Chihuahuas go through three stages to labor.
During the first stage the cervix dilates and contractions begin. Your female will be uncomfortable, restless, pace and pant. This lasts 6-18 hours.
During the second part of labor, your female's contractions begin in ernest. Her water breaks and puppies are delivered usually after 10-30 minutes of pushing. All puppies are born during this stage.
The third stage of labor is after all pups have been delivered and is when a dog still has small contractions to expell fluids and/or placentas from the uterus.You can read more about this here: http://www.2ndchance.info/caninelaborstages.htmIf your dog's water broke or there is a bloody show, then a puppy should be born shortly after that. If your dog is actively straining to deliver a puppy for more than 20-25 minutes, or there is longer than an hour or so between puppies being born and you feel there are more puppies, she needs to be seen by a vet.Sometimes puppies are too large to be born and get stuck. They can also experience uterine intertia and you need a visit to determine if a shot to restart labor is needed.It isn't unusual for there to be from 10 minutes to an hour between puppies being born. So keep an eye on the clock and record the time each puppy is born so you can accurately judge when a vet visit may be needed.Sometimes a female will not push in the house due to house training. Taking her outside with a towel to wrap the puppy in if it should be born can be attempted if you feel this is the case.It is possible for a mother to not deliver all her pups. Usually when a pup is retained, a dog does not act normal. They may appear restless, distressed, actively straining, lethargic, non-interested in their pups.However, if your dog is eating, drinking, urinating, nursing her puppies, cleaning them and basically acting normal, she has most likely delivered all her puppies.If you feel there is a puppy still inside your female, then you should take her to the Vet to be sure. It's a good idea to take her and the pups in anyway for a post whelping checkup to ensure all placentas were delivered as wellHere is a site on this information. http://www.petplace.com/dogs/dystocia-difficult-birth-in-dogs/page1.aspx http://www.peteducation.com/article.cfm?cls=2&cat=1628&articleid=899Chihuahuas frequently need c-sections so at the first sign of problems, I would have her seen.I hope you find this information helpful.