C620R9029.rtf

Blastocysts : Pros and Cons

D.K. Gardner

Colorado Center for Reproductive Medicine, Denver, Colorado, U.S.A.

Blastocyst culture is not a new technology. Indeed the first IVF pregnancy was conceived following blastocyst transfer, although it ended in a spontaneous abortion (1). Several investigators have discussed the potential advantages of blastocyst transfer (2;3;4). However, with the use of a single medium formulation, with or without coculutre, blastocyst transfer did not significantly increase implantation rates compared to those obtained following embryo transfer on day 3, and has therefore not been embraced by the IVF community. In contrast, the relatively recent introduction of sequential culture media (5) has led to increases in blastocysts implantation rates (6;7;8). Therefore there is renewed attention on the role of the human blastocyst in IVF.

The potential advantages of blastocyst culture and transfer include:

·  The ability to identify those embryos with limited developmental potential, because not all sperm or oocytes are destined to form viable embryos.

·  Synchronization of embryonic stage with the female tract thereby reducing cellular and nutritional stress on the embryo.

·  Minimize exposure of embryos to hyperstimulated uterine environment.

·  Uterine contractions are reduced by day 5 thereby reducing the chance of an embryo being expelled.

·  The ability to undertake cleavage stage embryo biopsy without the need for cryopreservation when the biopsied blastomere has to be sent to a different locale for analysis.

·  Assessment of true embryo viability by assessing the embryo post genome activation.

·  Culmination of the above is high implantation rates, thereby reducing the need to transfer multiple embryos.

·  Blastocyst stage embryos freeze as well, if not better, than cleavage stage embryos.

In contrast the potential disadvantages of blastocyst culture and transfer are:

·  Patient may not have an embryo suitable for transfer

·  Requires more incubators / laboratory space

The question is therefore raised, are there specific indications for patients to have extended culture and blastocyst transfer, or should extended culture be performed on all patients?

The use of sequential culture media to support human blastocyst development was initially offered to patients with either a good response to gonadotropins (6;7;9) or with >4 eight-cell embryos on day 3 (8). This approach for good prognosis patients led to a significant increase in implantation rates and facilitated the establishment of high pregnancy rates (70%) with a concomitant reduction in the number of embryos transferred. Therefore the use of sequential culture media to facilitate blastocyst transfer has led to a significant reduction in the number of high order multiple gestations and subsequently should be considered as the primary treatment for patients who respond well to gonadotropins.

Sequential media and blastocyst transfer have now been used successfully to treat patients with poor quality embryos (10;11), patients with multiple IVF failures (12), patients with low numbers of oocytes and embryos (13, 14), patients at risk of ovarian hyperstimulation syndrome (15) and oocyte donors (16). In all of the situations listed extended embryo culture has been associated with an increase in IVF success rates, although a smaller number of reports have questioned such benefits (17; 18; 19).

So can blastocyst culture and transfer be applied to all patients entering IBF treatment? In two retrospective studies, in which all patients attending fertility treatment underwent blastocyst culture and transfer, it was determined that extended culture resulted in increased implantation and pregnancy rates, compared to the use of cleavage-stage embryo transfer (13;20). Although there was a significant increase in the percentage of patients who did not have an embryo transfer on day 5 in one report (6.7%, compared to 2.9% of patients having a day 3 transfer) (20), pregnancy rates per oocyte retrieval were higher for day 5 transfers (57.5%) compared to day 3 transfers (46.1%). Furthermore, the number of embryos transferred on day 5 was significantly below that transferred on day 3 in both reports (13;20).

Conclusions

Blastocyst culture and transfer represents an effective means of eliminating high order multiple gestations in good prognosis patients. Certainly blastocyst transfer, with resultant high implantation rates, should be considered for patients electing to have a single embryo transferred (21).

There are other practical advantages associated with blastocyst transfer, such as the ability to perform embryo biopsy at the cleavage stage and send the sampled cell to a different laboratory for analysis. The embryo can then be cultured to the blastocyst stage without compromising its viability while the genetic tests are performed.

Blastocyst stage embryos can be cryopreserved effectively. Therefore when using the following equation (22) to estimate IVF efficacy, blastocyst transfer has been calculated more effective than the transfer of cleavage stage embryos.

(mean number of embryos transferred x implantation rate)

+

(mean number of embryos cryopreserved x implantation rate)

x

(1 – no transfer rate)

The main disadvantage perceived is that there will be more patients without an embryo transfer following extended culture. While this has been shown to be the case (20), the overall pregnancy rate per retrieval on day 5 was still significantly higher than that obtained on day 3. It has therefore been proposed that patients who do not have a morula or blastocyst to transfer on day 5 or 6 would not have conceived following a day 3 transfer and therefore extended culture can be used as a diagnostic tool (23).

Finally, it would be unwise to suggest that blastocyst culture and transfer represents a panacea for all clinics and all patients. Before extended culture should be considered, all aspects of clinical and laboratory procedures need to be optimized. Should problems exist either in patient stimulation protocols or within the laboratory, extended culture may only exacerbate the situation. Extended culture should first be tried on oocyte donors, or those patients who respond well to gonadotropins. Implantation rates of 40% or greater should readily be obtained in such patients. Should such implantation rates not be attained then a thorough analysis of the laboratory, patients’ stimulation and luteal support regimens should be undertaken.

References

1.  Edwards,R.G. (1995) Principles and Practice of Assisted Human Reproduction, Eds. Edwards,R.G. and Brody,S.A. W.B.Saunders, Philadelphia.

2.  Menezo,Y., et al. (1990) Biol Reprod., 42, 301-306.

3.  Bolton,V.N., et al. (1991) Fertil Steril. 55, 830-832.

4.  Lopata,A. (1992) J Assist Reprod Genet. 9, 509-512.

5.  Barnes,F.L. et al., (1995) Hum Reprod.10, 3243-3247.

6.  Gardner,D.K., et al., (1998) Fertil Steril. 69, 84-88.

7.  Gardner,D.K. et al., (1998) Hum Reprod. 13, 3434-3440.

8.  Milki,A.A., et al. (1999) Fertil Steril. 72, 225-228.

9.  Karaki,R.Z. et al., (2002) Fertil Steril. 77, 114-118.

10.  Langley,M.T., et al., (2001) Hum Reprod. 16, 902-908.

11.  Balaban,B., et al., (2001) Fertil Steril. 75, 514-518.

12.  Cruz,J.R., et al., (1999) Fertil Steril. 72, 218-220.

13.  Wilson,M., et al., (2001) Fertil Steril. 77, 693-696.

14.  Vlaisavljevic, V. et al., (2001) Hum Reprod. 16, 2379-2383.

15.  Trout,S.W. et al., (2001) Fertil Steril. 75, 1066-1067.

16.  Schoolcraft,W.B., Gardner,D.K. (2000) Fertil Steril. 74, 482-486.

17.  Coskun,S., et al., (2000) Hum Reprod. 15, 1947-1952.

18.  Racowsky,C., et al., (2000) Fertil Steril. 73, 558-564.

19.  Alikani,M., et al., (2000) Hum Reprod. 15, 2634-2643.

20.  Marek,D., et al., (1999) Fertil Steril. 72,1035-1040.

21.  Hunault,C.C. et al., (2002) Fertil Steril. 77, 725-732.

22.  Gardner,D.K., et al., (2000) Hum Reprod. 15, Supplement 6, 9-23.

23.  Doody,K.J. (2001) ART and the Human Blastocyst, eds. Gardner,D.K. and Lane,M. Springer Verlag, New York. 167-183.