Transcript Diagnostic amniocentesis AND Chorionic villus sampling INDICATION

DIAGNOSTIC
AMNIOCENTESIS
AND
CHORIONIC VILLUS
SAMPLING
INDICATION
 Previous child with a chromosome abnormality or genetic disorder
 Parent is a carrier of a balanced translocation or other structural
chromosome disorder
 Parent is a carrier of a monogenic (ie, single gene or Mendelian)
disorder
 Both parents are carriers of autosomal recessive disease
 Female parent is a carrier of a sex-linked disease
 Congenital anomaly on first trimester ultrasound examination
 Abnormal results at aneuploidy screen (eg, maternal serum
analytes with/without sonographic markers of aneuploidy, cell-free
CONTRAINDICATIONS
AND
TIMING
1. Maternal alloimmunization
CVS
2. Intra uterine device (IUD) is
in situ
3. there is a risk of vertical
transmission of maternal
infection, such as human
immunodeficiency virus
(HIV), hepatitis B and C.
4. 10 and 14 weeks of gestation
Technique
Transcervical chorionic villus sampling
Transabdominal chorionic villus sampling
Genetic evaluation
Rapid karyotyping can be achieved within 2 to 48 hours of sampling by
direct examination of cytotrophoblast (ie, direct method) since these
cells have a high mitotic index and can be examined in metaphase
Due to the risk of false positive results, long-term (one week) cultures
of mesenchymal cells should be performed concurrently as these
cells better reflect fetal, rather than the placental, genotype
DIAGNOSTIC UNCERTAINTY AND
MISDIAGNOSIS
• The false negative rate with CVS is extremely low
0.03 percent in one series of over 62,000 procedures
• In contrast, amniocentesis should be performed to rule out a false
positive test when the mosaic karyotype is found in mesenchymal
cells.
• If the chorionic villus sample is inadequate for both direct
preparations and long-term cultures, long-term culture appears to
be more reliable than a direct preparation
POST PROCEDURE CARE
• Women may resume normal physical activity after
the procedure. We generally advise them to avoid
strenuous activity and sexual intercourse for 24
hours. We also inform them that some spotting is
normal, but they should call for persistent
bleeding, pain, fever, or other concerns.
COMPLICATIONS
• Total fetal loss rate
• Perinatal loss
• Loss of multiple gestation
• Failure to obtain a sample
• Maternal cell contamination
• Limb-reduction defects and oro mandibular hypo
genesis
• Bleeding
• Infection
• Feto maternal hemorrhage
• Rupture of membranes
AMNIOCENTESIS
• Amniocentesis for prenatal genetic studies is technically possible at any gestational age after
approximately 11 weeks of gestation, but is optimally performed at 15 to 17 weeks of gestation.
• Procedures performed before 15 weeks (ie, early amniocentesis) are associated with higher fetal loss
and complication rates, including culture failure, and should be avoided
• Test results are available sooner when blood is the source of cellular material: 24 to 48 hours versus 7
to 10 days when amniocytes or chorionic villus cells are cultured.
• laboratory-related failure rates of karyotyping increase significantly with advancing gestation so that, in
the third trimester, karyotyping is more likely to fail than microarray
• Fluorescence in situ hybridizationInterphase fluorescence in situ hybridization (FISH) provides a
limited karyotype within 24 to 48 hours, but only detects aneuploidy of chromosomes 13, 18, 21, X, and
Y, which are the most common causes of aneuploidy.
Evaluation of fetal demise
Chromosomal abnormalities are more prevalent in stillborn than liveborn infants.
Amniocentesis to obtain fetal cells as soon as possible after fetal demise is more likely to yield
viable cells for analysis than tissue obtained after delivery.
Use of chromosomal microarray appears to increase diagnostic yield because it does not require
cell culture.
Fetal lung maturity
Antibiotic prophylaxis
Post-procedural care
DISCOLORED SAMPLES
Blood-tinged amniotic fluid
green or brown pigment in second trimester amniotic fluid
COMPLICATIONS AND ADVERSE
OUTCOMES —
• The major complications of amniocentesis are
• rupture of membranes,
• direct fetal injury,
• indirect fetal injury,
• infection,
• Vertical transmission
• Innoculation by bowel flora
• and fetal loss.
•
Maternal complications related to the procedure, such as amnionitis, are rare,
occurring in less than 1/1000 procedures.
Cell culture failure
Amniocytes fail to grow in culture in 0.1 percent of samples
Mosaicism
True mosaicism is defined as one or more abnormal cell lines plus a normal cell line in at least two primary cultures from
the same individual; it occurs in 0.1 to 0.2 percent of pregnancies undergoing amniocentesis
Pseudomosaicism (ie, an abnormal cell line confined to one culture flask) is more common, occurring in up to 8 percent of
pregnancies
Obstetrical complications
Third trimester amniocentesis
ANEUPLOIDY SCREENING
IN
MULTIPLE GESTATION
•
Monozygotic twins are thought to have the same
Down syndrome risk per pregnancy as maternal
age–matched singletons,
• and dizygotic twin pregnancies are thought to have
twice the risk of at least one affected fetus as maternal age–matched
singleton pregnancies.
● COMBINED
offering Down
syndrome screening with the
first-trimester combined test,
which can provide fetus-specific
risk assessment.
TEST
• We suggest
• Increased nuchal translucency at >10 and <14
weeks of gestation is a marker for Down
syndrome, other aneuploidies, congenital
malformations, and development of twin-twin
transfusion syndrome (TTTS).
• Maternal serum analyte
interpretation is
problematic in twin
pregnancies since both twins
contribute to the analyte concentration and
analyte levels may be affected by early loss of
one or more embryos of a multiple gestation
• Measurement of nuchal thickness can improve
the detection rate and help identify which
fetus is affected
the false-positive rate of nuchal translucency screening is higher
in monochorionic than in dichorionic twins because increased nuchal
translucency can be an early manifestation of TTTS as well as a marker
of aneuploidy
in vitro fertilization affects analyte values used in Down syndrome
screening and may be considered by some laboratories when calculating
screening results in twins conceived by this method
An additional factor complicating prenatal diagnosis of
monozygotic twins is that rarely these twins have different
genotypes due to fetal mosaicism or confined placental
mosaicism .
They can also be discordant for X-inactivation in females, differential
gene imprinting, and smaller-scale genetic abnormalities, such as
microdeletions
NONINVASIVE SCREENING USING
CELL FREE DNA
• Noninvasive prenatal screening for Down syndrome using cell free DNA is
challenging because the fetal cell free DNA in the maternal circulation derives from each fetus.
• Testing is commercially available for trisomies 13, 18, and 21, although less validation data are
available from twin gestations than from singletons
• An additional challenge in twin pregnancy is that the amount of cell free DNA
contributed by each twin is lower than in a singleton pregnancy and may be quite different for the two fetuses in
dizygotic twins
DIAGNOSTIC TESTING
AMNIOCENTESIS
• Most operators perform
separate
procedures on each sac for
genetic studies of multiple
gestations
• Loss rate
• The risk of amniocentesis-related loss in twin
pregnancies is likely increased by
about 1 percent above the baseline
risk of loss among twin gestations,
but the exact risk is uncertain
CVS
• Sonographic determination of chorionicity of multiple
gestations is essential prior to CVS, as chorionicity
determines the number of samples that need to be obtained.
•
If the placentas are fused and either
dichorionic or of uncertain chorionicity,
• the tip of the aspirating device should be inserted
either close to the insertion of the umbilical cord or
at the placental margin, far away from the area of
fusion, to minimize the possibility of sampling the
same fetus twice