Prenatal Testing And Screening

1. Prenatal Testing And Screening

2. Lecture Outline • Definitions • Age related risks • Etiology and phenotype of chromosome anomalies • Risks, phenotype and testing options of ONTD • 1st and 2nd Trimester Prenatal Testing Options • 1st and 2nd Trimester MS Screening Options • New approaches to combining these tools • Ultrasound as a screening tool

3. Testing Defined A procedure that (in most cases) provides a definitive answer to the question that is being asked. Tests that have low false positives and negatives are considered diagnostic. In the case of prenatal testing there is a risk of miscarriage associated with all the currently available diagnostic invasive tests.

4. Screening Defined • Identify those at increased risk who are not be perceived to be at risk • Does not dx definitively • Follow-up options available for definitive information • Sensitivity=True positives/all affected • Specificity=True negatives/all unaffected

5. Baseline Risk for Having a Child With a Serious Birth Defect 3-5%

6. WE DON’T GET BETTER WITH AGE

8. NORMAL MALE KARYOTYPE 46,XY

9. NORMAL FEMALE KARYOTYPE 46, XX

10. WHEN MEIOSIS FAILS Non-disjunction Normal Sex cell production Monosomy Sex Cells Sex Cells

11. T21 Tid Bits • ~70% T21 due to an error in maternal meiosis I • ~ 20% maternal meiosis II • ~ 5% occur during spermatogenesis (meiosis II) • 5% of trisomic 21 error in mitosis • no advanced maternal age and there is no preference for which chromosome 21 is duplicated in the mitotic error • most common chromosomal abnormalities in liveborn children

12. ~1/700

13. Phenotype • Moderate mental retardation • Characteristic facies • upslanting palpebral fissures • epicanthic folds, • midface hypoplasia, • macroglossia • Congenital malformations • heart (30-40%), atrioventricular canal • gastrointestinal tract, such as duodenal stenosis or atresia, imperforate anus, and Hirschsprung disease • Leukemia (both ALL and AML) 10-20x • acute megakaryocytic leukemia occurs 200 to 400 times more frequently in the Down syndrome • 90% have significant hearing loss, usually of the conductive type

14. Trisomy 18, Edward syndrome 1/8000

15. Facial • microcephaly with prominent occiput • narrow bifrontal diameter • short palpabral fissures • low-set malformed ears • cleft lip +/- palate • narrow palatal arch • micrognathia • Skeletal • neck • webbed • chest • short sternum • widely spaced nipples • hips: • small pelvis, congenital dislocation of the hips, limited hip abduction • extremities: • phocomelia • rockerbottom feet or equinovarus • short dorsiflexed big toes fixed flexion deformity of the fingers (overlapping of the 2nd and 5th fingers over the 3rd and 4th fingers) • simple arch pattern of the fingers and toes • hypoplasia of fingernails • single crease of 5th finger or all fingers (absence of interphalangeal flexion creases) • simian crease • Central Nervous System • severe mental retardation • hypotonia -> hypertonia • neural tube defects • poor suck and weak cry • failure to thrive • ocular anomalies • Respiratory • apnea • Cardiovascular( >95%) • major: VSD, ASD, PDA • minor: transposition, ToF, coarctation, anomalous coronary artery, dextrocardia, • aberrant subclavian artery, arteriosclerosis, PS, bicuspid aortic and/or pulmonic valves • Gastrointestinal • inguinal, umbilical, and/or diaphragmatic hernia • congenital defects: • diastasis recti, heterotopic pancreas, malrotation, Meckel's, tracheoesophageal fistula • Genitourinary • cryptorchidism • congenital defects: • double ureter, ectopic kidney, horseshoe kidney, hydronephrosis, polycystic kidney Trisomy 18

16. 47,XXY

17. severe mental retardation • coloboma, • (a cleft palate) and/or a cleft lip • hypotonia • skeletal abnormalities (polydactyly) • Renal heart defects • holoprocencephaly • T13 Patau syndrome • 1/5,000

18. 1/1000 Kleinfelter syndrome

19. 45, X

20. 45, X Miscarriage Turner syndrome1/3000 liveborns

21. Neural Tube Defects • Second most common major congenital defect (1-2/1000) • Not a chromosome anomaly • Routinely tested and screened for in pregnancy • Failure neural tube to close at 28 days gestation • 20% are closed lesions and difficult to detect prenatally

22. Open Neural Tube Defects

23. Open lesions Closed lesions

24. In 1976 the American College of Obstetrics and Gynecology recommended prenatal diagnosis be offered to all women 35 years of age and older at delivery.

25. INDICATIONS FOR PRENATAL DIAGNOSIS • Maternal age > 35 years at EDC • Abnormal maternal serum screening for: DS cut off > 1/270 Increased risk Trisomy 18 or 13 Smith-Lemli-Opitz syndrome ONTD • Previous child with chromosomal abnormality or diagnosable genetic disorder • Balanced translocation carrier • Ultrasound anomaly (soft sign vs frank anomaly)

26. PRENATAL DIAGNOSTIC PROCEDURES • AMNIOCENTESIS • CHORIONIC VILLUS SAMPLING • PERCUTANEOUS UMBILICAL CORD SAMPLING

27. AMNIOCENTESIS PERFORMED ROUTINELY 16-20 WEEKS

28. ULTRASOUND GUIDED AMNIOCENTESIS

29. Amniocentesis Testing • Chromosome analysis • AF-AFP levels • Acetylcholinesterase • Risk of miscarriage associated with procedure 1/100-1/400 ONTD

30. Advantages • Highly reliable results 99+% • Familiar • Long standing reputation • NTD detection

31. Disadvantages • Late in gestation • Decision making • Privacy • Mom feels movement • Fear of needles • Needle invades the sac

32. Fetus: 12 weeks gestation

33. Chorionic Villus Sampling Transcervical Performed >10 wks-13 weeks Chromosome analysis Risk 1/100-1/200 Transabdominal

34. trophoblastic shell cells • Syncitiotrophoblasts – poly-proliferate tissue type=directs • cytotrophoblasts • Mesodermal core=tissue culture • frorm finger-like extensions

35. Disadvantages • Placental mosaicism 1% of CVS is confirmed in the fetus ~ 10-40% • Second trimester amniocentesis mosaicism ~ 0.1-0.3% & confirmed in a fetus up to 70% of the time. • ?LRD risk prior to 70 days gestation (10 weeks) • Higher loss rate • Less access to procedure • Higher chance of insufficient sample • Early test=risk of sampling a fetus potentially destined to miscarry • No ONTD testing • More risk of vaginal bleeding • Speculum

36. Benefits • Earlier in gestation • rapidly growing cell cultures practically free of maternal cell contamination • an efficient direct method to obtain high quality metaphases from the of the syncitiotrophoblasts tissue which the fetal karyotype is defined within a few hours of chorionic villi sampling (specialty cyto techinque) • is suitable for a rapid, direct diagnosis of the related metabolic diseases. • placental mosaicism (trisomic rescue in fetus) can increase the risks of genetic abnormalities such as uniparental disomy G. Simoni1, Human Genetics 1983  

37. Fetal Blood Sampling “PUBS”

39. Percutaneous Umbilical Cord Sampling(PUBS)or Cordocentesis • ~2% risk of loss • Technically difficult prior to 20 weeks • Blood disorders such as hemophilia and anemia • Useful for detection of Rh isoimmunization of the fetus (blood cell count and oxygen level)→erythroblastosis fetalis (HDN) • Chromosomal abnormalities Fetal karyotype in 48 hours • Infections such as toxoplasmosis and rubella. • The procedure is also used to perform blood transfusions to the fetus and to administer medication directly into the fetal blood supply.

40. Reproductive Decision Making RISK Fetal Aneuploidy Procedure Related RISK

41. TO TEST OR NOT TO TEST • I want to know • The benefits outweigh the risks • Options are desirable • Because my doctor says so….. • Not sure I want to know • Risks are a big worry • Options stink • Because my doctor says so…. So what to do what to do…………..

42. SECOND TRIMESTER MATERNAL ANALYTES FOR ANEUPLOID SCREENING FETAL Alpha-fetoprotein- AFP Estriol- uE3 PLACENTAL Estriol- uE3 Human chorionic gonadotrophin- hCG Inhibin-A

43. 2nd Trimester MSS Overview Used for detection of: • ONTD • Down syndrome • trisomy 18 • Smith-Lemli-Opitz syndrome

44. XMoM 0.7 2.1* 0.7 2.1 Second trimester MSS ONTD DS T18 SLO • AFP • HCG • uE3 • Inhibin-A 0.65 0.36 0.4* Serum Marker 0.21*

45. Smith Lemli Opitz Syndrome • Defect enzyme in the conversion of 7-dehydrocholesterol to cholesterol. • Affects 1 in 20,000 to 40,000 births • Autosomal Recessive • Mental Retardation • Slow growth • Heart defects • Facial cleft • Screen positive women have uE3 < 0.4 MoM • ~2% baby affected • Testing AF for 7-8- dehydrocholesterol (7/8-DHC) levels

46. Other…….. Turner T13 Triploidy Pregnancy complications • AFP • HCG • uE3 • Inhibin-A Serum Marker

47. uE3 lower than 0.1 MoM • Increase risk for x-linked ichthyosis

48. ONTD screening • Abnormal Screen MS-AFP > 2.5 MoM • Elevated MSAFP recommendations: • Ultrasound • 90% r/o spinal lesions 100% r/o anencephaly • VWD reduced with normal scan • If MSAFP >4.0 MoM and NL U/S offer invasive testing

49. Detection Rates MSAFP Add Ultrasound • Anencephaly 100% 100% • Spina Bifida 85-90% 90% • VWD • Omphalocele 70% 95% • Gastroschisis 90% 95%

50. Screening for DS 2nd Trimester 1/270 Cut-off DR% FPR% • Age 20 5 • Age AFP 30 5 • Age AFP + HCG 55 5 (Double) • Age AFP+uE3+HCG 61 7 (Triple) • Age AFP+uE3+HCG+Inhibin-A 75 5 (Quad)