A skilled veterinarian can make an educated guess early in the pregnancy by palpating the abdomen. After that, the only way to know for sure if to take a radiograph late in the pregnancy (cartilage will not show up well, you have to wait for the fetus to have calcified bones to be visible). Weight gain, enlarged nipples and behavior changes can be indicators. Keep in mind, it’s fairly common for bitches to have “false pregnancies” – the weight gain, nipple enlargement and nesting behavior are not sure signs. Gestation is 63–65 days.