Having now done both, I can speak from experience when I say that growing and giving a birth to a baby is actually a lot like running a marathon. When you're running you always have the choice to quit; with a baby once you get going it's pretty much no way out but through. But while those things require slightly different flavors of mental and physical toughness, the underlying degree of effort is quite similar.
And, just as you wouldn't run a marathon without a few photos to document your accomplishment, I think a few belly photos here and there are most necessary.
Here are three ideas that make fun photos and are easy to shoot even if you don't consider yourself a "photographer".
1. The Silhouette
I found this idea on White House Black Shutters. She did hers completely by herself with an iphone--all you need is a camera app with a self-timer and a minimal processing app. (Full disclosure, I used my SLR, but only because it seemed silly to spend a few bucks on a timer app when I already had the tools I needed. You really can do this if all you have is an iphone.)
I propped my camera on my dresser, put on some form fitting clothes, and set the self-timer. It took me several tries to get myself lined up exactly right, but I love the result. It's not quite the boudoir-esque maternity photos you can find on Pinterest--which are often lovely, just not me--but it's still sorta captures the voluptuousness of things.
2. Fruits and Vegetables
For several months, we've been using this paper pregnancy countdown chain to help the Kid understand how big the baby is and how soon she'll be here. It's been fun to compare to that--and learn about some exotic fruits and vegetables along the way--but I think going the seasonal route requires less valuable brain energy--i.e., with no planning beforehand you can just say, "Hey, Sweet Husband, look! Our Halloween pumpkin is as round as the baby. Here, snap a picture!"
If you're going to go this route, save yourself some math later and tag the photos with how far along you are as you take them. I can't tell you how many times I've looked at just the date on pictures of my first pregnancy and had to pull out my fingers and toes to figure out, "Now how far along would I have been then?"
3. The Belly Decorating Party
One of the trade-offs of having a baby in a less medicalized setting (that's code for home or birth center) is that you have to make it to 37 weeks. For the health of baby, if you go into labor before that it's off to the hospital, missy!
As such, with both kiddos now (just hit the milestone with Little Miss this past weekend) we've had a little celebratory belly decorating party at 37 weeks. Lot's of people go get beautiful henna work done, but--again, saving some brain effort--we've just had fun doodling with Crayolas. (Here's the Kid, in all his doodled glory.)
Once your belly is decorated, get everyone's hands on it, hold your camera up above your head, and take some shots down. It's totally goofy-fun, but, at the same time, I like how if captures the whole family effort it takes to grow a nice big baby belly.