The document discusses methods for chromosomal evaluation during pregnancy, including both non-invasive (fetal cells from maternal blood) and invasive techniques (amniocentesis and chorionic villus sampling). It highlights the risks and complications associated with these methods, such as pregnancy loss and chromosomal abnormalities, and reviews factors influencing the outcomes of mosaicism and uniparental disomy. Additionally, it provides guidelines for prenatal diagnostics and the implications of various chromosomal findings.

1. Amniocentesis
and CVS

2. Methods of chromosomal evaluation
 Non invasive:
 Fetal cells from maternal blood
 preimplantation embryos (PGD)
 Invasive:
 amniotic fluid (amniocentesis)
 placenta (chorionic villus tissue)
 Fetal blood

3. Invasive techniques
 Amniocentesis:
 Late – second trimester after 15 weeks
 Early – earlier than 15 weeks
 Chorionic villus sampling (CVS)
 Abdominal
 Trans cervical
 Trans vaginal
 Fetal blood sampling

4. karyotype
fish
PCR

5. What can be evaluated?
 Chromosomal aberrations:
 Trisomy,
 Monosomy,
 Polyploidy,
 Marker chromosome,
 Deletion, duplication, inversion, translocation,
ring chromosome .
 Genetic aberrations (DNA)
 Infectious disease
 Biochemical markers (AFP)

6. Amniocentesis
 First introduced by Serr and Fuchs and
Riis in the 1950s for fetal sex
determination
 Only at the late 70th a static ultrasound
was used to locate the placenta and
amniotic fluid pocket
 Only In 1983, Jeanty reported a
technique of amniocentesis ’’under
ultrasound vision’’

7. Mid Trimester Amniocentesis
 Per coetaneous
 20-23g needle
 Ultrasound guided
 Usually 20cc amniotic fluid
 Results – 2 to 3 weeks

10. complications
 Pregnancy loss 0.3-1.0%.
 Increase risk:
 Needle larger than 18g
 Multiple needle insertion
 Discoloration of the fluid
 High AFP, multiple late abortions, previous
vaginal bleeding
 Placental perforation – recent studies didn’t
find correlation

11. Complications
 Leakage of amniotic fluid (better prognosis
than spontaneous leakage)
 Amnionitis
 Vaginal bleeding
 Needle puncture of the fetus
 Long term complications:
 Respiratory distress??
 Isoimmunization??

12. Amniocentesis and HIV positive
women
 Increased rate of vertical transmission
 Chemoprophylaxis previous to
amniocentesis appears to be beneficial in
preventing vertical transmission

13. Multiple Gestation
 Three methods:
 Indigo carmine injection to the first sac
 A single needle puncture sampling technique
(Jeanty 1990)
 Simultaneous visualization of two needles on
each side of the separating membrane (Bahado-
Singh 1992)
 Abortion risk – probably higher
 Detailed description of fetus
position and placental location

14. Early Amniocentesis: 9-14 weeks
 Introduced at late 80th
 10-14 weeks gestation
 Only the amniotic (inner) sac should be
aspirated
 Approximately 1 cc for gestational age
 Higher rate of pregnancy loss, talipes
equinovarus, and post procedural amniotic
fluid leakage
 laboratory failure op to 20%

15. Chorionic villus sampling
 Was developed in the 80th
 percutaneous transabdominal with 19-20g
needle

16. Chorionic villus sampling
 Was developed in the 80th
 percutaneous transabdominal
 transvaginal
 transcervical

19.  15-30mg each aspiration
 20mg ideal for cytogenetic testing
 30-40mg for cytogenetic and other direct
molecular and biochemical tests

20. CVS results
 Direct analysis examines the trophoblast
cells of the placenta (very rapidly dividing
cells)
 Results in few hours
 greater vulnerability to mitotic error
 Cultured analysis examines the
fibroblast like cells of the villus stroma or
mesenchymal core.
 Approximately 7-10 days
 Accurately reflect the chromosomes of the
fetus.

21. Risk of invasive procedure
 Early amniocentesis:
 High pregnancy loss
 High fetal malformations
 High rate of multiple needle insertions (4.7%)
 High rate laboratory failures (1.8%)
 Late amniocentesis:
 “Low” pregnancy loss (0.3-1%)
 Low rate of multiple needle insertions (1.7%)
 Low rate laboratory failures (0.2%)

22. Risk of invasive procedure - CVS
 Transabdominal CVS as safe as second
trimester amniocentesis
 Trans abdominal and transcervical CVS
are equally safe and efficacious, provided
that centers have expertise with both
approaches
 In approximately 3–5% of cases, clinical
circumstances will support one approach
over the other
 Limb reduction – not after 9 weeks

23. mosaicism
 True chromosomal mosaicism is when two
or more abnormal cells lines are detected
in two or more culture flasks from the
same individual.
 Pseudomosaicism is a term used to
describe two abnormal cell lines that are
found in only one culture flask (not
reported to the patient)

24. mosaicism
 Most often involving trisomic cell and
normal cells
 1-2% of pregnancies undergoing CVS
 0.1% of pregnancies undergoing
amniocentesis
 Clinical outcome of chromosomal
mosaicism is strongly dependent on the
specific chromosome involved and the
number of trisomic cells in both the
placenta and the fetus

25. Mosaicism (trisomic cells) in CVS
 Option of an additional prenatal diagnostic
procedure (amniocentesis or fetal blood
sampling)

26. Mosaicism (trisomic cells) in CVS
 Four possible conditions:
 Mosaicism only in the placenta not affecting
the fetus or placental function.
 Mosaicism only in the placenta not affecting
the fetus but alter placental function (IUGR)
 Trisomy cells are both in the placenta and in
the fetus
 Trisomy cells in the placenta and uniparental
disomy in the fetus

27. Mosaicism (trisomic cells) in
amniotic fluid
 Probably there are trisomic cells in the
fetus
 The true level and distribution of trisomic
cells cannot be accurately assessed with
any prenatal procedure
 Ultrasound is often the best judge of how
a baby is developing

28. Uniparental Disomy
 Arises when an individual inherits two
copies of a chromosome pair from one
parent and no copy from the other parent
 Maternal UPD – two copies from the mother
 Paternal UPD – two copies from the father

29. How does UPD happen?
 Loss of a chromosome from a trisomic
zygote, "trisomic rescue"
 Duplication of a chromosome from a
monosomic zygote, "monosomic rescue"
 Fertilization of a gamete with two copies
of a chromosome by a gamete with no
copies of the same chromosome, called
gamete complementation.

30. Trisomic rescue following an error in
meiosis
heterodisomy

31. Trisomic rescue followed an error in
meiosis II
isodisomy

32. UPD - health concerns in people
for two possible reasons:
 Parental imprinting in the case of
heterodisomy and isodisomy
 Unmasking of recessive conditions in some
cases of isodisomy

33. Clinical consequences of UPD
 molecular UPD testing should be
considered for certain chromosomes
(including 6, 7, 11, 14, 15) that are
known to have adverse phenotypic
imprinting effects.

34. Factors considered when trying to
predict the outcome of mosaicism
 the chromosome involved
 A mosaic finding 18 or 21 is likely to have
worse implications
 mosaic finding for trisomy 15 or 16 is likely to
have less implications (trisomy 15 or 16 cells
cannot survive )

35. Factors considered when trying to
predict the outcome of mosaicism
 The tissues affected and level of
trisomy in those tissues
 The tissue affected cannot be evaluated
 The level of trisomy can be only estimated

36. Factors considered when trying to
predict the outcome of mosaicism
 method of ascertainment
 CVS shows that the placenta is affected
 Amniotic fluid suggests that at least one fetal
tissue may be affected
 Fetal blood sampling confirms the diagnosis of
chromosomal mosaicism

37. Factors considered when trying to
predict the outcome of mosaicism
 ultrasound findings
 presence/absence of uniparental
disomy
 number of previous case reports
known in the literature