This link explores possible complications and other details http://www.sniksnak.com/cathealth/howto15.html
Please keep her inside. I own an animal rescue org and one of the most common events we come across are pregnant cats who decide to 'nest' somewhere they feel is safe and where their family can't find them. Months later the female is pregnant again and quite often not at all interested in going back home. As for the kittens, many of them are victims of other predators, parasites and disease. The ones that live will be breeding before they're a year old.
Once she has her babies, you can extend her life by having her spayed. This greatly reduces her chances of breast cancer and an often life threatening disease called pyometra. When the complications of being fully intact happen, and hundreds of dollars are required to correct it (sometimes thousands) the spay surgery sure seems like a pretty good idea.
To better predict her delivery: start taking the temp at the same time, every day and record it. Normal is between 100.5 - 102.5 degrees. When it's about 2-3 days prior to what your calculations indicate is delivery time, take the temp every morning and evening. A drop of approximately 1 degree (or slightly more) will often mean that delivery is impending, usually within 24 hours.
Cats absolutely need privacy, quiet and a sense of safety and security when delivering. An audience, noise or well meaning humans trying to "help" can stress a cat out to the point of their moving the newborn kittens and putting them in danger; becoming aggressive or cannibalistic toward the kittens or abandoning the kittens. Rarely does a cat need ‘help' - especially if a check up is undertaken at the vet before delivery, confirming overall health of mom and babies.
Leaving mom and babies alone for the 24-48 hours after birth is essential. Do not attempt to change the bedding at this time. Do not bring visitors in to see the kittens. No one should handle the little ones until their eyes open, about 7-10 days and even then, limited handling is recommended as they are still very fragile and mom may be uncomfortable with the interference.
DELIVERY COMPLICATIONS
If contractions last an hour without producing a kitten, this is an emergency situation. Quickly and carefully get your cat and any kittens she may have already had, to your vet.
If you're sure there's a placenta being retained after your cat has finished giving birth, she needs to be seen by your vet quickly. Retained placentas cause uterine infections that are often life threatening.
If a kitten does not emerge from the birth canal in 10 minutes, this is an emergency and you need to be prepared to intervene.
Make sure you have your vet's number and directions on hand for the delivery. You'll need to know where to go in the middle of the night on a weekend too - 'just in case'.
Good luck
It sounds like you're being very attentive and that's refreshing.
Heats will vary with environmental conditions, age and even the type of cat it is. They can last a few days, but occur every 3 weeks to a month until she's pregnant (or until the weather changes/daylight shortens).
I've had some queen siamese who seemed to be in nonstop heats until mated (I used to own a cattery).
If you're wondering how long and perhaps how often she mated while in heat, an approximation would be 3 to 5 days and she may have become impregnated by as many males (if she did this on her own).
Please let me know how you make out ok?
You can ask as much as you want - and even after the question is closed, you can re open it any time.
The nipples aren't nearly as good an indicator for delivery as the temp is. What you've noticed though does indicate that she's at the end of her pregnancy and likely due this weekend from what you've explained about her breeding opportunities.
Own Animal Care org.
Animal Rescue&Care Org Owner; Animal Care author; Animal Behavior Consults.;Cert. Avian Specialist;