Improved blastocyst formation with reduced culture volume: comparison of three different culture conditions on 1128 sibling human zygotes

Abstract

Purpose The aim of the present randomized, comparative study was to evaluate the effect of reduced culture volumes on sibling human embryo development. Methods Firstly, sibling injected oocytes obtained from 88 out of 165 consenting couples undergoing infertility treatment were cultured either in large (35 μl) or in small drops (15 μl) of culture medium. Secondly, sibling injected oocytes from 77 couples were cultured either in large (35 μl) or in mini drops (7 μl). Embryo quality on day-2 and day-3 and blastocyst formation rate on day-5 were evaluated. Results No statistically significant difference in terms of embryo quality was detected comparing embryos cultured either in large (35 μl) or small (15 μl) drops until blastocyst stage. Similarly, no difference appeared between large (35 μl) or mini (7 μl) drops until day-3, however a significantly higher blastocyst formation rate was observed in mini (7 μl) drops on day-5. Conclusions Reduced culture volume seems not to influence early embryo development but a reduction of medium appears to positively affect blastocyst development. This supports the hypothesis that the pre-implantation embryo produces autocrine factors which exert a positive effect on embryo development when culture is performed in a reduced volume.

Reduced blastocyst formation in reduced culture volume

“…These data are in contrast with those of Minasi et al [10], which may be related to the difference in culture media (Origio in the present study versus Sage by Minasi et al). The two culture media have a different amino acid constitution and concentration and were supplemented with different protein sources.…”

“…The recent report by Minasi et al [10] comparing embryo culture in either 35 or 7 μl droplets reported comparable embryo quality on day 3 (∼80 %), but significantly higher blastulation rates on day 5 when embryos were cultured in 7 μl droplets (50.5 versus 70.0 %, p<0.05). It should be noted that the authors did not present data on cell number on day 3 nor on expansion stage and blastocyst quality on day 5.…”

“…A recent report by Minasi et al [10] concluded that a reduction in culture volume from 35 to 7 μl is associated with a significantly higher blastulation rate on day 5. In order to confirm these results, we designed a prospective sibling study in which injected oocytes were cultured individually in either 25 or 7 μl droplets until day 5 or 6 after oocyte retrieval.…”

“…Despite the long history of IVF, the best culture system is yet to be elected and the majority of the labs use different methods to culture their embryos. At present, three major embryo culture systems are used: (i) grouped culture, with three to five human zygotes/embryos cultured together [22,5,12,13], (ii) individual culture, where every embryo is cultured in an individual droplet [22,10,12], and (iii) individual culture with medium exchange between embryo droplets, where although the embryos are cultured individually, the presence of small communicating orifices in the walls allow the passage of medium [5]. Besides the culture system, the choice of the culture medium is also important and may be either: (i) single media, in which the zygote/embryo is cultured from day 0/1 until day 5 or (ii) sequential media, composed of both a cleavage and a blastocyst medium, in which a consecutive medium change is performed on day 3 of embryo development.…”

“…Besides the culture system, the choice of the culture medium is also important and may be either: (i) single media, in which the zygote/embryo is cultured from day 0/1 until day 5 or (ii) sequential media, composed of both a cleavage and a blastocyst medium, in which a consecutive medium change is performed on day 3 of embryo development. Finally, different culture volumes can be applied for every culture system and culture medium [22,5,10]. Any selection of the abovementioned parameters should account for an optimal balance between the need to limit the concentration of toxic metabolic molecules, such as ammonium, and the positive effects of the beneficial autocrine factors on embryo development [21].…”