These studies were carried out to investigate the effect of culture medium free from glucose and phosphate (YS medium) on the development of the 3rd day embryos (postinsemination) to blastocyst stage and on the implantation rates and the
pregnancy
rates
in our sequential ET program. A total of 282 cycles which had more than 4 normal embryos on day 2 were analysed Embryo transfers were scheduled for on day 3 and 5 or on day 3 and 6 (sequential ET). After 2 to 3 embryos cleaved well were replaced
into
the uterus on day 3, the surplus embryos were cultured for 2 to 3 days in YS+gp medium (200 cycles) which contained 5.56mM of glucose and 1.0mM of phosphate or in YS medium (82 cycles) without them. On day 5 or day 6, 1 to 2 embryos formed
blastocyst
were additionally transferred into the uterus. The development rate of surplus embryos to the blastocyst stage in YS medium was, 50.9%, significantly higher (P<0.001) than that in YS+gp medium (36.2%). On day 5, the sequential transfer rate of
patients
with embryos developed to blastocyst stage in YS medium was 70.7%, which was significantly higher than that (36.5%) in YS+gp medium, while the sequential transfer rate in YS medium on day 6 was, 29.3%, significantly lower than that(50.5%) in
YS+gp
medium. The implantation rate and the pregnancy rate in YS group were 27.2% and 57.3%, respectively, which were also significantly higher (P<0.01) than those in YS+gp group (16.4% and 42.5% respectively).
These results demonstrate that the YS medium supports successfully the development of human embryos to the blastocyst stage, but the medium containing glucose and phosphate inhibits the development of human embryos to the blastocyst stage. We
conclude
that glucose and phosphate exerted a harmful influence upon the development of embryos to the blastocyst stage human.
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