Doctors tend to err on the side of being over cautious in relation to bleeding at any stage of pregnancy. Although the amount of blood is small most doctors would regard light bleeding or spotting as a threat of possible miscarriage. Your wife should rest and not engage in physical exertion for the next twenty-four hours. If the bleeding increases she should contact her GP without delay. However, most episodes of spotting subside within a day but can recur again. I have dealt with many women over the years that experienced several episodes of spotting on the same pregnancy and subsequently went on to deliver perfectly healthy normal babies. Best of luck!