The development of fertilized human ova to the blastocyst stage in KSOM AA medium: is a two-step protocol necessary?

Abstract

Current protocols for the culture of human zygotes to blastocysts use two-step sequential media systems. The efficacy of a one-step system involving potassium simplex optimized medium (KSOM AA) has been investigated. In study 1, development of zygotes from days 1 to 3 in KSOM AA was compared with that for medium P-1. In study 2, embryos were cultured from days 1 to 3 in P-1 followed by culture from days 3 to 5 either in KSOM AA or medium CCM. In study 3, the ability of KSOM AA to support development of embryos from days 1 to 5, without medium renewal, was compared with the sequential media system P-1→CCM. The cell numbers and fragmentation scores of day 3 embryos were distributed similarly following culture in KSOM AA or P-1. Significantly more KSOM AA embryos exhibited cytoplasmic pitting. Blastocyst formation rates were not significantly different whether embryos were cultured in the P-1→KSOM AA or the P-1→CCM systems, or when cultured from days 1 to 5 in KSOM AA without medium renewal or in P-1→CCM. Five babies have been born from nine blastocysts transferred after extended culture in KSOM AA. A one-step protocol involving KSOM AA can be used successfully to culture human zygotes to the blastocyst stage.