2. Limitations of conventional embryo screening techniques
Cells are in interphase
- use FISH
Limited range of fluorochromes
Less than half the chromosomes tested
Spreading requires skill and can be inconsistent
Mosaicism
Poses a significant problem for diagnosis.
However, most mosaic cleavage stage
embryos are aneuploid in every cell.
Cleavage stage biopsy may represent a cost to the
embryo
3. Comparative genomic hybridization- CGH
• Technique related to FISH
• Allows the copy number of every chromosome to be determined
Chromosome 15
Test DNA Normal DNA
Normal Trisomy Monosomy
Gain
Loss
Normal
Kallioniemi et al 1992;
Wells et al 1999, 2002; Voullaire et al 1999; Wilton et al 2001; Gutierrez et al 2004, 2005; Fragouli et al 2006, 2007
4. Embryo screening using CGH
Benefits
• All chromosomes tested
• DNA-based
• No spreading of cells on slides
But what about mosaicism and the impact of biopsy?
5. Comprehensive chromosome screening of blastocysts
Trophectoderm biopsy-
3-10 cells (mean 5) biopsied and tested
Courtesy of M. Katz-Jaffe and J. Stevens, CCRM
6. Comprehensive chromosome screening of blastocysts
Analysis of blastocyst stage
• Biopsy of several cells is possible
Diagnosis more robust and accurate
Less risk of misdiagnosis due to mosaicism
Reduced impact of embryo biopsy
• Blastocyst cryopreservation (vitrification) necessary
• Can overcoming the principal challenges to accurate screening
allow PGS to fulfill the potential predicted by theory?
7. Blastocyst CGH- clinical results
• 170 patients, mean age 38 years, 1-6 previous failed IVF cycles
(mean 2)
• Near 100% survival after biopsy, freeze and thaw
• Pregnancy rate per cycle with transfer 87%
• Birth rate per cycle with transfer 79%
• Implantation rate per embryo 67%
72%
60%
28% *
Control group matched for: maternal age, day-3 FSH, day of transfer, # oocytes
retrieved, # of failed cycles
*p<0.0003 - Extremely promising for single embryo transfer
8. Blastocyst CGH- rates of pregnancy loss
• Embryo loss rates are low
• 91% of embryos that produced a fetal sac resulted in an
ongoing third trimester pregnancy or live birth
• 97% of embryos that produced a fetal heart beat resulted in an
ongoing third trimester pregnancy or live birth
• Expected pregnancy loss rate for IVF patients in this age
range is ~25%
9. Blastocyst CGH- Pregnancy rates
100
90
80
70
60
50
40
30
20
10
0
30-34 35-38 39-42 43-50
Positive pregnancy
per transfer
Positive pregnancy
per cycle with biopsy
Pregnancy rate per transfer shows only a small decline with advancing age
Pregnancy rate per cycle shows a significant decline
10. Blastocyst CGH- aneuploidy and implantation rates
Why does age still lead to reduced pregnancy rates despite aneuploidy
screening?
100
90
80
70
60
50
40
30
20
10
0
30-34 35-38 39-42 43-50
Implantation rate
Aneuploidy rate
Cycles with all embryos
aneuploid
11. Conclusions
• Pregnancy rates were above those typically achieved for all age
groups.
• However, pregnancy rates were lower for older patients due to
the increased frequency of cycles with no euploid embryos.
• Chromosomally normal embryos from older patients have a
similar chance of producing a child as those derived from
young patients.
• Aneuploidy is likely to be the principal factor causing reduced
IVF success with advancing maternal age
• Spontaneous abortion rates were reduced for all patients,
including those with a history of multiple miscarriage
12. Questions
• Can the results obtained in the current study be replicated in a
randomized controlled trial?
• An RCT is currently underway
• What patient groups will benefit the most from this type of
screening?
• Young patients may benefit, particularly in countries where
single embryo transfer is mandatory
13. United Kingdom (Oxford)
Elpida Fragouli
Samer Alfarawati
United States (Livingston, NJ)
Pere Colls
Tomas Escudero
N-neka Esprit-Ngachou
Jill Fischer
Cristina Gutierrez-Mateo
Santiago Munne
Renata Prates
Jorge Sanchez
Sophia Tormasi
John Zheng
Colorado Center for
Reproductive Medicine
Mandy Katz-Jaffe
Dagan.Wells@obs-gyn.ox.ac.uk
John Stevens
Bill Schoolcraft
