UOG Journal Club: Fetal fraction in maternal plasma cell-free DNA at 11–13 weeks’ gestation

$Page 1: UOG Journal Club: Fetal fraction in maternal plasma cell-free DNA at 11–13 weeks’ gestation$
UOG Journal Club: January 2013Fetal fraction in maternal plasma cell-free DNA at 11–13 weeks’

gestation: relation to maternal and fetal characteristics

G Ashoor, A Syngelaki, LCY Poon, JC Rezende and KH NicolaidesVolume 41, Issue 1, Date: January 2013, pages 26–32

Journal Club slides prepared by Dr Asma Khalil (UOG Editor for Trainees)

Chiu RW et al., BMJ 2011; Chen EZ et al., PloS One 2011; Ehrich M et al., AJOG 2011; Palomaki GE et al., Genet Med 2011; Palomaki GE et al., Genet Med 2012; Ashoor G et al., AJOG 2012; Bianchi D et al., Obstet Gynecol 2012; Norton ME et al., AJOG 2012; Sparks AB et al., AJOG 2012

Trisomy 21 Trisomy 18 Trisomy 13

DR FPR DR FPR DR FPR

Chiu et al. 2011 100% 2.1%

Chen et al. 2011 91.9% 2% 100% 1.1%

Ehrich et al. 2011 100% 0.2%

Palomaki et al. 2011 98.6% 0.2%

Palomaki et al. 2012 100% 0.3% 91.7% 1%

Ashoor et al. 2012 100% 0% 98% 0% 80% 0.05%

Bianchi et al. 2012 98.9% 0% 92.1% 0% 68.8% 0%

Norton et al. 2012 100% 0.03% 97.4% 0.07%

Sparks et al. 2012 100% 0% 100% 0%

DR, detection rate; FPR, false positive rate

Screening by cell-free (cf) DNA testing of maternal blood in high-risk populations:

Background

Nicolaides KH et al., AJOG 2012Ashoor G et al., UOG 2013

Detection rate False positive rate

Trisomy 21 99.5% 0.1%

Trisomy 18 92–100% 0–0.3%

Trisomy 13 68–100% 0–1.1%

Screening by cfDNA testing of maternal blood in low-risk populations:

Background

Strengths

• Highly accurate in the detection of trisomies 21 and 18 and to a lesser degree trisomy 13

• The screening performance for trisomies 21 and 18 is far superior to that of all currently available screening methods (DR>99% and FPR <1%)

Limitations

•The main limiting factor currently is the high cost

• Fails to provide results if the fetal fraction < 4%

Background

Non-invasive prenatal testing (NIPT)

Fetal fraction in maternal plasma cell-free DNA at 11–13 weeks: relation to maternal and fetal characteristics

Ashoor et al., UOG 2013

Objectives

• Examine the possible effects of maternal and fetal characteristics on the fetal fraction in maternal plasma cfDNA at 11–13 weeks

• Estimate the proportion of pregnancies at high risk of NIPT failure because the fetal fraction is < 4%



• Prospective first-trimester screening for aneuploidies and adverse pregnancy outcomes in singleton pregnancies (n=1,949)

• Stored maternal plasma at −80 °C • Collected in ethylenediamine tetraacetic acid BD vacutainer TM tubes • Centrifuged at 2000g for 10min and subsequently at 16 000g for 10min, within 15min of collection

Methodology

0

50

100

150

200

2.3 4.0 6.3 9.0 12.3 16.0 20.3 25.0 30.3Fetal fraction (%)

Fre

qu

en

cy

• The median fetal fraction was 10.0%• with weight• in Afro-Caribbean• with fetal CRL• 7.5% in smokers• 25.0% in trisomy 21

Results

0

5

10

15

20

25

Fet

al f

ract

ion

(%)

40 50 60 70 80 90 100 110 120 130

Maternal weight (kg)

140 150 160 170 180

99th

75th

50th

25th

97th

95th

90th

10th 5th 3rd 1st

4

Weight (kg)

Failure (%)

40 0.4

60 1.5

80 4.7

100 12.1

120 25.1

140 43.1

160 62.8

180 79.5

Results



Results

No significant contribution to fetal fraction from:

• Maternal age

• Fetal gender

• NT thickness

• Method of conception

• Linear association with free β-hCG and PAPP-A



Discussion

The inverse association between fetal fraction and maternal weight could be attributed to:

• Dilutional effect

• Accelerated turnover of adipocytes (releases cfDNA of maternal origin into the circulation thereby lowering the proportion of fetal cfDNA)



• NIPT is far superior to currently available screening methods. The greatest risk factor for low fetal fraction and failure is obesity. The opportunity for testing and counseling in the same visit is missed when NIPT fails.

• Alternatively, NIPT can be performed along with the combined screening blood test at 10-11 weeks. Hence results are available at the scan assessment, where CVS can be performed if high risk. Where NIPT fails, the parents would still have the first trimester combined test result.

• This policy might exaggerate the problem of low fetal fraction because it is done earlier when the CRL and fetal fraction are smaller

Implications for practice

Fetal fraction in maternal plasma cf-DNA is affected by

Maternal characteristics (weight, ethnicity, smoking)

Fetal characteristics (CRL, aneuploidy)



Conclusions

Discussion points• What maternal characteristics would influence the fetal fraction in maternal plasma cell-free

fetal DNA test after 14 weeks’ gestation?

• Apart from trisomy 21, what other fetal chromosomal abnormalities would influence the fetal fraction in maternal plasma cell-free DNA in multiple pregnancies?

• Can we offer the non-invasive prenatal testing (NIPT) using cell-free fetal DNA to twin pregnancies or pregnancies conceived using IVF with egg donation?

• What sort of NIPT result would be expected with placental mosaicism?

• Could invasive prenatal diagnosis be avoided with a low-risk NIPT result where the fetus has an isolated increased nuchal translucency?

• What impact would the introduction of NIPT as a screening tool have on the numbers of prenatal invasive tests performed?

• Would there be a role for first-trimester combined nuchal plus biochemistry testing if NIPT were used universally as a routine screening tool.

• What would be the management options for a woman that had fetal DNA in maternal plasma test when first seen at 11 weeks’ gestation, and who received a ‘failed’ result at 13 weeks?

Education

UOG Journal Club: Fetal fraction in maternal plasma cell-free DNA at 11–13 weeks’ gestation