Man, just be there. Try to avoid the arguments as much as you can. Words can not be taken back, so avoid saying things you don't mean (easier said than done, I will admit, but it can be done).
She's hormonal, and after the baby comes she will be very tired. I can't remember the percentage, but a huge amount of parents break up in the first 18 months of a first childs life.
'People are never perfect but love can be. People waste time looking for the perfect lover rather than creating the perfect love' - Princess Leigh-Cheri from Still Life With Woodpecker.