maybe they are making us
think that a baby donation is going to happen but maybe it is Purvi who ends up having to deliver early because of the crash. and the doctor's (not onir) will say that the baby is full term and not 6-7 months like ovi's. then maybe arjun and ovi will realize that the baby isn't onir's but arjun's. this will cause ovi to stress out and probably miscarry...as her pregnancy to begin with is weaker.
i just hope they don't make purvi give her baby up because that is too predictable (and already done in PR).
OR maybe Arjun finds out that the baby is his and he doesn't tell Ovi because she has also gone through the crash. Maybe here Arjun will tell Pruvi and Onir that they kept the truth from him about his child and now he has lost his with Ovi. The same way Purvi made him marry Ovi for Archana (a mother's) happiness, he might be spiteful and tell Purvi that she has to give him their child so Ovi can be happy (as she might not be able to conceive again.
Who knows, Arjun could be the one to force Purvi into giving her baby and here Onir really doesn't have any say as it is not his biological child.
The question will then be how the family will react to a potential baby swap. I am sure everyone will ask Onir how can he just give his baby to his brother and sister-in-law.
I feel that maybe more than Purvi, Onir will be depressed that the baby was given to Ovi and Arjun. And then maybe he can tell Purvi that the baby was his only chance of being a father as Purvi will never have a child with him because she does not see Onir like that. And then maybe that will make Purvi fall in love with Onir and see Arjun as the man who took Onir's happiness???
total speculation of thoughts running in my head.