Official Idol fertility rankings
Ultra mommy tier:
If you cum in these two at all, you're going to be a dad. No form of birth control works. Calendar method is useless, they ovulate 24/7. Impregnation will probably happen within the first week of trying.
Higher than average tier:
Contraception is possible, but it is still a risky move. I would recommend wearing a condom in combination with pills. Calendar method is not recommended. Impregnation is likely to happen within the first 2 months of trying.
These girls are much more typical. You can safely get away with just pills. Calendar method is reliable if done correctly. It will probably take 3-5 months of trying for a baby to succeed.
Below average tier.
These girls are much safer, although they are still capable. Pulling out is the only form of birth control you need. You're more likely to use the calendar method to try to conceive, rather than prevent, with these two. It will probably take 6 months to a year of trying before you get pregnant.
Cum inside all you want, there's nothing here. No medical treatments help either.