Within Orthodox Judaism, there is a long history of divergence between what are known as 'the severe' and 'the lenient' interpretations. There is a similar range of opinions to be found in relation to 'Progressive Judaism' (sometimes also referred to as Reform or Liberal Judaism) which tries to marry the best of the past and the reality of modernity. The only thing that can be stated without contradiction is that the person who claims to hold 'the authoritative Jewish view' is deluded.
Nevertheless, some generalisations can be made. One is that Judaism regards the embryo as containing life in potential, and therefore should be treated with the utmost care and respect. At the same time, Judaism holds that the embryo does not have the same status as a human that is outside the womb.
This stance derives from a biblical incident when two men who were fighting injure a pregnant woman standing nearby: if the woman dies, they are liable to the death penalty; if just the fetus dies, then they are merely subject to a fine (Exodus, chapter 21 verses 22-23).
This relates directly to the vexed question as to when life begins. For Judaism, life does not begin fully until birth. This is reinforced by the second most important book in Jewish literature - the 'Mishnah' (compiled around the year 200) - which comments on the case of a pregnant women whose life is endangered by the fetus:
'If a woman was in life-threatening labour, the child must be killed while it is in the womb, and brought out, since the life of the mother has priority over the life of the child. But if the greater part of it had already been born, it may not be touched, since the claim of one life cannot override the claim of another life' (Oholot, chapter 7 section 6).
In this extreme example, it is emergence from the womb that marks the turning point from virtually human to fully human. This likewise is the transition in the accumulation of rights: from being largely protected to being fully protected.
Since the second century there has been much further discussion and Judaism certainly takes into account modern insights as to how the embryo develops at different stages and how it can move and feel in the womb. However, the distinction between life in potential and life in actuality remains. Thus within the overall principle of the value of life, a hierarchy of sanctity exists.
This has significant implications for research or reproducing cells for implantation because it means that terminating a fetus is not murder. It also implies that the regret at the loss involved is outweighed by benefits gained from experimentation which can help humans.
This is not to adopt a cavalier attitude to the fetus - it has to be respected and safeguarded, but in principle there can be certain situations in which its interests can be set aside.
As for the accusation that this involves 'playing God' - of course it does! Moreover, Judaism would see this as a compliment, for God has entrusted the world into our care, to better and improve using our God-given abilities. Otherwise we would never develop penicillin, carry out heart transplants or manufacture false limbs.
Other important considerations are how we approach the subject: safeguards have to be put in place so as to prevent abuse, values have to be kept before us so that arrogance does not prevail, and a sense of awe for the sanctity of life has to guide our steps so that we always enhance life and never demean it. That way we become co-partners with God in furthering the work of creation.