The only approved family planning method by the Church are: billings ovulation method (BOM, sometimes called incorrectly as rhythm method) and abstinence. So if one is not to run away from the consequences - pregnancy - the drill should be like this:
a) If you are and not planning on having a baby, then it's abstinence.
b) If you are planning on having a baby, use BOM to find out when the woman is LIKELY to get pregnant and during this time have sex with her. You do this with BOM so that you have sex only when she is most LIKELY to be fertile.
c) go back to a)
I don't know if that's how the RCC really formulates it but that's the only way I see it. If the RCC say that BOM can be used in order to AVOID pregnancy, then doesn't it contradict the responsibility-with-the-consequence part?
I found this article making the same point:
The RCC say that the purpose of sex should be for reproduction. It means, almost like a moral duty, that you have sex only if you want to have a child, and if you know about BOM, use it to time when to have sex. That's the highest and purest way, morally speaking. Or if man/woman are ignorant about BOM, try and try until you succeed. Otherwise, if you don't want any child, it should be strictly abstinence. That is NOT natural. "Natural" is a lottery. Men cannot tell if the woman is fertile (unlike other animals e.g., dogs and chimps) so the main rule of reproduction is to have sex as many times as possible without regard to BOM. If a Catholic doesn't want to have another child, there should not be any question to the only method allowed - abstinence. Unfortunately, the RCC also says jerking off is absolutely not allowed and that if you do it, god will know and IN FACT god is keeping a book counting how many times you jerked off. This is the reason why there are no males in heaven except a few who were run over by cars right after they had their confession.