Prenatal Screening and Diagnosis

What is Prenatal Diagnosis?  In-utero detection of fetal anomalies General population risk is 3-5% for any birth defect  every pregnancy has a risk of carrying an abnormal fetus Risk of aneuploidy increases with maternal age  Options: Maternal age First trimester screening Second trimester serum screen Detailed ultrasound Amniocentesis Chorionic villus sampling (CVS) Non invasive prenatal test (NIPT)

Aims of Prenatal Screening and Diagnosis  Reassurance by reducing likelihood of fetal anomaly  Prepare parents/family/obstetrician/pediatrician for birth of abnormal child if pregnancy continuing  Enable rational perinatal management Further investigations and consultations, time of delivery, mode of delivery, location of delivery

Aims of Prenatal Screening and Diagnosis  Enable couples at risk of genetic disorders to have unaffected children  Identify potentially important intrauterine treatment if available  Provide information about pregnancy options available if anomaly diagnosed

Counseling for Prenatal Diagnosis  Baseline risk estimate of affected fetus  Nature and consequences of affected child  Outline options for prenatal diagnosis Risks and limitations of each diagnostic and screening technique offered Diagnostic accuracy (sensitivity, specificity, PPV, NPV) Time it takes for results Possible need for repeat procedure if failed attempt/result  Pregnancy options if affected

Counseling for Prenatal Diagnosis  Non-directive, non-judgemental  Integral part of any screening procedure  Provide adequate information  Results of tests must be passed to couple in a timely and sympathetic fashion  Set protocols for managing positive screen results

Performance of a Screening Test Test positiveTest negative AffectedTrue positiveFalse negative UnaffectedFalse positiveTrue negative  Sensitivity proportion of patients with a disease that have a positive test  False positive rate proportion of unaffected individuals yielding a positive result  Specificity Proportion of patients disease free that have a negative test

Options for Prenatal Screening and Diagnosis 1. Maternal age 2. First trimester screening 3. Second trimester serum screen 4. Detailed ultrasound 5. Amniocentesis 6. Chorionic villus sampling (CVS)

Maternal Age  Developed in the 1960s  Prevalence of aneuploidy increases with advancing maternal age  Risk of miscarriage from amnio equivalent to risk of any chromosomal abnormality at 35 or older.  Maternal age alone for prenatal diagnosis is inferior to newer screening approaches. High false + rate (whatever % are ≥ 35 in your population) Detects only 30% of infants with T21

SOGC Clinical Practice Guideline No. 187, February 2007 “The practice of using solely the previous cut-off of maternal age of 35 or over at the EDD to identify at-risk pregnancies should be abandoned”

SOGC Clinical Practice Guideline No. 187, February 2007 “All pregnant women, regardless of age, should be offered a prenatal screening test for the most common clinically significant fetal aneuploidies in addition to a second trimester ultrasound for dating, growth and anomalies”

Options for Prenatal Screening and Diagnosis 1. Maternal age 2. First trimester screening 3. Second trimester serum screen 4. Detailed ultrasound 5. Amniocentesis 6. Chorionic villus sampling (CVS)

First Trimester Screening  Needs to be done in context of prenatal program  Nuchal translucency  – weeks gestational age  Biochemical markers  PAPP-A  Free β-hCG  – weeks gestational age Not universally available  May detect impending miscarriage, cardiac anomalies

Nuchal Translucency Normal Increased

Options for Prenatal Screening and Diagnosis 1. Maternal age 2. First trimester screening 3. Second trimester serum screen 4. Detailed ultrasound 5. Amniocentesis 6. Chorionic villus sampling (CVS)

Second Trimester Serum Screen  weeks gestation  4 biochemical markers in maternal blood AFP total hCG µE3 dimeric inhibin A  Influenced by gestational age, race, diabetes, number of fetuses, maternal weight

Second Trimester Serum Screen  Expected results AFPµE3ßhCG T21  T18  NTD  If risk > predetermined cutoff then invasive testing is offered

Screening Options Confusing Nomenclature Simplified 1. NT Self explainatory 2. First Trimester Screen NT PAPP-A, free β-hCG 3. Triple Marker Screen (TMS/MSS) AFP, uE3, total hCG 4. Quad Screen TMS + dimeric inhibin A

Screening Options Confusing Nomenclature Simplified 5. Serum Integrated Prenatal Screen (SIPS/IPSS) First trimester serum screen Either TMS or Quad Screen 6. Integrated Prenatal Screen (IPS) SIPS + NT 7. NIPT

SOGC Clinical Practice Guideline No. 187, February 2007  Minimum standards for a screening test for all women:  2007:  75% DR  5% FPR  2008:  75% DR  3% FPR

Screening Performance SOGC Clinical Practice Guideline No. 187, February 2007 Screening Option Term risk cut-off DR (%)FPR (%) NT1 in FTS1 in TMS1 in Quad1 in Serum IPS1 in IPS (no inhibin A)1 in IPS1 in

What do we do? All women should be offered SIPS IPS for women ≥ 40  Will be ≥ 35 when enough certified NT centres

Options for Prenatal Screening and Diagnosis 1. Maternal age 2. First trimester screening 3. Second trimester serum screen 4. Detailed ultrasound 5. Amniocentesis 6. Chorionic villus sampling (CVS)

Detailed Ultrasound  Offered to all pregnant women  weeks gestation  Looking for: Growth and amniotic fluid volume Major fetal anomalies “Soft markers”  Ability to visualize anomalies depends on: Gestational age, fetal size, position, number Maternal body habitus

Detailed Ultrasound: “soft markers”  Ultrasound findings that are variants of normal but also associated with aneuploidy  Presence of soft markers increases the risk of aneuploidy but is not diagnostic  Individual markers vary in the degree of association with aneuploidy, therefore each assigned a likelihood ratio (LR)

Detailed Ultrasound: “soft markers”  Detection of multiple soft markers will increase the significance of the finding, compared to a single marker in isolation  No markers and normal scan Negative LR = 0.5

Detailed ultrasound: “soft markers” Soft MarkerLikelihood Ratio T 21T 18 Nuchal fold17- Ventriculomegaly9- Short humerus7.5- Echogenic bowel6- Short femur2.7- Echogenic cardiac focus2- CPC-7

Options for prenatal diagnosis 1. Maternal age 2. First trimester screening 3. Second trimester serum screen 4. Detailed ultrasound 5. Amniocentesis 6. Chorionic villus sampling (CVS)

SOGC Clinical Practice Guideline No. 187, February 2007 “Amniocentesis/CVS should not be provided without multiple marker screening results except for women over the age of 40”

Invasive Procedures: Amniocentesis  Procedure > 15 weeks gestation 20 cc of amniotic fluid aspirated Ultrasound guidance Cells from fetal skin, GI and respiratory epithelium  Cultured, stopped in metaphase  Chromosomes banded, paired and counted Only detect abnormal # of chromosomes not specific gene defects

Invasive Procedures: Amniocentesis  Procedure related risks Miscarriage 0.5 – 1% above baseline  baseline risk is 3% at 15 weeks Ruptured membranes  Most common complication  90% stop spontaneously 1/ 1000 times cell cultures fail to grow  2 – 3 weeks to get result

Invasive Procedures: Chorionic Villus Sampling (CVS)  Procedure w3d gestation Ultrasound guidance biopsy of chorionic villi  Mitotically active cells (cytotrophoblast) Transcervical or transabdominal 2 – 3 weeks for full result

Invasive Procedures: Chorionic Villus Sampling (CVS)  Risks % miscarriage rate More post procedure vaginal bleeding than amnio 1/2000 limb reduction defect if < 10 weeks Confined placental mosaicism 1%  Often follow-up with amnio if suspect CPM  Does not diagnose NTD Still need serum AFP at weeks

Additional Invasive Procedures  Fluorescent in situ hybridization (FISH)  Fluorescent tags for trisomy 21,13,18 and sex chromosomes  Rapid test result 3 days Comparative genomic hybridization Polymerase chain reaction (PCR)  Fetal blood sampling (cordocentesis)

Now… the woman at risk of a specific genetic disorder

So… you’ve diagnosed a fetal abnormality, now what do you do?

Prenatal Diagnosis: Management Options  If an abnormality is diagnosed: <23 6 weeks gestation  Do nothing (counsel, support, provide information, consults)  In-utero therapy and management  Termination of pregnancy!!!! >24 weeks gestation  Do nothing (counsel, support, provide information, consults)  In-utero therapy and management  Termination of pregnancy only if lethal Preconception counseling in future pregnancies

Prenatal Therapy and Management  In-utero therapy: present  TTTS: laser of communicating vessels  Bladder outlet obstruction: bladder shunting  Management:  Consultations with specialists (SCN, peds surgery, peds urology, peds neurology, club-foot clinic, cleft-lip and palate clinic, social work)  Preparation of family and friends  Prenatal monitoring (e.g. growth restriction)

Prenatal Diagnosis: Conclusions  Goals  Options Maternal age First trimester screening Second trimester serum screening Detailed ultrasound Amniocentesis CVS

Prenatal Diagnosis: Conclusions  Counseling Non-directive Non-judgemental Baseline risk Consequence of affected fetus Options, limitations, alternatives for diagnosis Options for pregnancy management  Don’t forget preconception counseling for future pregnancies

Trisomy 21 (Down Syndrome)  Clinical implications of diagnosis: 30% fetal demise from 12 wk to term 1/800 live births 20% die by age 5 Structural anomalies – cardiac (35%), GI Significant mental handicap Adults develop CNS changes typical of Alzheimer’s