Speaking to journalists on his flight back from the Philippines, the pope said that he once asked a mother of seven children who was pregnant with her eighth if she wanted to "leave behind seven young orphans".
"She said, 'I trust in God.' But God gave us the means to be responsible," the pope said. "Some think, and excuse the term, that to be good Catholics, they must be like rabbits."
Following the church's teachings did not mean "Christians should have children one after the other", he said.
His comments came at the end of a trip to the Philippines, the Catholic Church's Asian stronghold, which last year passed a family planning law after a 15-year battle by the Church to block state-sanctioned contraception.
The law allows the government to begin distributing free contraceptives to millions of poor Filipinos.