It's not possible to have three actual menstrual periods in 1 month and still have signs of being pregnant. It's possible, however, to have three bleeding episodes that look like periods in 1 month and still be pregnant. Menstrual bleeding is the sloughing off of the uterine lining when no pregnancy occurs and hormone levels drop. So actual menstrual bleeding and pregnancy can't coexist, but bleeding and the early symptoms of pregnancy can.
The first day of bleeding in a new menstrual cycle is counted as day 1. Day 1 of the menstrual cycle is the start of egg recruitment and development. Normally, once a woman gets pregnant, she doesn't have another period; the hormone changes of pregnancy usually make it impossible for the hormone levels to drop enough for a woman to have another period. But true menstrual bleeding would count as one period in a cycle when you thought you had three periods and were still pregnant.
Implantation bleeding occurs when the embryos begins to burrow into the uterine lining. This type of bleeding usually occurs 6 to 12 days after conception, the American Pregnancy Association states. This means that in a normal 28-day cycle, implantation spotting would occur around day 20 to 26. Since the next menstrual period would be due around the 28th day, implantation bleeding usually occurs before a period is due. Implantation bleeding may be accompanied by light cramping, and usually is light, lasting no more than a few days. If you had implantation bleeding about a week before you expected your next period, you might think you were having a second period within a month.
Bleeding in Early Pregnancy
Bleeding occurs in 20 to 30 percent of early pregnancies, the University of Cincinnati reports. Bleeding can be a sign of impending miscarriage or ectopic pregnancy; ectopic means implanted outside the uterus, usually in the fallopian tube. Bleeding can also indicate a cervical infection. Half of the women with bleeding in early pregnancy go on to have a normal pregnancy, according to the American Pregnancy Association. But if you had bleeding early in the pregnancy, around the time you expected a period, you might think you were having your third period in a month.
Around this time, you might also notice that your breasts were more sore than usual, that you were urinating more frequently and were fatigued. These are all signs of early pregnancy. Signs of pregnancy would be quite normal if you were pregnant, which is possible even if it seemed that you had three periods within a month. If you think you're pregnant even if you've had three bleeding episodes in a month, do a home pregnancy test or a blood test ordered by your doctor. If your test is positive, your doctor will probably want to do an ultrasound to make sure the bleeding doesn't have a serious cause.