Nope..having a kid is more random than that..just cause it comes from u doesnt mean it IS u...the sex of a baby is not guaranteed..none of that..if anything the genetics would be too close and either the baby would come out deformed or might cancel itself out and u wont even be able to get pregnant..that or u would have a miscarraige everytime u got pregnant..in order for that theory to work..the plot would have required something else other than just time travel...
Actually, the baby was deformed. Jay was born with both reproductive systems. They covered that end.
And for those racking their brains over the beginning, or 1st time the baby was born, just remember that Jay was born with both reproductive systems. By that alone, they could be implying numerous scenarios. Jay could've already been carrying Jay, ie situations like someone carrying their twin. Jay could've also birthed Jay prior to sex, in some freak sex-conceiving explanation. I know that these things were never mentioned in the movie, but they aren't unfathomable.