prenatal diagnosis

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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