5 The consciousness of the same responsibility induced Us to confirm and expand the commission set up by Our predecessor Pope John XXIII, of happy memory, in March, 1963. This commission included married couples as well as many experts in the various fields pertinent to these questions. Its task was to examine views and opinions concerning married life, and especially on the correct regulation of births; and it was also to provide the teaching authority of the Church with such evidence as would enable it to give an apt reply in this matter, which not only the faithful but also the rest of the world were waiting for. (5) When the evidence of the experts had been received, as well as the opinions and advice of a considerable number of Our brethren in the episcopate—some of whom sent their views spontaneously, while others were requested by Us to do so—We were in a position to weigh with more precision all the aspects of this complex subject. Hence We are deeply grateful to all those concerned.
Source: Humanae Vitae (Vatican.va)