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Cleavage rates

By: Bert Stewart, Fertility Associates, Auckland
03 July 2002


Question:
	Are my embryos going too fast, or just right? I believe it is fairly standard practice to select embryos for replacement by their cleavage rates amongst other things. Here in Auckland we first separate out the cleaved from non cleaved around 25 hours post insemination, a quick look at around 45h then they are further selected into 8-cell vs. < 8-cell at around 65h post insem. The problem is that we are often seeing 6 or more cells at 45h, and 12 or more at 65h. Are they 'abnormally' fast, so to be selected against, or just the ones that we should be replacing? I can't believe that so many 'abnormals' have only relatively recently appeared in such numbers. My unease relates to seeing (many years ago so I can't quote a reference) in vitro human embryo cleavage rates with upper and lower thresholds for normal. I suspect that these rates were established using very basic culture conditions, and with modern media and optimised culture conditions, embryos are expending less energy maintaining their integrity and more on getting on with the job of cleaving. So, what are the upper and lower thesholds from my modern culture system? PS system used is, Vitrolife G-media, embryos cultured in 40?l drops under oil. Culture in MINC 1000 incubator at 37C, 6% CO2, 5% O2, 89%N2