Karyotyping of the fetus can be done through all of the following invasive methods except:
Ans. d. Fetal skin biopsy (Ref: Williams 23/ep299-30I; Dutta 6/e pit)?. 108, 642>"Currently there are three routine itw.! of obtaining fetal tissue: Amniocentesis at 15 to 20 weeks, gestation, chorionic villus sampling at 10 to 12 weeks, a tut percutaneous umbilical blood sampling (cordocentesis) past 18 weeks. In addition, experimental invasive feta! sampling methods such as early amniocentesis, late transabdominal chorionic villus sampling, skin biopsy, liver biopsy, and muscle biopsy arc being used. Although amniocentesis and chorionic villus sampling are hath widely accepted and relatively safe, they are both invasive and carry a definite, albeit small\ procedure-related risk. Because of this risk and the cost of testing, only women older than 35 who have a greater risk for fetal aneuploidy are currently offered prenatal testing. "A G3P2, pregnant comes to your clinic at 18 weeks of gestation for genetic counselling. She has a history of two kids born with thalassemia major. The recommended test for this patient is Cordocentesis, since this patient is presenting at 18 weeks, a quick method to diagnose thalassemia antenatally is needed as the legal age of abortion is only till 20 weeks. Fetal karyotyping takes 7--10 days when done through CVS or amniocentesis as the shredded cells are to be cultured. Cordocentesis is a much quicker method to achieve the same."Fetal blood karyotyping can be accomplished within 24 to 48 hours. Thus, it is significantly quicker than the 7- to 10-day turnaround time with amniocentesis or CVS."-- Williams Obstetrics 24/e p300Cordocentesis (Percutaneous Umbilical Blood Sampling/PUBS)Cordocentesis was initially described for fetal transfusion of red blood ceils in the setting of anemia from alloimmunization.Indications of CordocentesisFetal anemia assessmentQAssessment & treatment of platelet alloimmunizationQFetal karyotype determination in cases of mosaicism identified following amniocentesis or CVSQ.Fetal blood karyotyping can be accomplished within 24 to 48 hours. Thus, it is significantly quicker than the 7- to10-day turnaround time with amniocentesis or CVSQ.Complications of Cordocentesis* Fetal-maternal bleedingQ (40%)* Cord vessel bleeding (20 to 30%)* Fetal bradycardia (5-10%)* Procedure-related fetal loss (1.4%)AmniocentesisDeliberate puncture of the fluid sac per abdomenMC performed invasive test for prenatal diagnosis of genetic diseaseQCommonest indication is maternal ageQPerformed at 14-20 weeks, (14-16 weeks is mentioned in Dutta)QTwo samples of around 30 mlQ is takenPregnancy loss is high in early amniocentesisQIndications of AmniocentesisDiagnosticTherapeutic* Early months (12-14 weeks)Q: antenatal diagnosis of chromosomal and genetic disorders* Later months (16-18 months)Q: Fetal maturity, degree of fetal hemolysis in Rh sensitized mother, meconium staining of liquor, amniography or fetography* First half: induction of abortion by instillation of chemicals, repeated decompression in acute hy- dramnios* Second half: Decompression in unresponsive cases of chrome hydramnios, to give intrauterine fetal transfusion, amnioinfusionChorionic Villus SamplingPerformed for prenatal diagnosis of genetic disordersQTranscervical between 10-12 weeksQ & transabdominal from 10 weeks to termQA few villi are collected from chorionic frondosumQ under ultrasonic guidance with the help of a long malleable polyethylene catheter introduced transcervically along the extraovular space.Chorionic Vilius SamplingAdvantagesDisadvantages* Early diagnosis, early termination, lesser complicationsQ (as compared to amniocentesis)* Villi are good source of DNA* Increased pregnancy lossQ (as compared to amniocentesis)* Severe limb reduction defect (Oro-mandibutar limb deformity, when CVS is performed before 9 weeks)QNTD cannot be detected by CVSQ.Transabdominal CVS can be performed in 2nd and 3rd trimesterQ.Techniques for Prenatal DiagnosisFetal tissuesTechniqueTiming (weeks)Studies done on TissueRiskAmniotic fluid* Conventional Amniocentesis* Early amniocentesis15-1611-14AFP/ACHE/hCGAbortion, needle puncture injuries, placental abruption, chorio amniocentesis abruption, preterm labourAmniocytes* Conventional Amniocentesis* Early amniocentesis15-1611-14Cell culture for karyotypes, enzyme assay, DNA studies, FISH-Chorionic Villi* Transvaginal* Transabdominal8-1112-24Biochemical chromosomal. DNA2% fetal loss, limb defects, mosaicism and maternal bleedingFetal blood* Fetoscopic aspiration* Cordocentesis18-2016-20Coagulation factor Immunoglobulin antibodies estimation;DNA and enzyme study; karyotype, FSH1% fetal loss, Rhesus sensitization, fetal infection, PROMFetal liver* Fetoscopic biopsy* Percutaneous biopsy18-20Enzyme assay as in OTC deficiency-Fetal skin* Fetoscopic biopsy* Percutaneous biopsy18-20Histopathology-Fetal muscle* Fetoscopic biopsy* Percutaneous biopsy18-20Histopathology-Maternal serum* Maternal blood12-14AFP/UE3 hCGNilFetal cells in maternal circulation* Flow cytometry, PCR1 monoclonal antibodies1st trimesterFish fetal sexing DNA testesNilPre-implantation embryo biopsy* IVF Biopsy of blastocysts4-8 cell stage blastocystDNA. PCR enzymeassay-
Chorionic villus sampling
Cordocentesis
Amniocentesis
Fetal skin biopsy
Antenatal Screening