1. Prenatal Screening for Genetic Conditions
The tried-and-true
and the Pretty new
Kathy Morris, MSSW, LCGC
Senior Genetic Counselor
UNM Dept OB/GYN

2. Learning Objectives
Name 4 available prenatal screening tests for Down syndrome and Trisomy 18
Be able to state at what gestational ages each of these tests are performed
Name three differences between standard biochemical screening and non-invasive aneuploidy screening
Be able to order all these screening tests in Power Chart

3. Why screen?
Most babies with birth defects and genetic conditions are born to parents with NO RISK FACTORS
Prenatal screening: historically designed for a LOW RISK population

4. Goals of Prenatal Screening
Identify fetal abnormalities that would otherwise have been missed
Identify “high risk” patients who should be offered more testing
High detection rate with relatively low false positive rate

5. Prenatal Screening
Can be used in a “known risk” population to adjust risk estimates and help patients decide about further testing

6. Case 1 Maria
Maria is a G2P1 30 year old patient who comes to initiate prenatal care at 9 weeks’ gestation. You want to offer her prenatal screening. What is it important to tell Maria about prenatal screening so she can make an informed decision?
What do you want to ask Maria to help her make an informed decision about screening?

7. Pre-test counseling
Anyone can have a baby with a birth defect, regardless of age, exposures or family history
Review disorders being tested for-this screen does not test for everything
Screening tests do not tell for sure if fetus is affected
Positive result does not mean baby is affected, only that more testing should be considered
Negative result does not guarantee that baby is unaffected

8. Pre-test counseling Non-invasive, no risk to baby
Other (invasive) tests available to tell for sure if baby has certain conditions
Screening is optional- Make sure that patient wants testing
Make sure she’s having the type of test she wants (screening vs. diagnostic)
Genetic counseling available for patients who require more information, recommended for those who have known risk factors

9. UNM Screening Options
“Standard” Screening: Maternal biochemistry, with or without US
Ultrasound: NT and Anatomy
Non-invasive aneuploidy screening (NIPS/NIPT)
Should be offered to all patients with known risk for aneuploidy as alternative to standard screen

10. Standard Screening: Varied protocols exist
1st trimester screen-biochemistry only
1st trimester screen-biochemistry and nuchal translucency
1st trimester screen- biochemistry, NT, nasal bone
2nd trimester serum (multiple marker screen)
Combined screen:
Stepwise Sequential
Integrated
Serum integrated
Contingent
Combined screens have the highest sensitivity with lowest initial positive rate

11. Maria Part 2
Maria says she would like prenatal screening. How would you decide which test to order?

12. UNM Protocol: Stepwise Sequential Screen

13. Current UNM Protocol: Stepwise Sequential Screen
First trimester ultrasound (Nuchal Translucency)
Biochemistry (PAPP-A and hCG): 11 1/2-13 6/7 weeks
Risk numbers calculated
If not abnormal, second serum is drawn
Revised DS and T-18 risk numbers after 2nd serum

14. Sequential Screen Final report gives risk estimates for Down syndrome
Trisomy 18
Open neural tube defects (AFP, 2nd serum only)
Most effective with singleton pregnancies

15. Sequential Screen: Risk cutoffs
FOR DS AND T-18, RISK NUMBER, not MoM values, determine positive result
1st trimester nd trimester
Down syndrome /50 risk /270 risk
Trisomy /100 risk /100 risk
Open NTD > 2.5 MoM

16. Sequential Screen Detection rates After Part I After Part II
Down syndrome 77% %
Trisomy % %
Open NTD %
Initial positive rate 3% after 1st tri

17. Sequential screen in twins
Lower detection rate
Down syndrome: 65% (1st) and 79% (2nd)
Open NTD: %
Cannot interpret for trisomy 18
Diagnostic testing possible, but what to do if one twin is affected and the other is not?

18. Biochemistry 1st trimester (11 3/7-13 6/7)
PAPP-A
hCG
2nd Trimester (15 0/7-24 6/7 at ARUP)
MSAFP
Unconjugated estriol (uE3)
Inhibin A

19. Nuchal Translucency
Nuchal translucency

20. Increased NT-A non-specific risk factor
Other chromosome abnormalities (Turner, triploidy)
Heart defect
Noonan Syndrome
Skeletal dysplasias
Diaphragmatic hernia
Chest mass
Many other birth defects and genetic syndromes

21. The bigger the NT, the higher the risk of a poor outcome
Chrom.
Abnorm.
Fetal death
Major anomalies
Alive & well
< 95%
0.2 %
1.3 %
1.6%
97 %
95-99%
3.7 %
2.5%
93 % mm
21.1 %
2.7 %
10.0 %
70 %
33.3 %
3.4 %
18.5 %
50 %
50.5 %
10.1 %
24.2 %
30 %
> 6.5 mm
64.5 %
19.0 %
46.2 %
15 %
Souka, et al, 2005, n=96, 127 singletons

22. Maria Part 3
You decide, since it is the standard procedure at UNM , that you will order a stepwise sequential screen for Maria. How do you go about ordering it?

23. Sequential Screen Process
OB provider responsible for pre-test counseling
To order:
Power Chart
Ad hoc
Women’s Imaging-OB
“First trimester, NT when appropriate”
Not necessary to order genetic counseling unless a risk factor or concern
Ultrasound clinic orders FIRST serum screen
US clinic schedules 20 week anatomy scan

24. Sequential Screen Process
STARTING JANUARY: Screen ordered by ultrasound clinic in name of referring provider
Results come to ordering provider in Power Chart inbox
If abnormal, YOU contact patient, review results, refer to genetics, discuss follow-up testing options
If not abnormal, referring provider orders second sequential screen

25. What you see in Power Chart

26. “AFP4 maternal screen”

27. EER 1st trimester

28. Maria Part 4
You contact Maria about her screen results and tell her “so far so good.” You go into Power Chart to order Maria’s second screen. You type in the word “second” and you see two choices: Second sequential screen and Second integrated screen. You also know that the second part of the sequential is a quad marker screen which you can order as AFP MM 4 or AFP MS 4. Which of these orders do you place for Maria?

29. Sequential Screen Process- 2nd serum
Order “Second sequential Screen”
DO NOT order a quad screen/AFP MM4
DO NOT order a second integrated screen
Results come to ordering provider

30. Sequential Screen process
Results come to ordering provider
If abnormal, YOU contact patient to discuss
Refer to genetics to discuss follow-up testing options

31. Sequential Screen: Follow-up options
Positive 1st trimester screen
CVS may be possible
Amniocentesis
Non-invasive aneuploidy screening
Second trimester anatomy ultrasound

36. Sequential Screen: Follow-up options
Positive 2nd trimester screen for DS or T-18
Amniocentesis
Non-invasive aneuploidy screening
Second trimester anatomy ultrasound

37. Positive Sequential for NTD: 2nd Trimester
Elevated MSAFP-differential diagnosis NTD Ventral wall defect Rare congenital nephrosis Risk of obstetric complications

38. Maria Part 5
Maria’s second sequential screen shows an elevated MSAFP of MoM. What follow-up tests would you offer to find out the explanation?

39. Follow-up positive screen for NTD
Amniocentesis for amniotic fluid AFP
Anatomy ultrasound
Skull, intracranial anatomy
Spine views
Lower extremities: club feet
Abdominal wall

40. Second Trimester Multiple Marker Screen

41. Case 2, Brittany
Brittany is a 28 year old G2P1 who presents for prenatal care at 17 weeks gestation. After your thorough discussion of screening, she says she would like to screen for birth defects and genetic conditions. What test do you order?
How do you order the test in Power Chart?

42. 2nd Trimester Multiple Marker Screen
If patient is too far along for 1st trimester screen
Multiple marker screen can be done between /7 weeks
Ordered by primary OB provider who does pre-test counseling
Requires patient history form
Run by Tricore

43. 2nd Trimester Multiple Marker Screen
Triple: MSS 3
MSAFP
hCG
uE3
Quad: Order as AFPMS4 of AFPMM4
Inhibin-A

44. 2nd trimester multiple marker screen
DS detection % with triple
70-80% with quad
Trisomy 18 detection- 65% with triple or quad
NTD detection: 80-85%
5% screen positive rate-most are false positive

45. Multiple marker screen
DO NOT REPEAT if positive for chromosome abnormality
Possibility of having false negative repeat screen
Only redraw if dating error shows too early

46. Negative Quad Screen

48. What you see in Power Chart

49. Brittany, Part 2 Brittany’s quad screen report is faxed to you.
See next slide

51. Brittany, Part 3
What do you say to Brittany to explain her test results?
What follow-up testing should Brittany be offered?
What do you do to facilitate a more in-depth discussion of Brittany’s test results and of follow-up testing options?

52. Standard Screening-Advantages
Most fetuses with these abnormalities would not be identified based on family history or maternal age risk factors
Non-invasive-no risk to fetus
Less costly than diagnostic testing, NIPT/NIPS

53. Standard Screening-Disadvantages
False positive results lead to patient anxiety
High positive rate in AMA patients
Not definitive: follow-up testing needed

54. Ultrasound

55. A completely separate lecture, but…
Diagnostic test for structural malformations
Anatomy scan: 50% sensitivity for Down syndrome
90% sensitivity for trisomy 13 and 18
Will not identify sex chromosome aneuploidy

56. Non-Invasive Aneuploidy Screening (NIPS)

57. Non-invasive aneuploidy screening (NIPS)
aka Cell-free fetal DNA screening
Clinically available since 2011
DNA-based screening

58. NIPS
Cell-free DNA fragments in maternal serum analyzed, mostly trophoblastic in origin
Lab does not separate maternal from fetal DNA
Can be done after 9 or 10 weeks’ gestation
NOT a karyotype or microarray

60. NIPS Identifies more conditions than standard screening
Higher detection rate than standard screening
Endorsed by several professional organizations for use in patients with known risk factors for aneuploidy

61. NIPS Risk factors for aneuploidy Advanced maternal age (35 at EDD)
Positive standard screen
Malformation or soft markers on US
Previously affected child or pregnancy
Parental translocation carrier

62. NIPS Sensitivity: 99% for Down syndrome 97% for Trisomy 18
~90% for sex chromosome abnormalities
Specificity:
99% for all

63. NIPS Menu of tests has expanded Triploidy Several microdeletions
Trisomy 9, 16 and 22
Whole genome NIPS
Expensive-insurance usually covers when known risk factor
Genetic counseling recommended before testing

64. NIPS Positive Predictive Value: Better than standard screening
Depends upon sensitivity and prevalence

65. NIPS- Performance compared to standard screening
15,841 patients underwent standard screen and NIPS
Mean maternal age 30.7 years
DS Detection
False +
PPV
NIPT
100% (38/38)
0.06%
80.9%
Standard
78.9% (30/38)
5.4%
3.4%
Norton, et al, NEJM 2015

66. NIPS- Performance compared to standard screening
1914 woman underwent standard screening and NIPS (mean age 29.6 years)
Trisomy 21
NIPT
Standard
Sensitivity
N=5
100
False +
0.3%
3.6%
PPV
45.5%
4.2%
Trisomy 18
N=2
0.2%
0.6%
40%
8.3%
Bianchi, et al, NEJM, Feb, 2014 (Vol 370, #9, )

67. NIPS-Sources of error Placental mosaicism “Vanishing twin”
Maternal aneuploidy/mosaicism (e.g sex chromosome)
Maternal neoplasm

68. NIPS limitations Will not detect many chromosome abnormalities
Limited data about performance in multiple gestations
Limited data about detection of microdeletions
Low fetal fraction: indeterminate or “no call” result
Some data to suggest an increased risk of aneuploidy in this population

69. NIPS
Insurance companies may or may not cover, or may not cover completely
Prior authorization usually required
Cost effectiveness in the low-risk population is not documented

70. Ordering NIPS
MFM recommends NT ultrasound in conjunction if pt in 1st trimester
If NT is increased, patient may opt for diagnostic test
Increased NT may be an indicator of a structural malformation not associated with a chromosome abnormality
Ad hoc order for genetic counseling and NT ultrasound (or for genetics if patient is >14 weeks)

71. Review questions
Which of the following screening tests has the highest sensitivity for Down syndrome?
A. Quad marker screen
B. Anatomy ultrasound
C. Non-invasive aneuploidy screening
D. Stepwise sequential screen

72. Review Questions
Which of the following screening tests would be most likely to likely detect trisomy 13?
A. Non-invasive aneuploidy screening
B. Stepwise sequential screen
C. Quad marker screen
D. Triple marker screen

73. Review questions
For which condition would the positive predictive value be highest with non-invasive aneuploidy screening?
A. Trisomy 13
B. Trisomy 18
C. Trisomy 21
D. Monosomy X (Turner syndrome)

74. Review Questions
In which trimester of pregnancy can each of the following screening tests be performed?
A. First sequential screen
B. Second sequential screen
C. Quad marker screen
D. Anatomy ultrasound
E. Non-invasive aneuploidy screening
1st, 2nd, 3rd

75. Review questions
NIPS result is positive for Down syndrome. In which situation is the baby most likely to really have Down syndrome?
A. A 25 year old with negative family history, normal anatomy ultrasound.
B. A 40 year old with fetal AV canal on ultrasound
C. A 33 year old with positive quad screen, 1 in risk for Down syndrome

76. ACOG Committee Opinion, Sept. 2015
“…conventional screening methods remain the most appropriate choice for first-line screening for most women in the general obstetric population.”
“Although any patient may choose cell-free DNA analysis as a screening strategy for common aneuploidies regardless of her risk status, the patient choosing this testing should understand the limitations and benefits of this screening paradigm…”

77. ACOG Committee Opinion
“…a diagnostic test should be recommend for a patient who has a positive cell-free DNA test result.”
“Management decisions, including termination of pregnancy, should not be based on the results of the cell-free DNA screening alone.”
Women whose results are not reported, indeterminate, etc…should receive further genetic counseling and should be offered comprehensive ultrasound…and diagnostic testing…”

78. ACOG Committee Opinion
“If a structural abnormality is identified by ultrasound, diagnostic testing should be offered rather than cell-free DNA screening.”
“Cell-free DNA screening is not recommended for women with multiple gestations”
“Routine cell-free DNA screening for microdeletion syndromes should not be performed.”

79. Questions?