In that species gravid females are oretty easy to identify. There translusent skin will allow you to see the developing babies. I've posted a picture of one of my gravid females. The babies are very easy to see in her. The picture isn't tyhe best but you can see them on the side.
Johns right. You'll know. When you look at the sides as she gets bigger you'll see little white round objects in there. If you look close enough you'll make out the babies threw the skin. It's very cool to see btw. Third picture looks like there might be something going on in there but that to clear. It very well could be lighting, the position she is in, or me seeing things since I don't have my glasses on. She'll get rolly polly fat and you'll be able to spot the babies threw the skin.