1. a systematic review and meta-analysis
Analysis of cell-free fetal DNA in maternal blood for detection of trisomy 21, 18 and 13 in a general pregnant population and in a high risk population:
a systematic review and meta-analysis
ERIK IWARSSON1, BO JACOBSSON2,3, JESSICA DAGERHAMN4, THOMAS DAVIDSON4,5, EDUARDO BERNABE’6 & MARIANNE HEIBERT ARNLIND4,7
1Department of Molecular Medicine and Surgery, Clinical Genetics Unit, Karolinska Institutet, Karolinska University Hospital, Stockholm, 2Department of Obstetrics and Gynecology, Sahlgrenska Academy, Gothenburg University, Gothenburg, Sweden, 3Department of Genetics and Bioinformatics, Area of Health Data and Digitalisation, Institute of Public Health, Oslo, Norway, 4Swedish Agency for Health Technology Assessment and Assessment of Social Services (SBU), Stockholm, 5Division of Health Care Analysis, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden, 6Division of Population and Patient Health, King’s College London Dental Institute at Guy’s, King’s College and St Thomas Hospitals, London, UK, 7Medical Management Centre/LIME, Karolinska Institutet, Stockholm, Sweden
ACTA Obstetricia et Gynecologica Scandinavica Journal Club
January 2017
Edited by Francesco D’Antonio

2. Background
Aneuploidies are the major cause of perinatal death and childhood handicap and constitute the most common indication for invasive prenatal tests such as chorionic villus sampling and amniocenteses.
Invasive prenatal diagnosis is associated with a small but significant risk of miscarriage (0.1–0.5%).
Fetal cell-free DNA (cfDNA) obtained from maternal plasma allows non-invasive detection of fetal aneuploidies.
Non-invasive prenatal testing (NIPT) for fetal aneuploidy analysis using cfDNA was introduced clinically in 2011 and is implemented in many countries worldwide.
Data from large studies on test performance in a general (i.e. average-risk) pregnant population are lacking.

3. Aim of the study
To review the performance of NIPT for detection of trisomy 21, 18 and 13 (T21, T18 and T13) in a general pregnant population as well as to update the data on high-risk pregnancies.

4. Methodology
Study design: Systematic review and meta-analysis.
Methods:
Literature search: PubMed, Embase and the Cochrane Library ( ).
Inclusion criteria:
Pregnant women at high risk of carrying a fetus with chromosome aberration (according to biochemical screening, first trimester combined screening (FTS), abnormal ultrasound scan or maternal age).
Pregnant women at average risk of carrying a fetus with chromosome aberration, i.e. a general pregnant population.
Exclusion criteria: RNA analysis, absence of primary data, study population <100 women and abstract/letter/review.

5. Methodology
Reference standard: Invasive genetic testing or phenotype at birth.
Quality assessment of the included studies: Assessment of the quality of the quality of scientific evidence of the outcomes was rated according to the four GRADE levels: High (⊕⊕⊕⊕) – high chance that the true effect lies close to the estimated effect; Moderate (⊕⊕⊕Ο) –the true effect is likely to be close to the estimated effect, but there is a possibility that it is quite different; Low (⊕⊕ΟΟ) –the true effect may be substantially different from the estimated effect; Very Low (⊕ΟΟΟ) –the true effect is likely to be substantially different from the estimated effect.

6. Methodology
Statistical analysis:
Bivariate random-effects model was used to estimate average sensitivity, specificity, positive and negative likelihood ratios (LR+ and LR-) and diagnostic odds ratios (DOR), with 95% confidence intervals (CI). Summary receiver operating characteristics (SROC) curve and the corresponding area under the curve (AUC) to summarize overall test performance were also constructed.

7. Results (1) 32 studies (31 articles) 23 prospective cohort studies
9 case-control-studies
Majority of sampling performed in the first trimester
25 studied on a high-risk population
5 studies on an average-risk population
2 studies on both a high and an average-risk population
13 studies had a population exceeding 1000 pregnancies

8. Results (2)
Trisomy
Population
Probability
(“risk”)
Sample size
(no. of studies)
Sensitivity,
pooled estimates
(95% CI)
Specificity,
Quality of evidence
T21
High
(26)
0.998 (0.981–0.999)
0.999 (0.99–0.999)
(⊕⊕⊕Ο)
Average
(6)
0.993 (0.955–0.999)
0.999 (0.998–0.999)
T18
(22)
0.977 (0.958–0.987)
T13
(18)
0.975 (0.819–0.997)
0.999 (0.999–0.999)
(⊕⊕ΟΟ)
Quality of evidence for T21 and T18 was moderate in the high-risk population and for T21 in the average-risk population.
Quality of evidence for T13 was limited in the high-risk population. No meta-analysis or grading for T13 and T18 in the average-risk population was performed due to lack of data.

9. Results (3) False positives False negatives
Proportion of FP ranged between 2.7% (T21 in the high-risk population) and 30% (T13 in the general population). Proportion of FN was generally very low.
Evidence of publication bias for T21 in the high-risk (p = 0.001) and average-risk populations (p = 0.018), as well as for T18 in the high-risk population (p = 0.010).
No evidence of publication bias for T13 in the high-risk population (p = 0.085)

10. Limitations
High heterogeneity among the included studies
Significant publication bias
Heterogeneity in the definition of high risk population
Differences in NIPT technology
Lack of stratification according to ultrasound (i.e. increased nuchal translucency), biochemical (i.e. abnormal biochemical screening tests for aneuploidies) and maternal (i.e. advanced maternal age) characteristics

11. Conclusion
NIPT performs well as a screen for trisomy 21 in a general pregnant population. Although the false positive rate is low compared with first trimester combined screening, women should still be advised to confirm a positive result by invasive testing if termination of pregnancy is under consideration