You mean non-muslim, monogamic marriages?
This was actually in my 1st game of CKII, initial wife was in her late twenties and died like 5 years into the game. Then I got my king a young wife (he was in his late 30s) and hit the motherlode because they had a large offspring togheter, but eventually an epidemic killed her. Then I figured I had enough kids so I went for an olde wife with titles and no heirs (older than the 16-years old I previously got I mean). Now, at this point I didnt know you can have children even if youre not in e same court, so I felt cheated when my wife staid at her original court despite the marriage...so I did the only reasonsble thing and edited the save file to give her pneumonia... Yeah. After that I got another wife, if I recall the elder daughter of the french king, but besides like a child or 2 nothing came out of it and she died at some point. By then my king was in his late 70s and I married him to an orthodox princess... Not sure what culture, but she wasnt white... Anyway I guessed she nursed him till he died at which point I married her back to her homeland cause why not.
On an unrelated note, all the sons of this king married into and extinguished the Salian house, as the Kaiser had the worst round of luck Ive ever seen and had 5 (five!) daughters and no son, making my nest queen the absurdely unlikely heir of Franconia. Also the day the Kaiser died the HRE collapsed completely, not sure if the no male heir thing had anything to do with it, but it sure was a good first campaign.