Watch for her to build a big nest, rest more, eat less and do a lot of butt end licking. That's usually the signs that delivery is very close. Sometimes you'll even see the "dead rat" pose where a female will lay flat out on her back and you swear she's kicked the bucket on you. I guess it relieves pressure on their big swollen belly but it sure gives you a shock when you first see one of them sprawled over like that.