You should capture the glow of being pregnant. It's there even if you don't feel it. Timing for a maternity session is important. We want maximum belly and minimal swelling. The perfect time is usually between 32-36 weeks.
I usually ask for my mamas to send belly pictures during their pregnancy so I can keep an eye on that baby bump. Some women show sooner than others; some women show later. I'm right there with you to help you decide when would be best.