My illegal girlfriend is pregnant with my child (that will not be determined until after the child is born an a DNA test given). If DNA testing proves this child is mine can I gain full custody so she can never leave the country with my child ? Thanking you in advance

You can not gain custody just because she is illegal, you will have to prove she is an unfit mother just like anyone else can. Plus even a citizen could always leave the country if they wanted to.

Also the child is born within the US, will be a citizen which will help the mother get legal staus a little easier.

But she can get custody, and force you to pay child support if she does not leave the country also.

Your other question was almost exactly the same it has been deleted. To answer the one issue in it, you can report her, guess her being illegal when you sleep with her was OK, But most likely she will still have custody of the child, just being illegal does not take away her rights or make her a unfit mother. And she can still use the US courts to make you pay child support, ( bet that money goes a lot further in her country)