During a dog's labor, there are several stages the expecting mother will undergo before the pups are born. Just before the labor begins, the dog's temperature will begin to drop from 101 Fahrenheit to under 97 degrees Fahrenheit. After this drop in temperature, your dog will enter stage one of labor in which her cervix begins to dilate in order to allow the puppies to emerge. Although this stage happens internally, there are many signs the dog will exhibit that will help you know the dog has begun to dilate.
Take the dog's temperature every day at noon two weeks before the dog's estimated due date. Keep track of the temperature of the dog --- when the temperature goes below 97 degrees your dog has begun the first stage of labor and is likely slightly dilated. The puppies should be born within a 24 hour period of this temperature drop.
Look for signs that your dog is in discomfort. Contractions that come along with dilation of the cervix are quite painful and your dog will exhibit physical signs that she is in pain. Look to see if she is panting or shaking --- this is a sure sign she has become dilated.
Keep an eye on your dog's eating habits. When it comes time to give birth and the dog is dilated, she will often reject food and may even vomit.
Watch your dog to see if she begins exhibiting any nesting behaviors. One of the key signs that your dog has reached the first stage of labor and is dilated is that she will begin to occupy herself with building a nest for her puppies. She may even retreat to a safe hiding place that she feels comfortable giving birth in.
Listen to any strange noises, whimpering or whining your dog makes. When the dilation occurs it is very painful --- the process lasts almost 16 hours and the dog will be in a lot of pain as it progresses. Your dog will give you verbal cues when she has become dilated.