prenatal diagnosis

1. SANIL VARGHESE PRENATAL DIAGNOSIS

2. PRENATAL DIAGNOSIS CORDOCENTESIS FETOSCOPY TRIPLE TEST PRE-IMPLANTATION GENETIC DIAGNOSIS POLAR BODY BIOPSY BLASTOMERE BIOPSY KARYOTYPING GENE MAPPING

3. CORDOCENTESIS Cordocentesis , 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.

4. PROCEDURE An 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.

5. CORDOCENTESIS

6. 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 .

7. COMPLICATION Blood loss from the puncture site Infection Drop in fetal heart rate Premature rupture of membranes Fever Chills Leaking of amniotic fluid

8. FETOSCOPY Fetoscopy 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

9. 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.

10. FETOSCOPY

11. PURPOSE Evaluate 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.

12. 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.

13. 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 )“.

14. 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.

15. INCREASED RISK OF MSAFP UE3 hCG DOWN’S SYNDROME ↓ ↓ ↑ TRISOMY 18 ↓ ↓ ↓ NTD’s ↑ NORMAL NORMAL MOLAR PREGNANCY ↓ ↓ ++↑ MULTIPLE GESTATION ↑ NORMAL ↑ TRIPLE TEST

16. 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).

17. ADVANTAGES Helps prevents birth of children with chromosomal anomalies and single gene disorders. Eugenics.

18. 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.

19. 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).

20. 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.

21. The genetic input of both parents can be studied. ADVANTAGE

22. Karyotyping It is the procedure by which the chromosomes are arranged based on the sizes, position of the centromere & pattern of the chromosome binding

23. 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.

24. 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 .

25. GENE MAPPING Gene mapping, also called genome mapping, is the creation of a genetic map assigning DNA fragments to chromosomes.

26. TYPES Genetic mapping :- The relative position between 2 genes of a chromosome are determined using linkage analysis. Physical mapping :- Using techniques like FISH technique, it is possible to determine the absolute position of a gene on a chromosome.

27. 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.

28. 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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