Each month the uterus builds up a lining to prepare for the implantation of an embryo. If a woman is not pregnant, she sheds the lining in a process commonly referred to as a menstrual period. When a woman is pregnant, she stops having this monthly menstrual period. Although vaginal bleeding is abnormal during pregnancy, up to 10 percent of pregnant women bleed during some portion of the pregnancy and the first trimester is the most common time for the bleeding, according to Medline Plus, a publication of the National Institutes of Health.
A miscarriage is a spontaneous pregnancy loss that occurs during the first half of a pregnancy, and is most common in the first trimester. About 15 to 20 percent of pregnancies end in miscarriage, according to the American Congress of Obstetricians and Gynecologists. The majority of miscarriages occur because the baby is not developing normally. Bleeding is often the first sign of a miscarriage. The bleeding can begin as vaginal spotting and gets heavier as the miscarriage occurs.
The fallopian tubes connect the ovaries to the uterus. After fertilization, the egg continues to travel through the fallopian tube to implant in the wall of the uterus. Sometimes a fertilized egg implants in the fallopian tube or the neck of the uterus. This abnormal implantation, referred to as an ectopic pregnancy, may occur due to scar tissue in the fallopian tube from conditions such as an infection or endometriosis. This condition is less common than miscarriage and affects about one in every 60 pregnancies, according to the American Congress of Obstetricians and Gynecologists. Symptoms associated with an ectopic pregnancy include pelvic and abdominal pain as well as vaginal bleeding. As the pregnancy progresses, the bleeding may get heavier. Treatment for an ectopic pregnancy includes an injection of a medication called methotrexate to dissolve the pregnancy or surgical removal of the embryo. Heavy vaginal bleeding indicates a rupture of the fallopian tube and emergency surgery may become necessary.
The cervix is the opening to the uterus and is located in the upper portion of the vagina. As a pregnancy progresses, the cervix remains tightly closed. The cervix may begin to bleed for several reasons during pregnancy. Increased blood supply to the area makes the cervix bleed easily if bumped or irritated during activities such as sexual intercourse or a pelvic exam. Cervical cancer or an infection involving the cervix may also cause bleeding, according to the Mayo Clinic.