We’re nearing the end of Part Two Chapter One in the Pastoral Constitution on the Church in the Modern World and its reflection on marriage and family in the modern world.
In article 51, we look at the need to be open to children and to safeguard human life from the moment of conception. This is Humanae Vitae in seed form.
Here is the footnote, which also alludes to what will eventually be Humane Vitae:
14. Cf. Pius XI, encyclical letter Casti Connubii: AAS 22 (1930): Denz.-Schoen. 3716-3718, Pius XII, Allocutio Conventui Unionis Italicae inter Obstetrices, Oct. 29, 1951: AAS 43 (1951), pp. 835-854, Paul VI, Address to a group of cardinals, June 23 1964: AAS 56 (1964), pp. 581-589. Certain questions which need further and more careful investigation have been handed over, at the command of the Supreme Pontiff, to a commission for the study of population, family, and births, in order that, after it fulfills its function, the Supreme Pontiff may pass judgment. With the doctrine of the magisterium in this state, this holy synod does not intend to propose immediately concrete solutions.