Thank you all for your answers and your feedback (and your courtesy) in relation to this question, it is a subject that has intrigued me for a while, I wanted to know if it was quite common or not, to be honest it's not something I would do (I'm not into the cuckold fantasy at all), but I'm very admiring those who make this (voluntary) choice, I wish the best for these couples.
The risk of having a baby always exists, especially when you fuck without a condom (personally it's my case, I hate condoms) A friend of mine (from Sweden) fucks with her black boyfriend bareback and told me that if he got her pregnant, she would keep the baby without hesitation.
Anyway, I don't know if all these feedbacks are real or just fantasies (lots of trolls on this forum, but don't feel targeted by this comment if you're not one), but thank you everyone.