It appears that for some women and families the prime obligation is to apply the principle of 'Responsible Parenthood'. 
As even Humanae Vitae advises.

God's reqirement for practicing the virtue of Prudence, in their judgment, seems to place the decision to terminate a pregnancy into human hands. They might see it in context of miscarriages. We tend to forget that not every pregancy is, by nature, meant to be carried to term.