Research published in Human Reproduction**,Europe’s leading journal of reproductive medicine, has shown that, in mice, stimulating the ovaries by hormone drugs to produce more eggs appears to impair both the development of the embryo and its likelihood of implanting in the uterus.
Dr Gudvor Ertzeid and Dr Ritsa Storeng from The National Hospital, University of Oslo, Norway, undertook the study to establish whether impaired embryo quality or changes in the environment in the uterus could be responsible for the observed adverse effects of superovulation on implantation and fetal development in mice.
They used four groups to evaluate the impact of ovarian stimulation on embryo quality and uterine receptivity:
* embryos from control donors to control foster mothers
* embryos from superovulated donors to control foster mothers
* embryos from control donors to superovulated foster mothers
* embryos from superovulated donors to superovulated foster mothers
They found an adverse effect of superovulation on embryo quality. Only 12% of embryos from superovulated mice implanted in control foster mothers compared with 25% from control donors. An adverse effect on implantation was observed. Only 7% of control embryos implanted in superovulated foster mothers compared with 25% in control foster mothers. Further fetal development was also impaired as nearly twice as many implanted embryos died in superovulated foster mothers as in control foster mothers (69% against 36%). The mean weight of live fetuses from superovulated foster mothers was also lower than that of those from control foster mothers.
Dr Ertzeid said: "We don’t yet know why superovulation damages embryo development or the conditions in the uterus. It may be an effect of the hormonal drugs on the chromosomes in the embryo and indirectly on the lining of the uterus. That is still a question for research. In general, it is not possible to extrapolate from animal models to humans. However, considerable similarities exist among many mammalian species in the early stages of development which suggests that information obtained from laboratory animals at the time around the implantation of the fetus might also be applicable to humans."
European Society for Human Reproduction and Embryology. January 2001