The pope’s message was sent to participants in an international congress titled “The ‘Billings Revolution’ 70 Years Later: From Fertility Knowledge to Personalized Medicine.” The event was held in Rome April 28-29.

The Billings method is one form of what is known more generally as natural family planning or fertility awareness, a Church-approved way of regulating birth using knowledge about the couple’s natural fertile and infertile periods to either help conceive or to postpone conception through periodic abstinence.

The Catholic Church teaches in the Catechism of the Catholic Church that sterilization and artificial contraception are “morally unacceptable means” of regulating birth, while “periodic continence, that is, the methods of birth regulation based on self-observation and the use of infertile periods, is in conformity with the objective criteria of morality.”

“In a world dominated by a relativistic and trivialized view of human sexuality, serious education in this area appears increasingly necessary,” Pope Francis said, “requiring an anthropological and ethical approach in which doctrinal issues are explored without undue simplifications or inflexible conclusions.”

“In particular,” he continued, “there is a need always to keep in mind the inseparable connection between the unitive and procreative meanings of the conjugal act (cf. Paul VI, Humanae Vitae, 12).”

“When these two meanings are consciously affirmed, the generosity of love is born and strengthened in the hearts of the spouses, disposing them to welcome new life,” he said. “Lacking this, the experience of sexuality is impoverished, reduced to sensations that soon become self-referential, and its dimensions of humanity and responsibility are lost.”