Can you get your period while you're pregnant?

I've heard many mothers say, "I didn't know I was pregnant until I was a few months along because I got my period even when I was pregnant." Many women operate under the impression that it is possible, or even common, to menstruate during pregnancy. Although bleeding and spotting can happen during the early stages of pregnancy, it is by-definition biologically impossible to menstruate while pregnant.
If you believe that you may be pregnant and believe you may be menstruating, here are some points to consider.
1. Bleeding in pregnancy looks and feels different from menstruation.
During the early stages of pregnancy, many women do develop some spotting. This is usually caused by implantation, when an embryo embeds itself in the lining of the uterus. It may be a dark brown color or a neutral pink-red. Implantation bleeding is very light. Although it might be necessary to use a panty liner for a day, you are probably not pregnant -- or you are experiencing a miscarriage -- if you bleed enough to soak a tampon or pad.
2. Many women bleed during the first trimester.
Bleeding in early pregnancy isn't always a sign of a serious problem. If you have had a positive pregnancy test, you are almost certainly pregnant, even if you are experiencing some blood loss. Spotting in early pregnancy is not a sign that you should disregard a positive pregnancy result. Nearly one in three women will experience some spotting in early pregnancy, and about half of those women go on to have normal pregnancies.
3. Menstruation-like bleeding is a sign of more serious problems.
If you have had a positive pregnancy test and are bleeding as much as you do during your period, you are likely experiencing severe pregnancy complications and your unborn baby's life is in immediate danger. About half of the pregnant women who experience spotting will go on to have more significant bleeding, which is symptomatic of ectopic pregnancy, molar pregnancy or miscarriage. Call your doctor immediately or go to an emergency room if you are pregnant and experiencing more than a trace amount of bleeding.

4. Cramping occurs in both pregnancy and menstruation.
If you have cramping along with bleeding, this is not an indication that you are or aren't pregnant. Menstrual-like cramps are very common during early pregnancy, although severe pain is not normal. In pregnancy, cramping is the result of normal changes occurring inside the uterus, including the development or rupture of internal cysts. If you are experiencing unusually severe cramping along with bleeding, you may be dealing with a miscarriage.
5. Get expert help if you're concerned.
If you have mild spotting in pregnancy that goes away after a day or two, your baby is probably safe. However, you should tell your physician or midwife so she has a complete picture of the health of your pregnancy. If you have a significant amount of bleeding and do believe you are pregnant, emergency medical care is essential to protect your health and the baby's. Always defer to an expert's judgment if you are concerned about your health.