I hate that I know this but both Monica and Chandler had infertility issues so she might not have conceived using a sperm donor anyway.
I'm remembering all kinds of things now.
Monica and Chandler had his colleague round for dinner to ask him for his sperm.
Erica, the woman whose twins Monica and Chandler adopted was ridiculed mildly for not knowing who the father was, and not knowing how you get pregnant (how she and 'Shovelly Joe' had sex would not have resulted in pregnancy).
When Chandler was working away, Monica surprised him but he was watching porn when she arrived and caught him, he changed to a shark attack programme and later she offered to 'thrash' so to replicate what she thought turned him on.
Phoebe had a surrogacy pregnancy with triplets for her brother - but his girlfriend was his ex-teacher so there was another big age difference. It always confusing me as it was Alice's eggs (with her she would they have been the best option, I think she was meant to be in her mid/late 40s) and her brother's sperm. As her half brother was estranged from her, as their father left Phoebe and Ursula as young kids, it always seemed to be a way of making a connection and becoming closer than something she genuinely wanted to do. (Phoebe tried to explore what is truly altruistic in another episode and as she got something from it sort of concluded that nothing is truly altruistic unless it harms or takes something away from you.)
The only other thing that comes to mind is Rachel having a Teeny Weeny according to a hate campaign led by Ross and Will who were both in love with her. Isn't that insulting to those with DSD conditions or just to men with small penises?
I say all this realising that it was a long time ago and applying the standards of today is unfair to the writers and those who made the programme a great success of its time.
Don't get me started on Sex in the City...