Biopsy
Clinical pregnancy rate per transfer
Ongoing pregnancy rate per transfer
Implantation rate per transfer
References
Polar bodya
33 % (8/24)
29 % (7/24)
26 % (10/39)
[31]
35.2 % (38/108)
27.7 % (31/108)
27.7 % (31/112)
[29]
43 % (3/7)
43 % (3/7)
40 % (4/10)
[30]
Day 3 blastomere
Unknown
54 %
39 %
[40]
81.8 % (27/33)
72.7 % (24/33)
52.63 % (30/57)
[11]
60.3 % (123/204)
53.9 % (110/204)
53.5 % (161/301)
[39]
TE from blastocyst
70.9 % (39/55)
69.1 % (38/55)
70.9 % (39/55)
[41]
70.2 % (26/37)
70.2 % (26/37)
63.5 % (33/52)
[10]
58.8 % (20/34)
Unknown
54.3 % (25/46)
[12]
Unknown
67 %
61 %
[40]
Single Embryo Transfer After Biopsy and aCGH
Limited data are available on the clinical outcome with single embryo transfer after polar body biopsy and DNA microarray analysis. After polar body biopsy and DNA microarray analysis, the resulting euploid embryos may be transferred fresh on day 3 at cleavage stage or days 5 and 6 at blastocyst stage. They could also be frozen for a later frozen embryo transfer. So a comparison of efficacy is more difficult due to these numerous factors. Based on our experience with a limited number of cases (n = 55) of frozen single blastocyst transfer in which the embryos were biopsied and tested with DNA microarray at the blastocyst stage, the clinical pregnancy rate was as high as 63.6 % in women of advanced ages (37–42 years old) during 2012. The rate is comparable to the rates with fresh single blastocyst transfer (19/38, 50 %) and frozen–thawed single blastocyst transfer (122/222, 55 %) in young patients (<35 years old) without aneuploidy screening. These results were also comparable to multiple embryo transfer in our clinic. These results indicate that aneuploidy screening by aCGH is helpful for patients of advanced maternal age to obtain high pregnancy rates and single euploid blastocyst transfer is recommended.
As polar body biopsy is a noninvasive procedure and theoretically and practically it is safer than blastocyst biopsy, it would be possible to get the same pregnancy rate if the biopsy is properly done in the oocyte and zygote stage, and the resulting embryos were transferred at later stages. However, because blastocyst development rates of human eggs obtained from patients undergoing ART are 50–60 %, it is suggested that single embryo transfer should be performed after the embryos develop to blastocyst stage (i.e., biopsy should not be performed on day 3 cleavage stage or earlier stages). The single embryo transfer can be done with either fresh or frozen blastocysts. Similar pregnancy and implantation rates should be obtained with fresh and frozen blastocyst transfer as blastocyst cryopreservation by vitrification does not affect the embryo survival with the optimized protocol.
Conclusions
DNA microarray technology has revolutionized life science research and medical diagnosis. Its application in PGS has brought about great improvement to the success of human ART. However, due to the complexity of various aneuploidies and chromosome mosacism in cleavage embryos and blastocysts, it is difficult to examine all chromosome abnormalities by a single PGS approach. For different patients and different situations, different PGS procedures should be applied in order to get the best clinical results. Although the blastocyst stage is now considered to be the optimal embryo stage to perform biopsies for PGS, polar body biopsy technology, for its noninvasive nature (and earlier PGS result availability), may be worthy of consideration in patients with few eggs and further embryo culture and/or blastocyst transfer is not necessary. Further randomized clinical trials are required to confirm the clinical value of polar body analysis for the improvement of clinical outcomes.
Conflict of Interest
The authors declare no conflict of interest.
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