunctions in meiosis, often associated with maternal age.
  • Rare Causes of Trisomies: Unbalanced translocations or mosaicism.
  • Majority of Trisomies: Result in first-trimester abortions.
  • **Trisomies 13 (Patau Syndrome), 18 (Edwards Syndrome), & 21 (Down Syndrome): ** Most common trisomies at birth.
  • Trisomies 13 and 18: Lethal due to major structural anomalies (detectable by ultrasound).
  • Screening Program: Required for antenatal diagnosis of Down syndrome, the most common chromosomal abnormality at birth.

Sex Chromosome Abnormalities

  • No relation to maternal age.
  • Turner Syndrome (Monosomy X or 45XO): Infertile females with normal intellect and short stature.
  • Klinefelter Syndrome (47XXY): Infertile males with slightly reduced IQ, testicular dysgenesis, and tall stature.
  • Routine Screening: Not available for these conditions.
  • Diagnosis: Often made incidentally.

Turners Syndrome

  • A genetic condition that affects females.

Klinefelter Syndrome (47XXY)

  • A genetic condition that affects males.

Fragile X Syndrome

  • Most common inherited cause of male mental retardation.
  • Prenatal diagnosis is by PCR analysis, only for male fetus to detect the fragile X gene (FMR1).
  • Prenatal screening is only for families where one parent is known to be a carrier.

Screening Test for Down Syndrome

  • Maternal Age & History: Above 35 years old (risk of 75-80%), offered diagnostic tests.
  • Maternal Serum Biochemistry:
    • First Trimester:
      • PAPP-A is lowered in DS.
      • Beta-hCG is elevated.
    • Second Trimester (15-22 weeks gestation):
      • AFP is increased.
      • HCG is increased.
      • Logarithm predicts individual risk for DS.
      • Not diagnostic but identifies a high-risk group that should be offered diagnostic tests like amniocentesis.

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Description

This quiz explores prenatal diagnosis and genetic counseling, focusing on identifying fetal abnormalities and the tests available for assessment. It also discusses the implications of such diagnoses for parents and the management of risk factors for inherited conditions. Get ready to learn about various screening and diagnostic tests essential for prenatal care.

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