I read once that a baby is like a hand grenade thrown into a marriage and I think that to a certain extent its true. You will both be under more stress and tireder than ever before so some tensions are bound to surface. IMO opinion if your relationship isn't very good a baby is only going to make it worse but if you have a good relationship then a baby will certainly alter it (things will never be the same again) but that's not nessescarily a bad thing. Since becoming parents DH and I have certainly had more arguments than we had before but we have also become much closer and work more as a team. As well as being a couple we are aslo part of a family IYKWIM.