Robert: Should we do more research on natural embryonic death — its incidence, causes, and prevention? Very likely the answer is yes. But recognition that human embryos have a right to life does not lead simply and as a matter of logic to a moral obligation to undertake any particular research program. How much the program would cost and whether it would have much prospect of success would have to be considered before embarking on it. (We spend research money on reducing the mortality of 95-year-olds, but there are limits to how much we spend and how urgently we seek answers, and those limits are not based on any disbelief in their right to life.)
The fact that pro-lifers have not embarked on this course implies neither that human embryos lack a right to life nor that pro-lifers agree that they lack it. Leaving aside morally relevant questions of feasibility, most pro-lifers (like most people generally) do not know very much about the issue. And we are more focused on fighting greater evils, such as the conferral of the status of a constitutional right to the act of deliberately killing a human being.
Finally, I note again that none of this hypothesizing about drugs to prevent natural embryonic death, and so forth, has gotten us any closer to an argument that human embryos are something other than living human organisms or that the deliberate killing of some such organisms is a matter of moral indifference.