This document discusses prenatal diagnosis techniques such as amniocentesis and chorionic villus sampling. Amniocentesis obtains amniotic fluid containing fetal cells for analysis, while chorionic villus sampling collects placental tissue for direct analysis. Both techniques carry small risks but can diagnose chromosomal abnormalities and genetic disorders. The document also outlines the purposes, indications, procedures, advantages, and disadvantages of these important prenatal diagnostic methods.

1. PRENATAL DIAGNOSIS-
AMNIOCENTESIS
AND
CHORIONIC VILLUS SAMPLING
M MRIDHUNA MANOHARAN
M.Sc. BIOTECHNOLOGY

2. The goal of prenatal diagnosis is not to generate perfect
babies.
“There are no perfect human specimens – we are all
genetically flawed in some way.”
-F.Collins

3. INTRODUCTION
 Prenatal Diagnosis is the process of determining foetal
anomalies or genetic disorders, to provide expecting parents
with information and the opportunity to modify pregnancy
management and/or postnatal care.
 Screening of foetus for gross chromosomal aberrations (
polyploidy, aneuploidy, deletions, translocations) and sex
prediction.
 Without knowledge gained by prenatal diagnosis, there could
be an unfavourable outcome for the foetus or the mother or
both.
 Congenital anomalies account for 20-25% of perinatal deaths.

4. PURPOSES OF PRENATAL
DIAGNOSIS
Prenatal diagnosis is helpful for :
 Managing the remaining weeks of the pregnancy.
 Determining the outcome of the pregnancy.
 Planning for possible complications with the birth process.
 Planning for problems that may occur in the newborn infant.
 Deciding whether to continue the pregnancy.
 Finding conditions that may affect future pregnancies.

5. INDICATIONS OF PRENATAL
DIAGNOSIS
 ADVANCED MATERNAL AGE
 As a women age increases, so too does the risk for
chromosome aneuploidy in the foetus.
 50% chromosomally abnormal foetuses are trisomic, with
trisomy 16 being the most frequent.

6.  Aneuploid is the result of meiotic non-disjunction, where the
failure of homologous chromosomes to separate during
anaphase results in one gamete containing both homologues,
the other containing the none.
 Upon fertilization, the foetus is either monosomic or trisomic.

8.  90% of non-disjunction events are of maternal origin, three
fourths arising in anaphase Ⅰ.
 10% occur due to non disjunction during either meiotic division
or spermatid development.
 MULTIPLE MISCARRIAGES AND/OR FOETAL LOSS
 Causes for multiple miscarriages can be chromosomal,
anatomical, immunological or hormonal.
 Half of miscarriages due to chromosome abnormality, of these
2% have unbalanced translocations.
 If there is no addition or loss of genetic information, the
karyotype is described as ‘balanced’: the individual is
phenotypically unaffected.
 If the rearrangement cause genetic information to be lost and/or
gained, the karyotype described as ‘unbalanced’, the individual
is phenotypically affected.

9.  KNOWN OR SUSPECTED FAMILY HISTORY OF
GENETIC DISEASE OR MULTIFACTORIAL
DISORDER
 If a monogenic, polygenic or multifactorial disorder is in the
family history, the pregnancy may be affected.
 Confirmed family history, accurate diagnosis, reliable testing
are key factors in prenatal diagnosis.
 ETHNICITY AT INCREASED RISK FOR GENETIC
DISEASE
 Certain ethnic groups have an increased incidence of specific
genetic conditions due to lack of migration, genetic drift or
heterozygote within the given population or geographic area.

10.  If these inherited mutations cause disease in the homozygous
state, members of the given population are at increased risk of
having children affected with recessive conditions . E.g.: Tay
Sachs Disease
TERATOGENS
 Maternal disease (e.g. Insulin-dependent diabetes, maternal
phenylketonuria), infection(e.g. Toxoplasmosis, rubella) or
exposure to internal or external substances (e.g. Medications,
alcohol, radiation) are not associated with chromosomal or
genetic disease, but may lead to foetal abnormality, distress or
demise.
 Information required to investigate the specific teratogenic
effects of a given exposure includes:
 Type of agent.
 Timing and duration of exposure.
 Dosage.

11.  ABNORMAL ULTRASOUND FINDINGS
 This may prompt invasive prenatal diagnostic measures if
foetal structural abnormalities or markers associated with
chromosome conditions are identified.
 For example, ultrasound may suggest the presence of
chromosomal aneuploidies such as Down Syndrome, genetic
syndromes such as dwarfism, hereditary renal disorders or
isolated birth defects.
 ABNORMAL MATERNAL SERUM SCREEN RESULTS
 Maternal serum screening may identify women at increased
risk of having a child with Down Syndrome, trisomy 18 or an
open neural tube defect (spina bifida).
 In these cases, positive serum screen results often prompt
consideration of diagnostic testing by amniocentesis.

12. METHODS OF PRENATAL
DIAGNOSIS
Prenatal diagnosis employ a variety of Invasive and Non-invasive
technique to determine the health and condition of developing
foetus.
INVASIVE
METHODS
NON-INVASIVE
METHODS
AMNIOCENTESIS ULTRASONOGRAPHY
CHORIONIC VILLUS
SAMPLING
MAGNETIC RESONANCE
IMAGING
BIOPSY FROM FOETAL
TISSUE
CELL FREE-FOETAL
DNA
CORDOCENTESIS TRIPLE TEST

13. AMNIOCENTESIS
 Discovered by Dr. Povl Riis-University of Copenhagen(1955).
 Invasive procedure performed at 15-18 weeks of gestation.
 Procedure for obtaining a sample of amniotic fluid from a pregnant
women.
 Amniotic fluid contains exfoliated foetal cells that may be cultured
to reveal foetal karyotype, and/or perform biochemical testing and
molecular analysis.
 Because of removal of amniotic fluid along with suspended foetal
cells, the levels of alpha-feto protein (AFP-10-150ng/mL) are
commonly measured to screen for neural tube and abdominal wall
defects. Normal range of AFP range from 0-40ng/mL .
 Elevated levels of AFP if identified, additional screening by foetal
ultrasound and for the presence of acetyl cholinesterase (AChE) in
amniotic fluid may clarify whether an open neural tube or ventral
wall defect is present.

14.  3rd trimester of pregnancy, the amniotic fluid can be analyzed
for determination of foetal lung maturity.
 This is important when the foetus is below 35 to 36 weeks of
gestation, because the lungs may not be mature enough to
sustain life.
 This is because the lungs are not producing enough surfactant.
 So after birth, the infant will develop respiratory distress
syndrome.

15. PROCEDURE
 Out patient procedure either with a use of local anaesthetic or
without it.
 First, ultrasonography is used to locate the position of foetus in
the uterus.
 A long sterile needle is inserted through the abdominal wall
into the amniotic sac.
 About 30-40 mL amniotic fluid are withdrawn to the needle.
 From that 2-3 mL of fluid is taken in a 5 mL syringe and the
fluid along the syringe is discarded.
 This is done because the first mL of fluids are likely to contain
maternal blood cells, muscle cells, fibroblast etc.

16. Fig: Amniocentesis

17.  The foetal cells are separated from amniotic fluid and placed
in culture medium that stimulate it to grow genetic test
(biochemical analysis, chromosomal analysis, molecular
analysis) are then performed on the cultured cells.
 Amniocentesis is commonly used for the prenatal diagnosis of
chromosome disorder and is a easier procedure than CVS.
Complication with amniocentesis are uncommon.

18. THE USE OF AMNIOCENTESIS IS RESTRICTED TO
CERTAIN CIRCUMSTANCES:
• When the mother is over age 35. The risk of having children
with chromosome abnormalities increases dramatically after
this age. The majority of all amniocentesis procedures are
performed because of advanced maternal age.
• When the mother has already had a child with a chromosomal
aberration. The reoccurrence risk in such cases is 1-2%.
• When either parent carries one or more structurally abnormal
chromosomes. This situation may cause an abnormal number
of chromosomes in a child.
• When the couple had a number of previous miscarriages or
unexplained fertility problems.

19. POTENTIALADVANTAGES AND
DISADVANTAGES
ADVANTAGES DISADVANTAGES
•Early diagnosis. •Miscarriage while performing
•Cell culture. •Needle might hit the baby
•Source of foetal DNA. •Mother may experience side
effects (cramping, leaking of
fluid, and irritation around the
area of puncture)

20. CHORIONIC VILLUS SAMPLING
 Discovered by Giuseppe Simoni.
 Major disadvantage of amniocentesis is that the cell obtained
must be cultured before genetic test can be performed. So
takes time to obtain the test results.
 CVS collects a larger amount of foetal tissue which eliminate
the necessity of culturing the cell.
 CVS was first used for prenatal diagnosis in the 1970s and
1980s.
 Can be used to yield information on foetal chromosome status,
diagnose single gene disorders [FISH] or assay for
biochemical diseases.

21. An invasive procedure by which a sample of some of the
placental tissue is obtained.
CVS doesn't provide information on Neural Tube
Defects. So women who are undergoing CVS need to
follow blood test.
Typically performed at 10-12 weeks of pregnancy.

22. PROCEDURE
 A catheter is passed via the vagina through the cervix and into
the uterus to the developing placenta under ultrasound
guidance.
 Alternative approaches are:
 TRANSCERVICAL
 TRANSABDOMINAL
 The introduction of the catheter allows sampling of cells from
the placental chorionic villi.
 The tip of the tube placed in contact with the chorione (the
outer layer of placenta).
 Suction is then applied and a small piece of chorione is
removed.
 Chorionic tissue containing a millions of actively dividing
foetal cells that can be used directly in many genetic test.

23.  The cells can also be grown in culture for biochemical or
molecular biologic analysis.
The most common test employed on cells obtained by CVS is
chromosome analysis to determine the karyotype of the foetus.

24.  CVS has a small but significant rate of morbidity for the foetus
(loss rate-0.5-1% higher than women undergoing
amniocentesis).
 CVS can be associated with limb defects in the foetus.
 The possibility of maternal Rh sensitization is present.
 The possibility that maternal blood cells in the developing
placenta will be sampled instead of foetal cells and confound
chromosome analysis.

25. SUMMARY
 The commonest indication of prenatal diagnosis is advanced
maternal age, family history of chromosome, single gene or
structural abnormality and multiple pregnancies.
 The significance of prenatal diagnosis findings is clear.
 Invasive procedures as amniocentesis or CVS is usually
requires for diagnosis of chromosome and single gene
disorders.
 Invasive procedures convey small risk for miscarriage (0.5-1%
for amniocentesis, 2-3% for CVS).

26. REFERENCE
• Pierce Benjamin A(2013), Genetics: A Conceptual Approach,
5th edition, W.H.Freeman Publication, pp.414-425
• Phadke Shubha R(2007), Genetics for Clinicians, Prism Books
Pvt. Ltd, Bangalore, pp.346-359
• Verma P.S, Agarwal V.K(2016), Genetics, 1st edition, S. Chand
& Company Pvt. Ltd., Ram Nagar, New Delhi, pp.233-234
• http://library.med.utah.edu/WebPath/TUTORIAL/PRENATAL
.html, 11/11/2015.
• Binns Victoria, Hsu Nancy(2002), Encyclopaedia of Life
Sciences, John Wiley & Sons Ltd., http://els.net, 30/05/2001