Many women equate bleeding during pregnancy with miscarriage, for good reason. Miscarriages do, in fact, involve bleeding, but while bleeding may herald miscarriage, it doesn't necessarily have to. In fact, with all the changes a woman's body goes through early in pregnancy, there are many good reasons for light bleeding. Pink bleeding, in particular, is likely quite light, since blood has mixed with other vaginal fluids to yield a less concentrated, lighter flow.
The early weeks of pregnancy can be confusing for women, especially because it is very hard to tell exactly how far along a pregnancy is early on. Technically, pregnancies begin with the start of a woman's last menstrual period, meaning a woman is at least two weeks pregnant before she even conceives, explain Heidi Murkoff and Sharon Mazel, in their book "What To Expect When You're Expecting." Since it's not uncommon for ovulation to occur slightly early or late relative to the last menstrual period, a woman who thinks she's five weeks pregnant is likely somewhere between four and six weeks, though more precise pinpointing is difficult without ultrasound. Bleeding around five weeks, therefore, is actually taking place anywhere from two to four weeks after conception.
Bleeding very early in pregnancy, particularly if the bleeding is light, generally doesn't signify anything of great concern. For instance, a very common cause of light bleeding is implantation of the embryo, which occurs around the time of a woman's missed period. If a woman ovulates a bit late relative to her last menstrual period, implantation bleeding can occur around five weeks of pregnancy. The bleeding is typically light, pinkish or brownish, and more like spotting than an actual period, explains Dr. Raymond Poliakin in his book "What You Didn't Think To Ask Your Obstetrician."
There are a few reasons for non-implantation related bleeding, which can also arise around five weeks gestation. One of these is that the cervix becomes very vascular early in pregnancy, and the blood vessels of the outer cervix are quite delicate. Women often bleed a bit after sexual intercourse due to the penis hitting these vessels, notes Dr. Poliakin. Post-intercourse light bleeding, such as pink spotting, generally isn't an indication that anything is wrong. Light bleeding that becomes heavier with time, however, may be a sign of impending miscarriage, warns Dr. Poliakin. Heavy, red bleeding, particularly if it contains clots, warrants communication with a doctor.
Very rarely, women may bleed periodically throughout pregnancy. Reasons for this vary, but some women actually continue to have light menstrual periods despite their pregnancy. As such, it's theoretically possible that a woman would have her normal menstrual period around five weeks of pregnancy if her cycles tend to run a bit longer than 28 days, or if she's a bit off in her dating of the start of the pregnancy. Other common causes of bleeding, such as placenta previa, in which the placenta covers the cervix and leads to vaginal bleeding, don't occur very early in pregnancy, notes Dr. Poliakin.
As a set of general guidelines, Dr. Miriam Stoppard, author of "Conception, Pregnancy and Birth," recommends discussing any early pregnancy bleeding with a physician. At five weeks, many women don't yet know they're pregnant, but for a woman who has had a positive pregnancy test, early bleeding is a good reason to make an appointment with an obstetrician to check the viability of the pregnancy and make sure everything in progressing normally.