What do Jews believe about conception?

Answer 1

If you are asking if Judaism teaches that life starts at conception, the answer is no. All streams of Judaism teach that a fetus is at most a potential life and doesn't become a full life until it is able to survive independent of the womb as per the Tanach (Jewish Bible).

The significance of the concept of "potential life" is that the Tanach clearly specifies that a whole life takes precedence over a potential life and that in situations where the life of the mother is threatened by the fetus, abortion is a requirement. The only difference in the various streams of Judaism is what they consider what qualifies as a threat to the mother's life. In Orthodox Judaism, the threat must be a direct physical health threat while most other streams consider any threat both physical and mental.

Answer

The basic principle of Judaism is that "what is hateful to you, do not unto your neighbor"; Judaism is a religion that emphasizes Life, even going so far as to contrast the alternatives such as sacrifices to Molech; In a modern world whose tendency to regard innocent unborn children as 'mortal threats' is overbearing, it behooves us to recognize the modern version of Molech for what it is. The insensitive language - sometimes even seeming as though they leap at every opportunity of adding horrible words to every discussion - of those who have insufficient respect for the Life of the unborn child identifies them clearly.

Hence the Ultra-Orthodox at least, have strong preferences in favor of the sanctity of all Life, even potential Life, from the moment of conjugal union; even before that, given that it is a mitzvah to try to have children.

Jewish people have the duty to behave in a way that leads to conception, in marriage; then to do their utmost to try to guarantee the health / safety of the child without limit as to time; although the imperative is stronger for a man, at least until he's had 2-3 children already. A woman, for instance, is entitled to refuse all marital activity as childbirth is inherently hazardous, although she'll be divorced at her own cost PDQ for that!

The opinion cited originally, while it largely represents the author's interpretation of mainstream writing, contains some overstatement as written; 'the answer is' / 'all streams' is definitely overstatement in view of the fact that the Haredi stance clearly differs; while 'is a requirement' is a matter of debate, in fact many say it should read 'is a possibility', even when referring to far less harmful procedures; the relevant tractate is 'the Beraita of the 3 women' that leaves the question open although tends to support the 'is a possibility' interpretation; see, for more, related link 'Jewish Doctrine of Contraception'