Maternal Serum ScreeningGP Shared Care Update October 2018

Dr Charlotte Paull

RANZCOG Advanced Trainee, Flinders Medical Centre

Why do we screen?Detection of ‘high risk’ women

Early diagnosis of fetal anomalies

Facilitate options for termination of pregnancy

Preparation for families

Fetal congenital anomalies

• Birth prevalence is 2-3% = 2.8% in SA 2010 • (doesn’t include <400g, < 20 weeks)

• Approximately half diagnosed before birth • Prenatal detection rates depend on nature, type and

frequency of abnormalities, as well as maternal factors

• 160 TOPs for fetal reasons in 2010 (1% of all births)

Gibson et al, Prenatal screening for congenital anomalies in SA , SA Birth defects register, WCHN, 2013.

Fetal congenital anomalies

• All States and Territories notify fetuses and infants with major congenital malformations to a national monitoring system

• Most common - Muculoskeletal, cardiac anomalies• Chromosomal

• T21 - 0.07% - T18 and T13 less common

• Non-chromosomal • NTDs – 0.07%• Cleft lip and palate – 0.15%• diaphragm/abdo wall – 0.07%

Gibson et al, Prenatal screening for congenital anomalies in SA , SA Birth defects register, WCHN, 2013.

Who should we screen?All women should be offered screening for chromosomal anomalies – SA PPGs

Current Practice:

81% of all pregnancies have some form of screening for T2170% first trimester

11% second trimester

South Australian GP Obstetric Shared Care Protocols. 2017

Pre-screening counsellingTest is optional

It does not give a YES/NO answer

“Low risk” does not mean “no risk”

“Increased risk” means baby “MIGHT” have a chromosomal abnormality

96% who screen “increased risk” will go on to have a normal healthy baby

First Trimester Screening

COMBINED TEST

Gold Standard

Maternal age

+

Ultrasound

+

Serum (fβhCG + PaPP-A)

SA Maternal Serum Antenatal Screening (SAMSAS) Program

Factors that can affect biochemical screening

Maternal weight50kg: 20-40% higher levels PAPP-A100kg: 20-40% lower levels PAPP-A

EthnicityAfrican: PAPP-A 50% > CaucasiansIndian: PAPP-A 10% > Caucasians

βhCG & Αfp 10% < CaucasiansChinese: PAPP-A 5% > Caucasians

Smokers:Decreases PAPP-A by 20%Decreases βhCG by 6%

IDDM:αFP decreased by 10%βhCG decreased by 5%uE3 decreased by 10%

IVF:βhCG increased by 10%PAPP-A decreased by 10%

Multiple Pregnancy:Twins – all serum marker levels doubled

- different risk levels will depend on NT

Previous affected pregnancy (T21, 18, 13)Increases the risk of recurrence by 0.75%

When to perform?

First Trimester bloods and associated complications

PAPP-A •Gestational HT•Preeclampsia•Low birth weight•Preterm birth•Fetal demise > 24/40

Free β-hCG

•Miscarriage < 24/40•Fetal demise > 24/40

< 0.3 MoM

<0.5MoM

Refer to PPGs for additional information; www.sahealth.sa.gov.au/perinatal. PAPP-A: Management of Women with a Low PAPP-A and Normal Chromosomes

Trisomy 21

Increases with maternal age

But most prevalent in young women

Screening for T21 is offered as part of routine AN screening

Counselling pre-test and timely follow up of abnormal results is a crucial part of the process

Maternal Age

Strategy Detection Rate (%) False Positive Rate

(%)

# Invasive tests to detect

1 case T21

Maternal age 55 22 200

Trimester 2

Biochemical screen

65 7 54

Trimester 1 NT alone 80 5 31

Trimester 1 NT +

biochemistry

90 4 22

Trimester 1 NT +

biochemistry + new

marker

95 3 16

NIPT 99 0.3 1.5

Theoretical population; 100,000 women and 200 trisomy 21 fetuses

Screening Strategies for Trisomy 21

SAMSAS

What is this?

What would you do with this?

NT 4.0mm

But low risk for T21 and T18

Fetal Abnormalities

Significance of individual NT measurement

NT Chromoso

mal defects

(%)

N chrom but

fetal death

(%)

Normal chrom

but major

anomaly (%)

Alive and

well (%)

<95th % 0.2 1.3 1.6 97

95-99% 3.7 1.3 2.5 93

3.5-4.4mm 21.1 2.7 10.0 70

4.5-5.4mm 33.3 3.4 18.5 50

5.5-6.4mm 50.5 10.1 24.2 30

>6.5mm 64.5 19.0 46.2 15

Nicolaides, Fetal Medicine Foundation, The 11-13 week scan

ConsiderEarly morphologyTertiary referralDetailed echoInfection screenMonitoring for resolution

What else is the test screening for?

What can we rule out? Anencephaly

Abdo wall defects

Cardiac anomalies

Skeletal defects

Megacystis

ISUOG suggested anatomical asssessment at time of 11-

13+6 week scan

Organ/anatomical area Present and/or normal

Head Present, cranial bones, falx

Neck Normal appearance, NT

Face Eyes with lens, NB, profile, lips

Spine Verebrae, intact overlying skin

Chest Symmetrical lung fields, no effusions/masses

Heart 4 symmetrical chambers, regular cardiac activity

Abdomen Stomach present in LUQ, bladder and kidneys

Abdominal wall Normal cord insertion, no umbilical defects

Extremities 4 limbs with 3 segments, hands and feet

Placenta Size and texture

Cord 3 vessel cord

How does the “anatomy screen” test perform?

In experienced hands, can identify close to 100% of targeted structures by 13 weeks

“Detection’ increases from 11 weeks

Approx 10% will need TV approach

In fetuses with normal karyotype

3% will have a structural anomaly, 1-1.5% major

40-50% will be detected at 11-13 week scan

Luchi et al, The Journal of Maternal-Fetal and Neonatal Medicine, 2012; 25(6): 675–678

Pilalis et al, The Journal of Maternal-Fetal and Neonatal Medicine, 2012; 25(9): 1814–1817

Second Trimester ScreeningSecond trimester screening for Down Syndrome – offered only if the woman presents too late for 1st Trimester screening

If a pregnancy is screened in first trimester then any request in second trimester should be confined to neural tube defect (NTD) screening only.

First trimester screening does not include a risk assessment for fetal NTDs.

14-20+6 week gestation

αFP + freeβhCG + uncong. Estriol

αFP only (for NTD only)

Second Trimester bloods and associated complications

Not

routinely

reported

AFP

• NTD

• Abdominal wall defects

• IUGR

• Abruption

• Miscarriage < 24/40

• Fetal demise > 24/40

• Preterm birth

Free β-Hcg

• Preterm birth

• Gestational HT

• Preeclampsia

• IUGR

• Fetal demise > 24/40

uE3

• Oligohydramnios

• Miscarriage < 24/40

• Fetal demise > 24/40

• IUGR** Not routinely reported.

What is ‘High Risk’?

A risk of ≥ 1:250

A Nuchal Translucency ≥ 3mm

? An increase in risk above the background risk

Refer to your tertiary centre

Antenatal Diagnostic Clinic/MFMTriaged referrals seen within 1-2 weeks

Counselled regarding risk result

Offered further testing NIPT vs Invasive Testing vs Early Morphology USS

Follow up of results

Termination of pregnancy services

Antenatal monitoring as required

Referral to other specialties – genetics, neonatology, paed surgery, social work, support groups

Invasive Testing

Chorionic Villus Sampling

10-14 weeksRisk MC 1-2%Risk of mosaicism 1%Challenging to do FISHResults in 7-10 daysNeed a full bladder

Invasive Testing cont.

Amniocentesis

15+0 onwards

Risk MC 1:200 ~ 1:900

FISH in 2 days but need to meet criteria or pay

Full results in 10-14 days

Termination of Pregnancy

If CVS abnormal – allows time for STOP

If Amniocentesis abnormal – may require medical TOP

Most obstetricians prefer to perform these at less than 14 weeks gestation Dilatation + evacuation to 16-17weeks @ FMCAdvanced gestation requires referral to PAC @ Woodville

Most women prefer surgical termination of pregnancy in these circumstances

Medical TOP involves “labour” and vaginal delivery

Non-Invasive Prenatal Testing (NIPT)What it is

Science behind it

Harmony vs NEST – numbers, how to order, cost

How should we use it

RANZCOG statement

Cell free DNA first described in 1948

Since 1997, rapid expansion of our knowledge in relation to “trafficking” of nucleic acid material between the mother and the fetus.

NIPT

What do we know?

Majority of fetal DNA present in the maternal circulation comes from the placenta (syncytiotrophoblast).

Fragments are small and released through apoptosis

Only constitute a small proportion of total cell-free nucleic acids (majority derived from maternal cells) in maternal circulation –about 3-6%

Half life is short – 15 minutes (4-30 m)

Present in useful amounts from 8-9 weeks of pregnancy

Key clinical applications

Aneuploidy ScreeningTrisomies 21/18/13Sex chromosome aneuploidy

Monosomy X, XXY, XYY etc

Rh D typing

** Sex chromosome aneuploidy screening – different to determination of fetal sex **

Gender determination – X linked disorders and congenital adrenal hyperplasia

Single gene disorders – CF, thalassaemia major, myotonic dystrophy, achondroplasia

Methods

Massive Parallel Sequencing

- simultaneous sequencing of millions of fragments of DNA at once

- aligned to a reference genome, comparing quantities of chromosomes

SNPs

Single Nucleotide Polymorphism

Targeted sequencing of particular chromosomes

Results expressed as a Z-score

Fetal Fraction

A minimal amount of free fetal DNA is required for reliable testing (>4%)

Median percent of cffDNA ~ 10%

Low fetal fraction is usually due to a relative

excess of maternal DNA in the system

Increased maternal weight reduces

the fetal fraction of cfDNA

reduced efficacy of the test.

If fetal fraction <4% redraw test

2/3rds women will have sufficient sample on

2nd drawWang et al. Prenatal Diagnosis 2013.

NIPT

SNP analysis T21/18/13 + sex chromosome aneuploidies + Di-George Syndrome

Accessible via Sonic Genetics Clinpath laboratories, Adelaide Womens Imaging, Specialist Imaging Partners

Available from 10 weeks gestation

5-8 business days till result return

Overall 1% test failure rate after redraw

Cost:$425 for the detection of trisomy 13, 18 or 21$495 for trisomy analysis and 22q11.2 deletionNo additional charge for sex chromosome aneuploidies or fetal sex determinationNo additional charge for a twin or IVF pregnancy.

https://www.sonicgenetics.com.au/nipt/doctors/

Norton et al. Cell-free DNA Analysis for Noninvasive Examination of Trisomy. NEJM 2015

Harmony

Aneuploidy screening – T21/18/13/sex chromosomes

Massive parallel sequencing technique

Available from 10 weeks gestation

3-5 business day results return

Test failure rate 0.1%

Lower FF threshold

Cost: $445

Accessible at Repromed locations

http://nestscreen.com.au/health-professionals/

Nest Results

Current program – first trimester screen

Correct dating

Information about multiples

Anatomy assessment

Increased NT marker for other structural anomaliesEsp cardiac

Low Papp-A Marker for IUGR etc

Potential to screen for pre-eclampsia

NIPT is not a replacement for 11-13 week scan + blood

Incorporation into clinical practice

Will be influenced by

Patient and doctor awareness

Cost and availability

First step

An option instead of invasive testing in case of high risk first trimester screen

Another option

Routine NIPT AND routine 12 week scan

Expensive

Contingent screening??

First trimester screen first then NIPT for intermediate risk group

Elective NIPT from 10 weeks?

Informed patient choice

Still need nuchal translucency ultrasound

If high risk result must have amnio or CVS for diagnosis

Missed first trimester screening

Advanced maternal age

Infertility

Recurrent miscarriages

Anxiety

Previous affected baby with trisomy 21, 18, 13

RANZCOG College Statement (2018)

“Women who choose to have cfDNA as a primary screening test should still be

offered the opportunity to have an 11-13 week ultrasound for an early structural

assessment, as 50% of major abnormalities can now be detected at this gestation”

When US abnormalities are present

Cytogenetic Abnormalities missed by NIPT 16.3%

Triploidy 4.2%

Mosaic 4.0%

Duplication/deletions 5.2%

Other 2.1%

Reimers RM et al. Prenatal Diagnosis. 2018.

Proposed algorithm

Low risk < 1/250

High Risk 1/50 to 1/250

High risk ≥ 1/50 OR≥ 1/250 and NT ≥

3.5mm

Morphology USS

Offer NIPT

Invasive Procedure

10+6 to 13+6 weeks

First Trimester Screening

Ultrasound

NT

PAPP-A

BhCG

NT ≥ 3.5mm

– Tertiary Morphology USS

PAPP-A < 0.3MoM

– Uterine artery dopplers

– Growth USS

Take home messages

The purpose of first trimester screening is to offer first trimester diagnosis and decision making

Offer to all women, but is an optional test

Current recommendation – combined FTS with serum screening + USS

Make sure SAMSAS form is filled correctly – can always ring and recalculate risks

If high risk result refer to tertiary centre for counselling

Refer to the South Australian GP Obstetric Shared Care Protocols 2017 – available online via SA PPGs

Contact your regional Shared-Care Coordinator

Take home messages

Non-Invasive Prenatal Testing

•Good test (Sensitivity; T21 99.9%, T18 98%, T13 80%)

•Low false positive rates

•High risk results still need invasive test

•Cost coming down

•Test failure - 0.1 – 3% (higher if weight > 140kg)

Still need 11-13 week ultrasound

with nuchal translucency + bloods

Thank you