Gonadotrophin stimulation of donor females decreases post-implantation viability of cultured one-cell hamster embryos

Hamster one-cell embryos were collected from two groups of donors: females that were super-stimulated with pregnant mare's serum gonadotrophin (PMSG) and females that were not. Embryos were cultured for 72 h and scored for development. Morulae and blastocysts from the PMSG- and non-stimulated females were transferred into contralateral uterine horns of non-stimulated recipient females, so that experimental embryos (from PMSG-stimulated females) and control embryos (from non-stimulated females) were paired within a single recipient. Right and left uterine horns of recipient females were examined 11 days later for the number of implantation sites and fetuses. After 72 h of culture, development to morulae and blastocysts was not significantly different for embryos from PMSG- and non-stimulated females. However, embryos from PMSG-stimulated females compared to controls had significantly reduced mean cell numbers (18 versus 21; P=0.003) and a two-fold decrease in viability post-transfer (20 versus 45%; P=0.02). These findings indicate that gonadotrophin stimulation compromises subsequent developmental competence either during oocyte maturation or in the very early embryo, but it is unclear whether reduced viability is a direct effect or is an indirect consequence of PMSG stimulation.