
it is mentioned by the father when ci nian was watching behind the bushes when he got out of jail.. and later on when he was talking with lua mao his room mate when he was telling to tell cheng who is the real father.. but ci nian dont want to say anything because his father talked about him like a monster and he thinks of him self like that too, so he think that cheng will leave him if he finds out

I've read the whole novel and it was very clear that CN knew he could get pregnant ever since. He even tried to avoid getting a full on check-up in a hospital because ever since he was a kid, he was only treated by the Xu's family doctor so they could conceal his body. And one of his rules with Dong Feng was to always wear protection, though DF didn't know that CN can get pregnant, he followed his wishes which was why CN didn't have unplanned pregnancies.
Guys pls help (T_____T) how did they get pregnant??? Who's the mother??? Who's the father?????? Im still at chp 9th