I haven't heard of any other method besides noticing the big belly.
---------------------------------- BP owner since Oct 2008, so yeah, I'm no expert.
0.1.0 pastel bp
1.0.0 spider bp
0.1.0 albino bp
1.0.0 bumblebee bp
1.0.0 yellowbelly bp
0.0.1 normal bp
1.0.0 normal western hognose
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, chocolate in one hand, body thoroughly used up, totally worn out and screaming "WOO HOO what a ride!"
And if they're REALLY pregnant, either with a lot of babies or soon to pop (or both), you may see this. This girl had 19 babies about 12 hours later. However, even when she had less than 8, I could see some movement. Not like that, but still noticeable.
Expectant mothers will start cleaning the area where the nipples are to make them more easily accessable for the pinks. Also they will really get a pear shape (large belly) to them when they are close to dropping their litter.