The pope gave an example of a woman he met who was pregnant with her eighth child after seven cesarean sections
Pope Francis has said Catholics don't have to produce children "like rabbits", instead practice "responsible parenting".
The pontiff speaking to reporters aboard his plane en route Rome from the Philippines on Monday.
He said there are plenty of church-approved ways to regulate births but most importantly, no outside institution should impose its views on regulating family size, blasting what he called the "ideological colonisation" of the developing world.
"Every people deserves to conserve its identity without being ideologically colonised," the pontiff said.
On the trip, he gave his strongest defense yet of the 1968 encyclical Humanae Vitae, which enshrined the church's opposition to artificial birth control. He warned against "insidious attacks" against the family - a reference to gay marriage proposals - echoing language often used by overwhelmingly conservative US bishops.
At the same time, however, he said it's not true that to be a good Catholic "you have to be like rabbits".
On the contrary, he said "responsible parenthood" requires that couples regulate the births of their children, as church teaching allows.
The pope gave an example of a woman he met who was pregnant with her eighth child after seven cesarean sections.
"That is an irresponsibility!" he said. The woman might argue that she should trust in God. "But God gives you methods to be responsible," he said.
He said there are many "licit" ways of regulating births that are approved by the church, an apparent reference to the Natural Family Planning method of monitoring a woman's cycle to avoid intercourse when she is ovulating.