The blood that applies in the case mentioned in the question is irregular vaginal bleeding. These drops of blood are not menstruation and do not mean that a pregnant woman should stop praying and fasting.

In Islam, there is no fixed minimum gap between two menstrual periods. A woman should stop fasting and praying when she sees menstrual blood, provided the total bleeding duration does not exceed 15 days per month. Yellowish or brownish discharge after the period ends is not considered menstruation.