The category "avoiding pregnancy" as applied to a nun could only and ever be under the form - ironic as it may be - of taking a pill that prevents ovulation in the case of the very real threat of being raped. For again, she is not in conjugal relations with a spouse. And her celibacy is not about avoiding pregnancy; not becoming pregnant is merely accidental to it. The category "avoiding pregnancy" as applied to married couples can only and ever be legitimately applied under the form that is termed Natural Family Planning in the case of certain contexts and circumstances.
In other words, a huge implication of Pope Francis's statement is that NFP is not in and of itself a good. For he said that "avoiding pregnancy", in contradistinction to the intrinsic evil of abortion, is not an absolute evil. Which is also to say that it is not good all of the time, or even some of the time, or even when it is lawful.
If avoiding pregnancy is termed as not necessarily an absolute evil, then it can be an evil. Indeed, it is an evil if a couple avoids pregnancy because they just don't want children when they have the means, or only want so many, or want instead to accumulate mammon, either indefinitely or for a planned period of time. This would include Natural Family Planning, the rhythm method: if it is used for the above reasons, then you are contracepting, which is an evil, according to the teaching of the Catholic Church.
Pope Francis was upholding solid Catholic teaching against the neo-Catholic belief that NFP is good no matter what.
He was also reiterating a previous statement he made about a mother who needed to avoid pregnancy, under his own admonishment, so as not to deprive her existing children of a mother. He stated that some Catholics mistakenly think that they need to breed like rabbits.
"Planned Parenthood does wonderful things, but not as it relates to abortion." --Donald Trump