For now at least, the pregnancy will work like this, you have the option to get her pregnant like you said, if you decide to do so, you get her pregnant for 9 months (related to story, not skipping days) after which the child is born. If you turn her down, then you can’t get her pregnant anymore, at least not for now.
Much later in the story, I might add the option to get her pregnant again or for the first time, but nothing is set yet.
Edit: Also, while pregnancy is connected to the story, it is still optional