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A comparison of pregnancy rates of frozen embryo transfers of vitrified blastocysts to vitrified euploid blastocysts


To compare the pregnancy rates of frozen (vitrified) blastocyst transfers to the transfers of vitrified euploid blastocysts.


Retrospective study in a private assisted reproductive technology program.


Pregnancy rates for transfer of vitrified blastocysts were compared with those of euploid vitrified blastocysts in a total of 448 embryo transfer cycles. A total of 94 euploid embryos and 354 frozen embryo transfers (FET) were performed. All embryos were cultured in Continuous Single Culture Media (Irvine Scientific) to the blastocyst stage. The embryos were vitrified dependent on freeze quality (grade CC or higher). The embryos that underwent preimplantation genetic screening (PGS) were laser assist-hatched on day 3, then biopsied once they reached hatching with a differentiated inner cell mass and trophectoderm. All blastocysts were collapsed prior to freezing. Vitrifcation and warming were performed using Irvine Scientific freeze and thaw kits and Cryolocks. Patients who used donor eggs were excluded from this study. The outcomes of interest were positive hCG and positive clinical pregnancy rates (defined as the presence of fetal activity at 7 weeks).


A total of 253 of the 354 (71%) FET patients had a positive hCG compared to 61 of the 94 (67%) of euploid FET patients. Of the FET patients, 182 (of 354) developed fetal cardiac activity at their 7 week ultrasound, resulting in 51% clinical pregnancy rates. In comparison, 35 (of 94) patients who transferred euploid embryos developed fetal cardiac activity, resulting in 53% clinical pregnancy rate. Statistical analysis by t-Test demonstrated no significant difference between standard frozen embryo transfer and transferring frozen euploid embryos.


Vitrified blastocyst that reach freeze quality have no significant difference in positive hCG or clinical pregnancies compared to transferring vitrified euploid embryos. These results may be indicative that biopsy may impact the ability of the embryo to implant or develop. Also, the criteria of the embryos that are biopsied is not as consistent as what is classified as “freeze quality”. This flexibility in grading may be detrimental to the embryo’s ability to survive the biopsy and subsequent transfer.

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