When Pervy was expecting she also got clingy right before it was time. I think they also get scared and nervous. It's nature but something big is about to happen to them and they seem to sense it. Especially the first time.
I haven't read all the replies so if someone already said this then forgive me. When I was growing up (before spay & nueter education) and we had cats I remember one of our mama kitties would scream her head off when she was in labor! It was so sad and it scared me to death!! She was fine and had beautiful healthy babies. Pervy never made a sound but you could see her pushing and the pain in her eyes broke my heart.
The only reason I'm telling you all this is to prepare you. It could be sad to watch her hurting but just know that if your there and you stay calm then so will she. I hope you can be with her because it is a wonderful bond when you share it with them. It's kind of like being birthing coach!! It's also cool to just come home and find it over with!!! You didn't have to stress that way
Can't wait for the new babies. It's like we are all standing around the nursery window just waiting!!!