Bleeding during pregnancy is common, especially during the first trimester, and usually it's no cause for alarm. But because bleeding can sometimes be a sign of something serious, it's important to know the possible causes, and get checked out by your doctor to make sure you and your baby are healthy.
Bleeding in the First Trimester
About 20% of women have some bleeding during the first 12 weeks of pregnancy. Possible causes of first trimester bleeding include:
Implantation bleeding. You may experience some normal spotting within the first six to 12 days after you conceive as the fertilized egg implants itself in the lining of the uterus. Some women don't realize they are pregnant because they mistake this bleeding for a light period. Usually the bleeding is very light and lasts from a few hours to a few days.
Miscarriage. Because miscarriage is most common during the first 12 weeks of pregnancy, it tends to be one of the biggest concerns with first trimester bleeding. However, first trimester bleeding does not necessarily mean that you’ve miscarried or will miscarry. In fact, if a heartbeat is seen on ultrasound, over 90% of women who experience first trimester vaginal bleeding will not miscarry.
Ectopic pregnancy. In an ectopic pregnancy, the fertilized embryo implants outside of the uterus, usually in the fallopian tube. If the embryo keeps growing, it can cause the fallopian tube to burst, which can be life-threatening to the mother. Although ectopic pregnancy is potentially dangerous, it only occurs in about 2% of pregnancies.
Other symptoms of ectopic pregnancy are strong cramps or pain in the lower abdomen, and lightheadedness.
Molar pregnancy (also called gestational trophoblastic disease). This is a very rare condition in which abnormal tissue grows inside the uterus instead of a baby. In rare cases, the tissue is cancerous and can spread to other parts of the body.
Other symptoms of molar pregnancy are severe nausea and vomiting, and rapid enlargement of the uterus.
Additional causes of bleeding in early pregnancy include:
- Cervical changes. During pregnancy, extra blood flows to the cervix. Intercourse or a Pap test, which cause contact with the cervix, can trigger bleeding. This type of bleeding isn't cause for concern.
- Infection. Any infection of the cervix, vagina, or a sexually transmitted infection (such as chlamydia, gonorrhea, or herpes) can cause bleeding in the first trimester.
Bleeding in the Second and Third Trimesters
Abnormal bleeding in late pregnancy may be more serious because it can signal a problem with the mother or baby. Call your doctor as soon as possible if you experience any bleeding in your second or third trimester.
Possible causes of bleeding in late pregnancy include:
Placenta previa. This condition occurs when the placenta sits low in the uterus and partially or completely covers the opening of the birth canal. Placenta previa is very rare in the late third trimester, occurring in only one in 200 pregnancies. A bleeding placenta previa, which can be painless, is an emergency requiring immediate medical attention.
Placental abruption. In about 1% of pregnancies, the placenta detaches from the wall of the uterus before or during labor and blood pools between the placenta and uterus. Placental abruption can be very dangerous to both the mother and baby.
Uterine rupture. In rare cases, a scar from a previous C-section can tear open during pregnancy. Uterine rupture can be life-threatening, and requires an emergency C-section.
Other symptoms of uterine rupture are pain and tenderness in the abdomen.
Vasa previa. In this very rare condition, the developing baby's blood vessels in the umbilical cord or placenta cross the opening to the birth canal. Vasa previa can be very dangerous to the baby because the blood vessels can tear open, causing the baby to bleed severely and lose oxygen.
Other signs of vasa previa include abnormal fetal heart rate and excessive bleeding.
Premature labor. Vaginal bleeding late in pregnancy may just be a sign that your body is getting ready to deliver. A few days or weeks before labor begins, the mucus plug that covers the opening of the uterus will pass out of the vagina, and it will usually have small amounts of blood in it (this is known as "bloody show"). If bleeding and symptoms of labor begin before the 37th week of pregnancy, contact your doctor right away because you might be in preterm labor.
Additional causes of bleeding in late pregnancy are:
- Injury to the cervix or vagina
What to Do If You Have Abnormal Bleeding During Pregnancy
Because vaginal bleeding in any trimester can be a sign of a problem, call your doctor. Wear a pad so that you can keep track of how much you're bleeding, and record the type of blood (for example, pink, brown, or red; smooth or full of clots). Bring any tissue that passes through the vagina to your doctor for testing. Don't use a tampon or have sex while you are still bleeding.
Your doctor might recommend that you rest as much as you can and avoid exercise and travel.
You should expect to receive an ultrasound to identify what the underlying cause of your bleeding may be. Vaginal and abdominal ultrasounds are often performed together as part of a full evaluation.
Go to the emergency room or call 911 right away if you have any of the following symptoms, which could be signs of a miscarriage or other serious problem: