huh??

you know egg donors, they've used feng's sperm and an egg donor to have rourou, i don't know the details with the scientists and why yi yun doesn't have a baby with his sperm but yi yun was the guy who looked after the egg donor throughout the pregnancy and rourou up until now

i think jinyao revealed that he actually exchanged his sperm and yiyi's when rourou was made. Jinyao was safeguarding yiyi's sperm but something came up and he kinda lost it (he hasn't told yiyi yet) But based on the subsequent scenes, *may be spoilers be warned*
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it appears that the aunt was the one who 'stole' the sperm jinyao was keeping, thinking that it was still jinyao's sperm

hope i made sense witj all this sperm talk anakakskoqns

so it's yiyi's baby since it actually got switched?

and why tf is jinyao protecting yiyi's sperm? did he know yiyi before??

No no, it's like this. Jinyao needed to secure an heir but didn't want his family to know. So he went to the same facility as the one yiyi went to, and exchanged sperms so that you would bring up Jinyao's baby( without Feng family knowing) thinking it was his baby. He was a selfish bastard ngl. Jinyao was going to throw away yiyi's sperm but changed hearts and he kept it in a "safe" lock. But Jinyao's"good" aunt came to know about the whole sperm thing ( she thinks it's Jinyaos) so she stole it, fertilized, and surrogated it. Most probably because she considers Jinyao a weak heir and wants a contender for the Feng group.
Hope this made sense ^_^

*yiyi would bring up Jinyao's baby
(In the fourth line)

so that baby just now (the baby the aunt was holding) was that yiyi's or was that irrelevant to this?

Yes it's yiyi's AAAAAA MORE BABIES IN THE FENG-YI FAMILY

That's probably yiyi's

I thought she was the nicest of them. Why did she steal it ?

i dont remember that well why but she stole it bc it was registered as fengs sperm not yiyi, only feng and his close people knew he exchanged (bc he didnt know his family to know he already had a son) so now the auntie found out and decided to use it. reaaaly high chances she has bad intentions, no one steals and uses sperms of nephews out of nowhere, specially if theyre heirs