yacr: “The source of the Torah prohibition is subject to disagreement.
Some opinions view abortion as form of murder [retzicha], albeit one that does not carry the death penalty similar to the case of killing a tereifah where there is a transgression of lo tirtzach without its corresponding punishment. Others view abortion as falling within the prohibition of hashchatat zera (destruction of seed) in that it wastefully destroys that which could potentially blossom into life. A third view treats “abortion” as an unjustified act of chavala (“wounding”). Within this view, there are some that regard the “chavala” in terms of the mother and others that regard the prohibited chavala as being done to the fetus. A final view would prohibit abortion as being inconsistent with the affirmative obligations to protect and preserve life and well-being, an obligation derived from “lo taamod al dam rayecha” or “hashavat aveida”.
5. The halachic theory for the prohibition would determine which extenuating circumstances may amount to a proper justification, i.e., if the issur is retzicha, abortion can be sanctioned only if the fetus qualifies as a rodef. General considerations of pikuach nefesh would not suffice. At the other extremes, considerations of chavala may be set aside by lesser concerns. Hashchatat zera and hatzala can be arguably set aside for pikuach nefesh even where the fetus does not qualify as a rodef but nothing short of pikuach nefesh would suffice“
The above is a quote from an article from the same Rav Breitowitz you mentioned as a lenient source. He clearly writes that according to all opinions pikuach nefesh is necessary.