How is spotting different from bleeding?
Spotting is very light bleeding, similar to what you may have at the very beginning or end of your period. It can vary in color from pink to red to brown (the color of dried blood).

What can cause spotting?
Because of an increase in the blood supply to your cervix and greater blood flow to the area, you might spot after having a Pap smear, an internal exam, or sex. Other causes include:

Implantation bleeding You may have very scant "implantation bleeding," possibly around 11 or 12 days after fertilization (close to the time you might notice a missed period). It may be caused by the fertilized egg burrowing into the wall of your uterus — a process that starts just six days after fertilization — but no one knows for sure. The bleeding is very light, lasting only a day or two, and only a minority of pregnant women have this kind of spotting at all.

Miscarriage Spotting can be an early sign of miscarriage or an ectopic pregnancy, especially if accompanied by abdominal pain or cramping. Ectopic pregnancy occurs when the egg implants itself outside the cavity of the womb, usually in the Fallopian tube. About one quarter of pregnant women have some spotting or bleeding in early pregnancy, and about half of these women miscarry. But if you have an ultrasound that shows a heartbeat between 7 and 11 weeks, your chances of continuing the pregnancy are greater than 90 percent.

Infections Spotting can also be caused by conditions unrelated to pregnancy. A vaginal infection (such as a yeast infection or bacterial vaginosis) or a sexually transmitted infection (such as trichomoniasis, gonorrhea, chlamydia, or herpes) can cause your cervix to become irritated or inflamed. An inflamed cervix is particularly susceptible to spotting after sex or after a Pap smear. You may also spot or bleed after sex or a Pap smear if you have a cervical polyp (a benign growth).

Placental problems or premature labor In the second or third trimester, bleeding or spotting can signal serious conditions such as placenta previa (when the placenta develops low in the uterus, sometimes over the cervix), placental abruption (in which the placenta separates from the uterus), a late miscarriage (between 13 and mid-pregnancy), or premature labor (between 20 and 37 weeks).

Normal labor A mucus discharge that's tinged with blood after 37 weeks is most likely just a sign that the mucus plug has dislodged and the cervix is beginning to soften or dilate in preparation for labor. You should still report any other bleeding or spotting at this point to your practitioner.

Unknown In some cases, the cause of the spotting will remain a mystery. About 20 weeks into her first pregnancy, teacher Laura Graff discovered she was spotting. Her doctor was concerned, so he put Graff on light bedrest, meaning she had to skip exercising, stop having sexual intercourse, and avoid lifting heavy objects for three weeks. After a week, the spotting stopped. Her doctor never figured out why it had happened, and Laura's son, Kevin, was born healthy at full-term.