1) The document discusses preimplantation genetic screening (PGS), which is used to test embryos for genetic abnormalities before implantation. PGS can be used to screen for conditions like cystic fibrosis or chromosomal abnormalities. 2) The document discusses different methods that can be used for PGS, including next generation sequencing, array comparative genomic hybridization, and quantitative PCR. It also discusses challenges with techniques like mosaicism rates and differences between biopsy sites. 3) The document reviews several studies that have investigated the use of PGS for different patient groups and clinical indications. These include women with advanced maternal age, recurrent pregnancy loss, repeated implantation failure, and previous aneuploid conceptions. The studies examined

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Preimplantation Genetic
Screening
Dr Tevfik Yoldemir
Marmara Üniversitesi Tıp Fakültesi
Kadın Hastalıkları ve Doğum A.D.
Üreme Endokrinolojisi ve İnfertilite B.D.
tevfik@yoldemir.com
consolidated approach for single
(or a few) cell genetic analysis
– i) standardization of the analytical methods,
– ii) analysis of cost-effectiveness, and
– iii) application of emerging technological
advances.
Systems Biology in Reproductive Medicine, 2012, 58: 289–300
Preimplantation genetic diagnosis is
currently indicated
• autosomal recessive diseases in which both parents
are known genetic carriers (cystic fibrosis, Tay-Sachs
disease, and sickle cell disease),
• autosomal dominant diseases in one or both parents
(Huntington’s disease),
• genetic mutations causing important consequences
(BRCA gene),
• X-linked diseases (hemophilia),
• certain balanced chromosomal translocations or
inversions.
Journal of Equine Veterinary Science 41 (2016) 29–34 Journal of Equine Veterinary Science 41 (2016) 29–34
Biopsy methods
Taiwanese Journal of Obstetrics & Gynecology 53 (2014) 146-150

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chromosomal mosaicism
• A systemic review by van Echten-Arends et al showed
that the rate of chromosomal mosaicism of cleavage
embryos appears to be as high as 72%.
• Even at the blastocyst stage, Fragouli et al
demonstrated that 32.4% of blastocysts are mosaic.
• Mosaic diploid- aneuploid blastocysts with >30%
normal cells account for <6% of the analyzed
embryos.
• Although meiotic and postzygotic errors leading to
mosaicism are common, most mosaic blastocysts
contain no normal cells.
Taiwanese Journal of Obstetrics & Gynecology 53 (2014) 146-150
chromosomal mosaicism
• Data report the rate of mosaicism at the cleavage
stage of development to be as high as 50 %. While
mosaicism does persist at the trophectoderm stage,
the rate of mosaicism is markedly lower,
approximating 3-5 %, than that at earlier stages of
development.
J Assist Reprod Genet (2016) 33:823–832
Methods used for molecular
analysis of all 24 chromosomes:
• metaphase comparative genomic hybridization (Wells et al.,
1999);
• array comparative genomic hybridization (aCGH) (Wells et
al., 2008; Geraedts et al., 2011);
• genome wide single nucleotide polymorphism analysis
(Harper and Harton, 2010);
• PCR-based detection (Treff et al., 2012) and
• next generation sequencing (NGS), or massive parallel
sequencing (MPS), using different platforms such as the
MiSeq (Fiorentino et al., 2014), the HiSeq platform (Wang et al., 2014)
or the IonTorrent platform (Kung et al., 2015).
Different techniques
J Assist Reprod Genet (2016) 33:823–832
Trophectoderm biopsy at blastocyst stage
• (i)inter-laboratory congruity and
• (ii) intra-embryo congruity of multiple embryo
biopsies in a single laboratory
• Only 2/11 (18.2 %) embryos were identically
assessed at two PGS laboratories;
• 4/11 (36.4 %), on repeat analysis were
chromosomally normal,
• 2 mosaic normal/abnormal, and 5/11 (45.5 %)
completely differed in reported aneuploidies.
• In intra-embryo analyses, 5/10 (50 %) differed
between biopsy sites. Gleicher et al. Reproductive Biology and
Endocrinology (2016) 14:54
next-generation sequencing (NGS)
• copy number analysis for all 24 chromosomes in
single or small numbers of cells, such as biopsies
from preimplantation embryos.
• array comparative genomic hybridization (aCGH),
• single-nucleotide polymorphism microarrays (SNP) ,
• and quantitative polymerase chain reaction (Q-PCR) .
• the focus in the PGS field has now shifted from day 3
single blastomere biopsy to day 5/6 trophectoderm
(TE) sampling
Zheng et al. Molecular Cytogenetics (2015) 8:38

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next-generation sequencing (NGS)
• Chromosomal copy number assessment based on
NGS may offer several advantages to aCGH including
reduced DNA sequencing cost, enhanced detection
of partial or segmental aneuploidies as a result of the
potential increase in chromosomal analysis
resolution, the potential automation of the
sequencing library preparation to minimize human
errors, reduce hands-on time, and enable higher
throughput and consistency
Zheng et al. Molecular Cytogenetics (2015) 8:38
Comprehensive chromosome screening
improves embryo selection
NGS vs aCGH
Zheng et al. Molecular Cytogenetics (2015) 8:38

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Clinical indications (n = 138)
PGS with array CGH screening
• 1) unexplained recurrent pregnancy loss (URPL):
patients (n = 71) with two or more unexplained
miscarriages;
• 2) repeated implantation failure (RIF): patients (n = 32)
with implantation failure after three or more IVF cycles
or with transfer of 10 or more good morphology
embryos; and
• 3) previous aneuploid conceptions (PAC): patients (n =
35) with one or more previous aneuploid conceptions
(e.g. Down Syndrome).
BMC Med Genomics. 2014 Jun 22;7:38.
Clinical indications
• advanced maternal age (AMA), usually defined as
maternal age above 35–38 years,
• repeated implantation failure (RIF) usually defined as
three or more transfers of morphologically high-
quality embryos without the establishment of
pregnancy,
• recurrent miscarriage (RM) in patients with normal
karyotypes (usually at least three previous
consecutive miscarriages)
• and severe male factor infertility (usually defined as
abnormal semen parameters).
Molecular Human Reproduction, 2016; Vol.22, No.8 pp. 539–544,
Women with unexplained RPL
• The IVF/PGS strategy had a live-birth rate of 53% and
a clinical miscarriage rate of 7%. Expectant
management had a live-birth rate of 67% and clinical
miscarriage rate of 24%.
• The IVF/PGS strategy was 100-fold more expensive,
costing $45,300 per live birth compared with $418
per live birth with expectant management.
Fertil Steril 2015;103:1215–20.
Decision making
Fertil Steril 2016;105: 188–93.
PGS - aneuploidy
Fertil Steril 2016;106: 75–9.
PGS - RCTs
Reproductive BioMedicine Online (2015) 30, 281–289

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Reproductive BioMedicine Online (2015) 30, 281–289
TE biopsy and PGS using aCGH
(40-43 years)
J Assist Reprod Genet (2015) 32:435–444
TE biopsy and PGS using aCGH
(40-43 years )
J Assist Reprod Genet (2015) 32:435–444
IR / LBR
J Assist Reprod Genet (2015) 32:435–444
PGS vs Expectant management
Human Reproduction, Vol.31, No.8 pp. 1668–1674, 2016
• PGS is to be strongly recommended when RPL is
associated with miscarriages during infertility
treatments, chromosomopathy in a previous
miscarriage, up to five previous miscarriages and a
high incidence of chromosomal abnormalities in
spermatozoa.
RBMonline Vol 18 No 5. 2009 687-693.

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PLoS ONE 10(10): e0140779. doi:10.1371/journal.pone.0140779 PLoS ONE 10(10): e0140779. doi:10.1371/journal.pone.0140779
PLoS ONE 10(10): e0140779. doi:10.1371/journal.pone.0140779 PLoS ONE 10(10): e0140779. doi:10.1371/journal.pone.0140779
PLoS ONE 10(10): e0140779. doi:10.1371/journal.pone.0140779 PLoS ONE 10(10): e0140779. doi:10.1371/journal.pone.0140779

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Fertil Steril 2016;106:597–602
The impact of contemporary PGS
• the analyzed and reanalyzed Centers for Disease Control data,
were not adequate to allow meaningful conclusions regarding
the contemporary practice of PGS.
• Randomized controlled studies and cohort studies have been
mainly from high quality laboratories in good prognosis
patients and showed no apparent adverse effect of biopsy.
• Whether similar good outcomes can be achieved in a wide
range of IVF settings and in patients with lower prognosis
remains to be established.
• Deferred transfer likely has specific advantages for PGS cycles
and timing and regimens for endometrial preparation are
certain to be further optimized and perhaps even matched to
embryo manipulation and quality.
• Intention to treat studies of deferred ET with and without
PGS and eventually of all transferred embryos will be required
3G technologies
• 3G high-throughput NGS technologies are expected to
offer advantages over 2G NGS, namely:
– 1) higher throughput;
– 2) longer read lengths;
– 3) higher accuracy;
– 4) less starting DNA;
– 5) faster turnaround time;
– 6) lower cost.
• However, as found in 2G technologies, data analysis is
still complex, owing to large data volume. In addition,
3G technologies need to solve signal-processing
challenges. Fertil Steril 2013;99:1054–61.
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tevfik@yoldemir.com