I'm having the "Oh my goodness how can it be only 4 months from now?" feelings. I guess having 2 children already, I can definitely imagine labour and tiny baby, but so soon? that's the part that seems crazy to me, even though I feel like the past 4 months have also been pretty long I feel like December snuck past, and now suddenly I have a ton of stuff to do, and very little time to do it in - both at home and at work!
As for babies and heads and whatnot, this is my way-too-long op-ed view on things...
I think it's very important to visualize that your body can do this. It has a way to do this, and for me, part of that visualization is founded on accepting that baby-heads do, indeed, fit through seemingly tiny spaces, and I try not to get caught up in the detailed mechanics of how all that happens. Some people love to know every last detail - but I prefer to accept that yup, that head came out through there, without necessarily imagining the stretching and shifting that occurs to make that happen. I liked being present, and feeling my body doing amazing and powerful (and yeah, sorta painful) things, but at the same time, when I visualize my next birth, it's more as a series of changes and phases - not so much a vision of that head coming out of your body. And now that it's January, I guess it's time to start thinking a bit about that next birth!
In preparation for a first birth, I would focus far more on getting to the point where you are going into transition to pushing, than I would on the actual pushing. Some people have a great deal of trouble at the pushing part, but in my experience, the strength you need, and the support you need, is a lot about the lead up - the active labour before transition - especially with your first child. I went in to my first birth thinking that pushing and heads and babies coming out was what labour was all about, but it's a far longer and deeper process than that, and I think that it is easy to be overwhelmed (and have a maybe less than stellar outcome) if you focus on the birth itself and not the process to get to birthing. This is just totally my opinion
With my first, I had this idea that I was a fit and fabulously capable person and at 40 weeks a little timer would go off in my body and zing, in about 8 hours I would pop out a baby...fast forward to week 43, when I was induced at 43+2, and, well, I laboured for about 48 hours with induced contractions (hard and constant - with the also constant threat of a C-section if I became too exhausted) and dilated from 3-10 cm only about 6 hours before the baby was born. I never expected that, and certainly had not prepared for birth to be hard for me - totally a ridiculous stance to take in hindsight, but my flawed reasoning was that I have a high pain threshold and most athletic things are easy for me, the whole labour thing seemed like a bit of an athletic event, so how bad could it be? Oh how I laugh now.
The most humbling and amazing part of birth for me is how hard labour can be, coupled with how you can handle that. If I was going into my first birth again, I would spend a lot more time preparing my mind for not having control over how long I might be contracting for, and for how tired I became. The pushing, with both my births, was sort of an end game - it was a done deal once you get to push (I know this is a huge generalization and not every woman will have that experience). But I will never forget the amazing revelation of what a source of birth support my partner was during the phase of labour prior to transition, or learning about the unknown reserves of my own strength and power from those tough two days. My second birth was only about 8 hours with no intervention or pain meds, and it was a totally different and great (not fun, but great) experience too (sort of more the birth I expected with the first). Again, the active labour to get to transition was for me, far more physically and mentally tough than once I got to push.