I keep hearing about women who have babies but didn't know they were pregnant until they went into labor. Does this mean that they were menstruating throughout the pregnancy? Can you be pregnant and still have periods?

H.

Although this a frequent concern that many women ask about, having periods throughout a pregnancy, or not knowing whether you are pregnant until you deliver, is quite rare. Symptoms of pregnancy include absent periods, breast tenderness, fatigue and frequent urination. So, how can pregnancy be missed?

First, conditions that mimic the signs and symptoms of pregnancy may create confusion. One possible scenario might involve a woman with irregular periods due to infrequent ovulation, as might occur with a condition such as polycystic ovary syndrome (PCOS). Even though women with PCOS may have only one or two spontaneous periods each year, these periods may actually follow a rare instance of ovulation. If she has intercourse at the right time, she may get pregnant.

"OK," you say, "I can see how the absence of periods in women who rarely have them anyway would not alert them to the possibility of pregnancy. But don't they notice their enlarging stomachs and feel the baby move?" Maybe not. About half the women with PCOS are overweight. And PCOS can be associated with enlarged, painful ovaries that can cause abdominal discomforts similar to those that may occur with pregnancy. So a woman who is already used to a condition that produces symptoms similar to pregnancy may end up with an unexpected delivery.

In another possible situation, the menstrual cycle apparently continues normally. "Wait," you ask. "You mean I can still have menstrual periods even if I am pregnant?"

No, you don't have "real" periods. That would mean that you are still ovulating monthly, and that just doesn't happen while you are pregnant. Rest assured, once you're pregnant, you can't get pregnant again the next month. But you may have bleeding that is not a period. It may be from the endometrium; hormonal levels fluctuate widely in the first week or two of pregnancy and may result in a "last menstrual cycle" as the pregnancy gets started. Also, implantation bleeding is often experienced as light bleeding a few days prior to the expected menstrual period. Infection, intercourse, uterine polyps, irritation and trauma to the cervix, or threatened miscarriage may also result in bleeding that may be confused with a normal period.

Although home pregnancy tests are becoming more reliable, there can still be errors. Even a physician examination may miss an early pregnancy. Blood testing for hCG or a transvaginal ultrasound are the best tools to make sure a pregnancy is accurately diagnosed.