Human Fertility
"Thou shalt not kill". Or, more broadly: Thou shalt not harm not the proper cycle of human life which rises when the unitive-procreative motive leads a man to impregnate his wife and sets peacefully in the evening of years.
The developmental mandate to move human society toward ripeness requires humans to reproduce, and the procreative tendency serves this end.
"An indissoluble link [joins] the significances of unity and of procreation ... in the conjugal act. ... An act ... which impairs the capacity to transmit life ... resists the design ... of the author of life. ... Once the generative process has begun, its direct interruption is to be absolutely rejected, [as is] any action ... that is specifically intended to prevent procreation."
Giovanni Battista Montini (later aka Pope Paul VI), Humanae Vitae (1968), 12-14.
"The weight that Humanae Vitae places on the words direct and specifically is absurd. If the intended outcome is the same, what matter how it is done?"
To such a mind, to which collateral casualties seem no better than terrorism, abstinence likewise seems no better than spermicide.
But that approach is simplistic. The idea that only results matter is as absurd as the idea that only what can be proved is worthy of belief, and for similar reasons: if I do A in order to achieve B, why should I want to achieve B? And if B is in its turn a means to the end of C, why C, and where does the chain end: what is the ultimate good sought? (More pleasure? Less pain? Both? Perhaps the pampered pet on the hearthrug is your model, or the wool-sheep in the field. A just society? You mean that the aim of your Consequentialism is a society where folk are not ... Consequentialist?)
Everywhere we encounter the incommensurable demands of spontaneous virtue (the immediate, ready-to-hand good) and of calculating utility (the remote, planned good), and neither of these rivals should be allowed to swamp the other. Virtue holds its ground, carrying its should with it.
There are exceptions. In rare emergencies, it is just to kill, abort or contraceive.
If the unborn were developed enough to have become a self, we would need to assume that it had done so, in which case abortion would be homicide, and the emergency would need to be even graver. However, my guess is that selfhood never precedes the start of the post-natal brain-growth spurt, in which case this case never occurs.
Most discussions of "late abortion" focus on physiological "viability", a different question, and irrelevant here.