That’s the point… “any child
conceived was supposed to be brought into this world.” With the case of the nuns, the act that would have possibly resulted in a pregnancy was rape, not marital intercourse, and the contraception would have prevented (supposedly) any pregnancy. There would have been no child to consider. This was an extraordinary circumstance, to be sure, but the question of abortion didn’t enter into this. (I have no idea what became of those brave nuns, or have long since forgotten.)
The Church allows natural methods of spacing of births achieved through periodic abstinence (NFP), but in the case of Accutane, there is no “safe” period while you’re on the medication. Therefore, abstinence would be required. (Is there really nothing else you can use? I believe Accutane has actually been banned in the US. It can have long-term side effects.)
I haven’t seen the full transcript of what the Pope said with regard to contraception and Zika, so I won’t speculate, except to guess that the press hasn’t got it right.