From the above encyclical:
10. With regard to the biological processes, responsible parenthood means an awareness of, and respect for, their proper functions. In the procreative faculty the human mind discerns biological laws that apply to the human person.
With regard to man's innate drives and emotions, responsible parenthood means that man's reason and will must exert control over them.
With regard to physical, economic, psychological and social conditions, responsible parenthood is exercised by those who prudently and generously decide to have more children, and by those who, for serious reasons and with due respect to moral precepts, decide not to have additional children for either a certain or an indefinite period of time.
However, IMHO, there is still a problem with the Pope's words as reported. Specifically, his use of the disparaging phrase "like rabbits" as well as his off-hand, derisory reference to the pregnant lady with seven children. Sadly, +Francis' words reinforce the popular pejorative stereotype of Catholics who heroically follow Church teaching and do not use artificial contraception.
He could have made the point in a far more charitable, concise and less bombastic manner. However, as is by now routine, whenever a microphone is placed in front of him and a captive audience beckons, the sound of his own voice appears to be self-intoxicating.