prenatal diagnosis
TRANSCRIPT
SANIL VARGHESE
PRENATAL DIAGNOSIS
PRENATAL DIAGNOSIS
CORDOCENTESIS
FETOSCOPY
TRIPLE TEST
PRE-IMPLANTATION GENETIC DIAGNOSIS
POLAR BODY BIOPSY
BLASTOMERE BIOPSY
KARYOTYPING
GENE MAPPING
CORDOCENTESISCordocentesis, also sometimes called Percutaneous Umbilical Cord Blood Sampling (PUBS), is a diagnostic test that examines blood from the fetus to detect fetal abnormalities. Cordocentesis is performed after 17 weeks of pregnancy.
PROCEDUREAn advanced imaging ultrasound determines the location where the umbilical cord inserts into the placenta. The ultrasound guides a thin needle through the abdomen and uterine walls to the umbilical cord. The needle is inserted into the umbilical cord to retrieve a small sample of fetal blood.
CORDOCENTESIS
PURPOSE
To Help In Diagnosis Of:Malformations of the fetus.Fetal infection (i.e. toxoplasmosis or rubella)Fetal platelet count in the maternal circulation.Fetal anemia.Isoimmunisation.
COMPLICATION
Blood loss from the puncture siteInfectionDrop in fetal heart ratePremature rupture of membranesFever ChillsLeaking of amniotic fluid
FETOSCOPYFetoscopy is an endoscopic procedure during pregnancy to allow access to the fetus, the amniotic cavity, the umbilical cord, and the fetal side of the placenta.It is done during & after 18 weeks of pregnancy
PROCEDURE
A small (3–4 mm) incision is made in
the abdomen, and an fetoscope is
inserted through the abdominal wall
and uterus into the amniotic cavity.
Fetoscopy allows medical interventions
such as a biopsy or a laser occlusion of
abnormal blood vessels.
FETOSCOPY
PURPOSEEvaluate the fetus for birth defects, such as spina bifida as well as other defects which can only be confirmed by a Fetoscopy.To collect samples of blood from the umbilical cord, e.g. hemophilia or sickle cell anemia.Collect samples of skin tissue from the fetus. The tissue can be tested for some inherited diseases.
COMPLICATIONS
Miscarriage, as high as 12%.Excessive bleeding, infection, or excessive leakage of the amniotic fluid.Preterm rupture of the membranes.Mixing mother’s blood with baby’s blood.
TRIPLE TEST
3 tests:• Maternal Serum Alpha-fetoprotein
(MSAFP)• Unconjugated estriol• Human chorionic gonadotropin (hCG)
Also called as “Triple screen“, the “Kettering test”, the “Bart's test” or "Multiples of the Median
(MoM)“.
The triple test is an investigation performed during pregnancy in the second trimester (15-18 weeks) to classify a patient as either high-risk or low-risk for chromosomal abnormalities (and neural tube defects). The triple screen test involves drawing blood from the mother. The blood sample is then sent to the laboratory for testing. AFP is is produced in the yolk sac and fetal liver.
INCREASED RISK OF
MSAFP UE3 hCG
DOWN’S SYNDROME
↓ ↓ ↑
TRISOMY 18 ↓ ↓ ↓NTD’s ↑ NORMAL NORMAL
MOLAR PREGNANCY
↓ ↓ ++↑
MULTIPLE GESTATION
↑ NORMAL ↑
TRIPLE TEST
PRE-IMPLANTATION GENETIC DIAGNOSIS / EMBRYO SCREENING
As PGD can be performed on cells from different developmental stages, the biopsy procedures vary accordingly. Theoretically, the biopsy can be performed at all preimplantation stages, but only three have been suggested: on unfertilised and fertilised oocytes (for polar bodies, PBs), on day three cleavage-stage embryos (for blastomeres) and on blastocysts (for trophectoderm cells).
ADVANTAGES
Helps prevents birth of children with
chromosomal anomalies and single
gene disorders.
Eugenics.
POLAR BODY BIOPSY
The first and second polar body of the
oocyte are extruded at the time of the
conclusion of the meiotic division,
normally the first polar body is noted
after ovulation, and the second polar
body after fertilization.
By analyzing polar bodies it is possible to study maternal genetic makeup.The disadvantage of polar body biopsy is that, it detect paternally derived chromosomal disorders & single gene disorders (autosomal dominant disorders, autosomal recessive disorders and sex-linked disorders).
BLASTOMERE BIOPSY
It is also called Embryo biopsy, Cleavage-stage biopsy.Cleavage-stage biopsy is generally performed the morning of day three post-fertilization, when normally developing embryos reach the eight-cell stage.A hole is made in the zona pellucida and one or two blastomeres containing a nucleus are gently aspirated or extruded through the opening.
The genetic input of both parents can be studied.
ADVANTAGE
Karyotyping It is the procedure by which the chromosomes are
arranged based on the sizes, position of the centromere & pattern of the chromosome binding
• The test can be performed on a sample of blood, bone marrow, amniotic fluid, or tissue from the placenta.The sample is placed into a special dish and allowed to grow in the laboratory. Cells are later taken from the growing sample and stained. The laboratory specialist uses a microscope to examine the size, shape, and number of chromosomes in the cell sample.
The stained sample is photographed to provide a karyotype, which shows the arrangement of the chromosomes.
Certain abnormalities can be identified through the number or arrangement of the chromosomes.
Chromosomes contain thousands of genes that are stored in DNA, the basic genetic material.
GENE MAPPING
Gene mapping, also called genome
mapping, is the creation of a genetic
map assigning DNA fragments to
chromosomes.
TYPES
1. Genetic mapping:- The relative position
between 2 genes of a chromosome are
determined using linkage analysis.
2. Physical mapping:- Using techniques like FISH
technique, it is possible to determine the
absolute position of a gene on a chromosome.
Fluorescent In Situ Hybridization (FISH)
FISH is the most commonly applied method to determine the chromosomal constitution of an embryo. In contrast to karyotyping, it can be used on interphase chromosomes, so that it can be used on PBs & blastomeres.The cells are fixated on glass microscope slides and hybridized with DNA probes. Each of these probes are specific for part of a chromosome, and are labelled with a fluorochrome.
The use of probes for chromosomes X, Y, 13,
14, 15, 16, 18, 21 and 22 has the potential of
detecting 70% of the aneuploidies found in
spontaneous abortions.
In order to be able to analyse more
chromosomes on the same sample, up to
three consecutive rounds of FISH can be
carried out.
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