So, basically she is edging you out on decisions?
If that is the case, you need to dig your feet in, and hold some ground. Do not let her knock you down and walk over you. But also, do not try to knock her down and walk over her. Have a frank chat with her. Let her know she needs to include you in decisions regarding the baby. Let her know this needs to be a team effort. You want to be involved in the kids life, raise the little shit, be an actual parent to it. But you can not do that if you are being ignored when it comes to the kid.
Matters of the penis? Not always. I am medically inclined (Knowledgeable of medicine and the human body in many aspects). If my future wife does not have the knowledge I have in the subjects, chances are I will be the one to take the wheel in explaining, if I had a daughter, what a period is and shit. She may be better equipped to help with tampons, relating and making her feel OK about puberty, while I'm the one who may answer any questions, as indepth as is wanted, that she may have about what is going on. It should not be one or the other. Discuss it. Try to find middle ground. There needs to be a give and take aspect to your relationship.
That is what the middle ground is for. You give on some aspects, she gives on some aspects. You both get something, you both lose something, you both are happy. Otherwise, if one person in the relationship is putting on football pads, and trying to all or nothing it, your relationship is going to fall apart. Someone is going to develop some resentment towards the other. Resentment is toxic in relationships. It bleeds into EVERY aspect of the relationship. Sexual, emotional, mental, spiritual. All of it will start to erode, until you wake up one morning, and realize you kinda fuckin hate the person next to you. May feel more like punchin em in the face than kissing em g'mornin.
But, there are some things a person may not be willing to give ground on. These are moreso what can make or break relationships. Being able to healthily handle these situations can be paramount. Find a way to get as many of these as you can, while also allowing the other to get as many as they can. Divide em up, basically. List em in order of importance.
It's difficult to say. But something usually clicks for a dad that first time they hold the baby and see em stare back at em, or maybe when they give that baby smile they manipulate ya with. The mother carries the kid, so she starts bonding with the kid once she becomes pregnant. Her body becomes it's body and it becomes personal. They feel it move, kick and have to take care of it for 9 months more than the dad does, personally with their own body. During pregnancy, the dad is more so taking care of the mom. The father doesn't get that emotional bonding like the mom does until later, usually. So ya may feel like you feel nothing about the kid. Which
Before it's born, ya may worry and fear how you'll do, you can't do this, kids gonna get fucked up majorly, etc. But once a parent actually holds that baby in their arms, looks at em, and see this, all that tends to fade out a little. Ya get your time to bond, develop an emotional attachment, possibly hitting you like a ton of bricks, maybe it takes a few weeks, but it'll happen. And you'll know what you need to do. It's yours. It's fragile, weak, and it needs you. Chances are, a switch will flip, and you will see everything completely different. The most important thing to consider, now, becomes this fragile little thing that can't do anything but seemingly annoy the shit out of you. Yet, ya will likely feel like you'd do anything for the annoying bundle of joy.
TL;DR: You have 3 months to have a frank talk about decision making, in regards to the kid, being a group activity, a discussion. To find some middle ground on shit, and everyone to participate and be included. Dads generally get that click once the kid is born and actually see it and see everything differently. So don't worry if ya still got that cold feet, almost flipping out, feelin goin.