Dr . Muhammad Rafique Assist. Prof. Paediatrics College of Medicine K K U Abha K S A. PRENATAL DIAGNOSIS. It introduces option for management. From interruption of abnormal pregnancies to prepare for specialized peri-natal care. PRENATAL Dx.------CONT. Methods of prenatal diagnosis :
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Dr . Muhammad RafiqueAssist. Prof. PaediatricsCollege of MedicineK K U Abha K S A
It introduces option for management. From interruption of abnormal pregnancies to prepare for specialized peri-natal care.
Methods of prenatal diagnosis:
.Maternal blood sampling.
.Chorionic villus sampling
Maternal trans-abdominal USG can visualize all major fetal organs at 16-18 weeks of gestation and can diagnose disorders like;
Hydrops fetalis , hydronephrosis , neural
tube defects , intestinal obstruction , CHD ,
diaphragmatic hernia , limb reduction
anomalies and growth assessment etc.
Fetal blood can be directly sampled in late gestation through USG guided per-cutaneous umbilical cord blood sampling & can detect;
.fetal anemia . Thrombocytopenia
.thalassemia. Fetal oxygenation
.acid base disorders .cells for DNA
CVS at 10-12 weeks provides good cyto- trophoblast (dividing cells) DNA for molecular analysis that can be rapidly karyotyped.
Detection possible for:
Thalassemia, hemophilia A, PKU, CAH.,
alpa-1 antitrypsin deficiency, SCD etc.
Amniotic fluid can be sampled at 10-14 weeks
gestation for fetal cells -can be cultured For
Note –complication of miscarriage <1%.
Analysis of genetic material to obtain information related to individual’s health status using either chr. analysis or DNA
2-Direct mutation analysis
It is used if
.History .pedigree construction .physical examination . diagnosis,
.counseling .follow up
Timing of counseling;
about welfare of affected individual &
is conceived ).
Some pt. need specialist care e.g . Turner synd. need endocrinologist evaluation.
Provide information about support group that provide funds for research on specific disorder
.Maternal >35 years
.Isolated birth defects
.single gene defect
.maternal high alpha fetoproteins
.sickle cell anemia
.Enzyme supplement for
.Bisphosphonate for osteogenesis imperfecta.
Replacement therapy ; e.g.
.avoiding inciting environmental factor e.g.avoid
maternal phenytoin use to avoid fetal CHD.
.By instituting treatment that reduce risk e.g.
maternal use of folic acid to avoid fetal neural-
Body cells are cultured ,arrested in mitosis in metaphase .Chromosome first evaluated microscopically then images are captured by video camera and stored on a computer . Homologous chr. are paired , arranged into Karyotype. Chromosomes are exposed to a hypotonic solution, fixed and stained with
“ trypsinGiemsa”which produces dark and light bands for detail study.
2-FISH (fluorescence in situ hybridization);
- Used to identify , presence, absence, or rearrangement of specific DNA segment.
- It involve unique DNA sequence labeled with a fluorescent dye , which is exposed to single stranded DNA on a microscopic slide.
-Probe, pairs with its complementary DNA sequence and can be visualized by fluorescence microscopy.
- It is particularly useful for detecting very
small deletion which not detectable by band
3-Spectral karyotyping (SKY) & multicolour FISH;
Re-arrangement found in tumours.
4-COMPARITIVE GENOMIC HYBRIDIZATION(CGH)
-FISH based method to measure differences in
a particular DNA sequence / chr. segment
between two different DNA samples.
-Pt’s DNA labeled with green fuorescent dye & normal reference DNA with red .
-Equal amount of two mixed &used for FISH.
4-COMPARITIVE GENOMIC HYBRIDIZATION(CGH)
-Ratio of green to red fluorescence measured along each chr.
-Region of amplification of pt’s DNA shows excess green fluorescence & region of loss of pt’s DNA shows excess of red fluorescence.
-If green and red same 1:1,chromosome would appear yellow.