Your body goes through so many changes during pregnancy. While many of the adjustments are expected (and even fun!), others can be concerning. For example, any sign of blood, or a blood clot, can be distressing. But passing blood clots during early pregnancy doesn't always mean that something is wrong with you or your baby.
Vaginal bleeding during pregnancy has many causes. Up to 25% of pregnant people experience bleeding in the first trimester, and 3% - 4% experience bleeding in the second and third trimesters. Heavy bleeding, however, can sometimes be a sign of something more serious, so it's important to get checked by your healthcare provider to determine the cause.
Possible Causes of Blood Clots in Early Pregnancy
Vaginal bleeding in the first trimester of pregnancy is common. Possible causes of first-trimester bleeding include:
- Chemical pregnancy.When an embryo implants into the uterine lining but does not develop any further (beyond 5 weeks gestation). A chemical pregnancy may cause light spotting that progresses to heavy bleeding, including clots.
- Ectopic pregnancy. Occurs when a fertilized egg implants outside of the uterus, such as in the fallopian tube.
- Implantation bleeding. Implantation occurs when a fertilized egg (embryo) burrows into the uterine lining to continue development in the uterus. Implantation bleeding is typically light and is not a cause for concern.
- Subchorionic hematoma. A blood clot between the amniotic membrane and uterine wall. Occurs most often between 10 to 20 weeks of pregnancy and accounts for 11% of all vaginal bleeding during pregnancy.
Sometimes, bleeding and passing blood clots in the first trimester can be a sign of miscarriage. Other signs of miscarriage include cramping and back pain. If you experience bleeding of any kind, especially blood clots, talk to your healthcare provider.
Potential Causes of Blood Clots in the Second and Third Trimesters
During the second and third trimesters, vaginal bleeding and passing blood clots can be a sign of something more concerning. But many of the conditions that cause bleeding are quite rare. Possible causes of bleeding in the second trimester and third trimesters include:
- Placenta previa. This condition occurs when the placenta covers the opening of the birth canal (cervix). Placenta previa can cause bright red vaginal bleeding that is usually painless. Certain events can trigger the bleeding, such as intercourse or a medical exam.
- Placental abruption. Occurs when the placenta partially or completely detaches from the wall of the uterus. This can decrease the amount of nutrients and oxygen the baby receives and cause heavy bleeding. Other placental abruption symptoms include abdominal pain, blood clots, and back pain.
- Vasa previa. Occurs when fetal blood vessels run through the amniotic membranes and cross over the cervix. Vasa previa is very rare, occurring in 0.46 out of every 1,000 pregnancies. Symptoms include painless and excessive vaginal bleeding, membrane rupture (water breaking), and abnormal fetal heart rate.
- Uterine rupture. Occurs when a uterine scar from a previous c-section rips open during pregnancy or labor. Uterine rupture is rare, occurring in only 0.5% of pregnancies. Excessive bleeding and abdominal pain and tenderness are common symptoms of uterine rupture.
- Preterm labor. In some cases, vaginal bleeding and blood clots may be a sign that your body is preparing to give birth. If bleeding occurs before you are full-term (37 weeks), your healthcare provider may try to stop labor to give your baby more time to develop in utero. Symptoms of preterm labor include contractions, lower back pain, and membrane rupture.
- Term labor. After 37 weeks, you are considered "full term" and can give birth at any time. As your body prepares for labor and delivery, you may pass your mucus plug - a thick piece of mucus that covers your cervix. Your mucus plug may be tinged with pink or red blood. Passing your mucus plug along with blood or a blood clot may be a sign that you will soon be giving birth.
Bleeding heavily and passing blood clots in the second and third trimesters may be a sign of an emergency. Contact your healthcare provider immediately so they can check on the health of you and your baby.
Possible Causes of Blood Clots During Any Trimester
At any point in pregnancy, the following may cause vaginal bleeding and blood clots:
- Cervical polyps. Finger-like growths that connect the uterus to the cervix.
- Cervicitis. Inflammation of the cervix that may occur due to an infection of the cervix
- Cervical ectropion. When cells on the inner portion of the cervix become exposed and visible near the vagina.
- Uterine fibroids. Noncancerous uterine growths that may cause bleeding. Up to 30% of people with uterine fibroids experience bleeding during pregnancy.
Pregnancy may exacerbate some of these conditions, leading to the passing of small blood clots and bleeding.
Remember that although bleeding in pregnancy is usually unexpected, it is not uncommon, especially in the first trimester. But bleeding of any kind during pregnancy can be stressful and worrisome for expectant parents, so it's always best to err on the side of caution and get checked by your healthcare provider for peace of mind.