Implantation and Pregnancy Rates of Day 5 Compacted, Cavitated and Inferior Blastocyst Transferred Embryos

Introduction: The trend in the last years is to culture all embryos to the blastocyst stage and transfer them on Day 5 to increase implantation rates. Since Day 5 embryos are in different stages of development (compacted, cavitated, early blastocyt and expanded one), their implantation potential is unclear.

Aim: To evaluate the implantation potential and pregnancy rate of delayed stages of embryo development on day 5, compared with blastocyst and analyze the characteristics of those which implanted.

Material & Methods: A retrospective study was conducted between the years 2014-2016 in 142 patients whose transfer was on day 5 of embryo development. All patients had at least 8 retrieved mature oocytes. Embryos were cultured in sequential media (G1, G2 Vitrolife, Sweden). All incubators were adjusted to low oxygen concentration (6.0% O2). Embryo evaluation was performed at the same time. When 2 embryos of different developmental stage were transferred, the one which was more advanced in its development was considered as the implanted. The second group included 100% implantation cycles. All implanted embryos were divided into 4 groups according to their quality (Gardner`s criteria). Group 1: top quality (4-5AA); Group 2: early blastocysts; Group 3: intermediate (4AB, 4BA, 4BB); and Group 4: inferior (4BC, 4CB, 4CC or compacted).

Results: We performed 142 cycles, 46 were SET ones. All transfers were conducted on day 5. In Most cycles we performed ICSI unless sperm quality was good enough for IVF. Female age was 30.7±4.84. Only one patient didn’t have transfer. In some cases we transferred compacted or cavitated stages because no blastocysts developed. Blastulation rate was 711/1532 (46.4%) in ICSI embryos and 132/189 (69.8%) in IVF embryos. From 141 transfers we obtained 62 pregnancies (44%); 50 singletons (81%), 11 twins (18%) and 1 triplet (1%). The missed abortion rate was 9.7%. One missed abortion was of a pregnancy resulted from a single compacted embryo transfer, another of 2 early blastocysts transfer, the rest were of blastocysys of intermediate quality.

In total 75/272 transferred embryos implanted (27.6%); 61 of 186 transferred blastocysts implanted (32.8%) and 14 of 86 embryos delayed in development (16.3%) meaning: 6/20 early blastocysts (30.0%), 4/31 cavitated (12.9%) and 4/35 compacted embryos (11.4%). Implantation potential of compacted and cavitated stages were significantly lower than the blastocyst stages (P<0.05).

In 33 cycles, 48 embryos implanted (100% implantation cycles). According to embryo quality: 29.2% top quality blastocysts implanted, 18.8% early blastocysts, 39.6% blastocysts of intermediate morphology and 16.7% of inferior quality.

Conclusions: Inferior blastocysts quality or delayed in development contribute to pregnancy rate, therefore, it is recommended to transfer them, although their implantation rate is significantly lower.