For the first three weeks or so of pregnancy, you may not notice any changes in the bitch. Some females will become more demanding for attention, their nipples may enlarge slightly, and some may become hungrier. These are not a guarantee of a pregnancy, but are good signs. Bitches can show the same signs during 'false pregnancy,' a hormonal abnormality, which may occur after a bitch has been in heat.
Several methods are available to determine pregnancy. A clear mucoid vaginal discharge may be seen. It is a reasonably reliable sign of pregnancy and is noticed about 4-5 weeks into pregnancy and continues until parturition. Ultrasound is able to pick up fetal heartbeats at about 28 days into gestation. This will not be able to determine the number of puppies but can give an estimate and can confirm a pregnancy. At about the same time, a veterinarian may be able to palpate the uterus and feel the fetuses. This may not be possible on a large dog or one that has the puppies under the rib cage. A blood test to check for pregnancy is available. It checks for the hormone, relaxin, which is produced when the fertilized egg implants.
The test can be done about 28-30 days into the pregnancy. Small litter sizes (less than 3 puppies) may result in a false negative result. X-rays can be taken around the 60th day of pregnancy to confirm a pregnancy, count the number of fetuses, and determine size-wise if the puppies will fit through the birth canal.