Vitrified-warmed Blastocyst Transfers Found to have Similar Clinical Outcomes as Fresh Transfers

A vital component of any cryopreservation protocol used in ART is the minimal effect of the method on the preserved embryos. With its inherent benefits when compared to slow freezing, vitrification has been widely accepted worldwide and considering its widespread usage, numerous studies have evaluated the neonatal outcomes with encouraging results. Adding further credence to this technique, a recent retrospective study highlights that vitrified-warmed blastocyst transfers have equal live birth rates and enhanced neonatal outcomes in comparison to fresh transfers. The study findings are published in the journal, Fertility and Sterility.

Tammie K Roy, Principal Scientist at Genea, Sydney, Australia and coworkers compared the pregnancy and neonatal outcomes of 645 vitrified-warmed and 1,157 fresh single embryo transfers in 1209 infertile patients. Grade I and II embryos were used for day-5 blastocyst transfers. The findings showed that there was no significant variation in the blastocyst thaw survival rate (overall rate=94.4%) between blastocyst grades and developmental stages. Similar live birth rates (Grade I blastocysts=55.3% vs. 52.8%; Grade II=30.4% vs. 34.9%) were noted after vitrified-warmed blastocyst and fresh transfers, respectively. Vitrified-warmed blastocyst transfers were associated with substantially improved neonatal outcomes when compared to fresh cycles, as evident by average 0.3 weeks longer gestational age and average 145 gram heavier live birthweight of babies in the vitrification group. Based on the findings, the researchers concluded on the similar effectiveness of the vitrified-warmed blastocyst as the fresh transfers.

Similar findings were observed in an earlier study by Feng et al (Reproductive BioMedicine Online, 2012), wherein the corresponding clinical pregnancy rate was 46.1% and 52.15% for vitrified and fresh single blastocyst transfer. The researchers noted comparable clinical outcomes in terms of the rates of miscarriage, monozygotic twin, and ectopic pregnancy in both the groups. Moreover, there was no significant difference with respect to neonatal outcomes like premature delivery, low birthweight, live birth, and birth defect rates between fresh and vitrified blastocyst transfer. Besides, the results also showed that single blastocyst transfer using fresh or vitrified embryos was effective in decreasing multiple pregnancy rates.

A more recent retrospective study by Muthukumar et al (Journal of Human Reproductive Sciences, 2013) also reiterated the same findings. The study, conducted on 249 women, reported no significant variation in the live birth rate between vitrified warmed day 5/6 blastocyst and fresh day 5 blastocyst transfers. In the light of the findings, the scientists opined that vitrification of blastocysts using solid surface methodology was an efficient cryopreservation technique.

Zhu et al (Fertility and Sterility, 2011) demonstrated statistically significant increased clinical pregnancy (55.1% vs. 36.4%) and implantation rates (37.0% vs. 25.2%) after vitrified-warmed blastocyst transfers when compared to fresh cycles. The researchers further observed that rise in the success rates could be attributed to enhanced synchronization and endometrial receptivity in the natural cycles than stimulated cycles, wherein the levels of estradiol are supraphysiological. Considering this, they suggested a new embryo transfer method, wherein fresh blastocyst transfer should not be offered in the initial ovarian stimulation cycle, but all the blastocysts available may be vitrified-warmed and used in the subsequent transfers.

Due to the increased adoption of single blastocyst transfer (SBT) in assisted reproduction, reliable cryopreservation of the surplus blastocysts is in great demand. Although SBT has been found to decrease multiple pregnancies in fresh cycles, very few trials have evaluated its effectiveness in cryopreserved cycles. In view of the current study findings highlighting the comparable clinical outcomes of both fresh and vitrified-warmed blastocyst transfer, single blastocyst transfer in cryopreserved cycles may serve as a potential safe and effective method in routine clinical practice.

References

  • Roy TK, Bradley CK, Bowman MC, McArthur SJ. Single-embryo transfer of vitrified-warmed blastocysts yields equivalent live-birth rates and improved neonatal outcomes compared with fresh transfers. Fertil Steril. 2014 May;101(5):1294-1301.e2.
  • Feng G, Zhang B, Zhou H,et al. Comparable clinical outcomes and live births after single vitrified-warmed and fresh blastocyst transfer. Reprod Biomed Online. 2012 Nov;25(5):466-73.
  • Muthukumar K, Kamath MS, Mangalaraj AM, Aleyamma T, Chandy A, George K. Comparison of clinical outcomes following vitrified warmed day 5/6 blastocyst transfers using solid surface methodology with fresh blastocyst transfers. J Hum Reprod Sci. 2013 Jan;6(1):59-64.
  • Zhu D, Zhang J, Cao S, et al. Vitrified-warmed blastocyst transfer cycles yield higher pregnancy and implantation rates compared with fresh blastocyst transfer cycles–time for a new embryo transfer strategy? Fertil Steril. 2011 Apr;95(5):1691-5

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