Early pregnancy wastage: ethical considerations.

Information on early embryo wastage is relevant for debating the status of human embryos. Two main points of view confront each other. Theists hold that human embryos should be treated as human persons from the moment of conception because, even accepting that human beings are the fruit of evolution, they are part of a divine project. Without a developmental event prior to which the human embryo could not be considered a human being, embryos should be regarded as if they were human subjects. After all, if one believes in the resurrection of the dead, it makes no difference at what stage one's life ends. Secularists oppose the idea of granting absolute value to human life from its beginning because early human embryos lack individuality and sentience. Personifying embryos is morally absurd because it would mean that countless human beings never had even the slightest chance to express their potential and, in the light of this catastrophic loss, one would expect early pregnancy wastage to have become an important research priority; this is not the case. In practical terms, most Western countries have legalized first-trimester abortion, de facto giving embryos a lower status than that of full person.

Fate of fertilized human oocytes.

Establishing the proportion of fertilized oocytes and early human embryos that proceed to term may help policy makers in their evaluation of when the life of a new human individual begins and in determining the nature of protection to be accorded to it. The rate of spontaneous abortions, although increasing with age, overall does not exceed 15%. However, abortion rates refer only to 'clinical pregnancy', whereas early embryonic loss is more common than generally believed. Evidence of such wastage comes from many sources. Human fecundity rarely exceeds 35% and may be decreasing due to deterioration in semen quality. Embryological studies show that 50% of randomly recovered preimplantation embryos have severe anomalies. The study of sensitive markers of pregnancy, such as human chorionic gonadotrophin, indicates early embryo wastage in the order of 50%. Pregnancy wastage may be a function of the time lapse between ovulation and implantation as the implantation window extends between menstrual cycle days 20 and 24. Finally, data obtained with natural IVF cycles also indicate major losses, with an overall pregnancy rate of 7.2% per cycle and 15.8% per transfer. These data, however, are biased by a high cancellation rate and low oocyte retrieval in natural IVF cycles.