37 is equivalent to 98.6
First stage of Labor:
(This stage often goes un-noticed, and takes place in the 24 hours following temperature drop)
Temperature FINALLY drops to 98°F from its normal 99,100,101°F (you should have been taking it regularly for a few days)
If you are really committed, the temperature taking does work. You will find her temperature around 99 to 101, and as soon as it starts to drop, below 99, and continues to drop. (now you take it every hour or two) ;you have about 12-24 hours from the start of the drop. When it bottoms out, to 98 or 97.9, then you have about 2-12 hours.
You may find your dam much more restless, and not able to get comfortable. She will stretch out on her side.
You may find her eyes different, they can dilate, and she can stare at you.
She may not want you out of her site. She may go to her whelp box.
She may vomit. She may try to have a bowel movement from the pressure. She may urinate frequent.
She will refuse to eat, and seek a quite spot, like a closet or under a bed.
She may have some mucus discharge, and her Vulva area will become puffier.
The normal body temperature for animals is generally higher than for humans. The normal rectal temperature of a dog is 99.5° to 102.5°F. The normal temperature of a puppy at birth is 96-97°F. The temperature gradually increases with age until it is 100°F at 4 weeks of age.
EDITED TO ADD:
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Whelping Puppies, Breeding Dogs