Does low oxygen concentration affect blastocyst formation rate in PGD (preimplantation genetic diagnosis) cycles?

Abstract

OBJECTIVE: To evaluate the effect of culturing embryos from PGD cycles till day 5 of development in two different oxygen concentration conditions.DESIGN: Retrospective study of 252 PGD cycles.MATERIALS AND METHODS: A total of 937 embryos from Preimplantation Genetic Screening (PGS) cycles performed between October 2004 and October 2009 were included in the study. Cases formed two groups depending on whether embryos were cultured in atmospheric (∼ 20%) oxygen conditions (group 1 including 138 cycles), or in low (5%) oxygen concentrations (group 2 including 114 cycles). All embryos were cultured in Heracell® incubators at 37°C and 5% CO2. Biopsy of one or two cells from each good quality embryo were performed on day 3 and transfers occurred on day 5. FISH (Fluorescent In Situ Hybridization) analysis included chromosomes 13, 15, 16, 18, 21, 22, X and Y. Expanded and hatching blastocysts were graded for embryo quality considering inner cell mass and trophectoderm characteristics. Student's group t-test and chi-square analysis were used to analyze results.Tabled 1GROUP 1GROUP 2p-valueN embryos592511Blastocyst formation (%)53,649,6p=NSEarly blastocyst (%)2414p=0,004Expanded blastocyst (%)1923p=NSHatching blastocyst (%)21,820,9p=NSGood quality (%)73,884,8p=0,007Low quality (%)26,215,2p=0,01Blastocyst quality of groups 1 and 2. Open table in a new tab CONCLUSION: Blastocyst formation rate is similar in both groups, as well as the percentage of blastocysts reaching late stages on day 5. However, significantly better embryo development was given in low oxygen concentrations. Probably these results are not reflected in implantation rate because embryo selection for transfer was made according to chromosomal normalcy. OBJECTIVE: To evaluate the effect of culturing embryos from PGD cycles till day 5 of development in two different oxygen concentration conditions. DESIGN: Retrospective study of 252 PGD cycles. MATERIALS AND METHODS: A total of 937 embryos from Preimplantation Genetic Screening (PGS) cycles performed between October 2004 and October 2009 were included in the study. Cases formed two groups depending on whether embryos were cultured in atmospheric (∼ 20%) oxygen conditions (group 1 including 138 cycles), or in low (5%) oxygen concentrations (group 2 including 114 cycles). All embryos were cultured in Heracell® incubators at 37°C and 5% CO2. Biopsy of one or two cells from each good quality embryo were performed on day 3 and transfers occurred on day 5. FISH (Fluorescent In Situ Hybridization) analysis included chromosomes 13, 15, 16, 18, 21, 22, X and Y. Expanded and hatching blastocysts were graded for embryo quality considering inner cell mass and trophectoderm characteristics. Student's group t-test and chi-square analysis were used to analyze results. Blastocyst quality of groups 1 and 2. CONCLUSION: Blastocyst formation rate is similar in both groups, as well as the percentage of blastocysts reaching late stages on day 5. However, significantly better embryo development was given in low oxygen concentrations. Probably these results are not reflected in implantation rate because embryo selection for transfer was made according to chromosomal normalcy.