Miscarriage See also: Miscarriage A complete spontaneous abortion at about 6 weeks from conception, i.e. 8 weeks from LMP Some embryos do not survive through to the fetal stage, which begins about two months after fertilization (10 weeks LMP). Embryos may be aborted spontaneously or purposely. Studies using very sensitive early pregnancy tests have found that 25% of embryos are aborted by the sixth week LMP (since the woman's last menstrual period), even if a woman does not realize it.[4][5] Abortions after the sixth week LMP happen in 8% of pregnancies.[5] The risk of them is "virtually complete by the end of the embryonic period," with a rate of only two percent after 8.5 weeks LMP.[6] The most common natural cause of abortion of an embryo is chromosomal abnormality,[7] which accounts for at least 50% of sampled early pregnancy losses.[8] Advancing maternal age and a patient history of previous spontaneous abortions are the two leading risk factors.[8] [edit]Induced abortion

The majority of induced abortions occur during the embryonic period. For example, in England and Wales during 2006, 68% of them occurred by the end of the embryonic period.[9] Induced (i.e. purposeful) abortion of an embryo may be accomplished by a variety of methods, including both pharmaceutical and surgical techniques. Suction-aspiration is the most common surgical method of aborting an embryo within the United States.[10] Common reasons for purposely aborting an embryo include a desire to delay or end childbearing, concern over the interruption of work or education, issues of financial or relationship stability, perceived immaturity and health concerns.[11][12] [edit]Use in ART and diagnosis Embryos are used in various techniques of assisted reproductive technology, such as in vitro fertilization and embryo donation. They may be subject to embryo cryopreservation for later use if IVF procedures have resulted in more embryos than is currently needed. Some aspects, e.g. selective reduction, are issues in the beginning of pregnancy controversy. Prenatal diagnosis or preimplantation diagnosis involves testing embryos for diseases or conditions. [edit]Viability Current medical technology does not allow an embryo to survive outside the uterus under any circumstances, or to be transplanted from the uterus of one woman to that of another.[13] A human embryo is therefore not considered viable. [edit]Research Human embryos are being researched to determine their use in treating diseases. Their use in stem cell research, reproductive cloning, and germline engineering are currently being explored. The morality of this type of research is debated because an embryo is often used