The human preimplantation embryo can be defined as the developing organism from the time of fertilization to approximately the fourteenth day after fertilization, assuming a normal rate of development. The major preimplantation stages in human and other mammalian embryos are usually distinguished by such names as zygote, morula, and blastocyst. By the end of fourteen days the early human embryo has, except in rare cases, lost the capacity to divide into two individuals; it has also begun to exhibit a longitudinal axis that forms the template for the spinal column, an axis called the primitive streak (McLaren; Dawson, 1990a).
Preimplantation embryo research generally requires the associated procedure of IVF (although it would in principle be possible to retrieve an early embryo by flushing it from the uterus of a woman following in vivo fertilization of an ovum). Thus the question of research on preimplantation embryos did not arise until IVF techniques had been developed and validated, first in laboratory animals, then in humans. In 1959 M. C. Chang of the Worcester Foundation in Massachusetts was the first scientist to demonstrate unambiguously the fertilization of nonhuman mammalian oocytes in vitro. Chang's success was followed in 1969 by the first confirmed report of IVF with human gametes by three British researchers (Edwards et al.). Only nine years later the first human birth after IVF—the infant's name was Louise Brown—was reported by members of the same British research team (Steptoe and Edwards).
Given that IVF is required for preimplantation embryo research, the risks to the woman of ovarian stimulation and oocyte retrieval are relevant to the discussion. Ovarian stimulation with injectable gonadotropins has been associated in some studies with an increased risk of ovarian tumors (Harris et al.), though the association is controversial. In addition gonadotropins are associated with a risk of ovarian hyperstimulation syndrome, which is associated with ovarian enlargement, massive fluid and electrolyte imbalances, renal insufficiency, and in rare cases thromoembolism and death.
There are two major contexts for research on preimplantation embryos. The first is one in which the transfer of the embryo into the uterus of a woman (or perhaps, in the future, into a device that can support full-term fetal development) is planned. In the second context, no embryo transfer is envisioned and, accordingly, the death of the embryo or later fetus at a stage before viability is intended. These two research contexts raise somewhat different ethical issues.
RESEARCH FOLLOWED BY EMBRYO TRANSFER. In the years preceding the birth of Louise Brown in 1978, researchers devoted substantial attention to improving the prospects for successful IVF and embryo transfer. This research focused on methods for maturing oocytes, facilitating fertilization, and culturing or cryopreserving early embryos (Biggers). During the 1990s, researchers continued this type of research. New methods for assisting fertilization have been devised, including the drilling of a small hole in the outer shell of an oocyte or the injection of a sperm directly into an oocyte, a process known as intracytoplasmic sperm injection (ICSI) (Van Steirteghem). Similarly researchers have developed methods for removing one or two cells from an eight-or sixteen-cell embryo in order to perform preimplantation diagnosis of genetic or chromosomal abnormalities (Edwards, 1993). These techniques are performed so that only embryos without genetic abnormalities are transferred to the uterus, while affected embryos are discarded. In the twenty-first century, one can anticipate research that attempts to prevent the later development of a genetic disease (for example, cystic fibrosis) by treating an individual at the embryonic stage of life. If successful this kind of disease prevention by means of gene modification would be likely to affect all of the cells of the person, including his or her reproductive cells (Wivel and Walters).
The ethical issues that arise with preimplantation embryo research when embryo transfer is planned are at least analogous to those that arise with fetal research in anticipation of birth, with research on infants, and with research on children. That is, one attempts to perform a careful analysis of the probable benefits and harms of the research to the individual and to others; one seeks an appropriate decision maker, usually a genetic parent or a guardian, who can represent the best interests of the potential research subject; and one looks for a disinterested mechanism for prior ethical review of the proposed research. This kind of embryo research, in which the research procedures are often designated therapeutic or beneficial, is generally approved by commentators on the ethics of such research, even if they diverge widely in their attitudes toward IVF, the moral status of preimplantation embryos, and abortion (see, e.g., Ramsey, 1970; Catholic Church; Singer et al.).
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