Vaginal bleeding during pregnancy can occur during any trimester and does not always indicate the pregnancy is in danger (but can). The cause, seriousness, and prognosis is entirely dependent on when the bleeding occurs and if other symptoms are present.
Bleeding early in pregnancy does not always result in miscarriage and can resolve on its own. However, bleeding in the first trimester could also indicate ectopic pregnancy, infection, or other concerns. Bleeding mid-to-late pregnancy could indicate potential problems with the placenta or preterm labor, which can be very serious.
For these reasons, pregnant women should always call their HCP for bleeding at any time during pregnancy, especially if accompanied by abdominal pain, cramping, fever, and/or chills. Further, bleeding late in pregnancy may require a visit to the hospital/emergency department.
Overall, first trimester bleeding is not investigated very often in the research community. It is also very difficult, in most cases, to determine why bleeding is present, especially if the bleeding eventually resolves. Additionally, if a miscarriage does occur, the bleeding is most often attributed to the miscarriage itself.
What is known is that even though miscarriages are almost always preceded by bleeding, bleeding does not necessarily mean a miscarriage will occur.
Bleeding may be a cause of pregnancy loss, the result of a miscarriage, or may occur due to an unrelated reason that does not result in miscarriage.
Bleeding in the first trimester happens to about 15% to 25% of women, and more than 50% to 75% of those women go on to have normal pregnancies. Cramps, pelvic pressure, and low backache can accompany bleeding.
In one study, approximately 1,207 pregnant women reported vaginal bleeding. Most episodes lasted less than three days, and most occurred between 5 and 8 weeks of pregnancy. Of note, only 12% of women with bleeding and 13% of those without bleeding experienced pregnancy loss.
Overall, it appears that:
Spotting and light episodes of bleeding that eventually stop are generally not associated with miscarriage.
In most cases, bleeding during the first 8 weeks of naturally conceived pregnancies seems to occur without a clear cause, and symptoms may resolve as the pregnancy progresses.
Heavy bleeding in the first trimester, when accompanied by pain, is associated with a higher risk of miscarriage. Changing a pad soaked with blood and/or clots more than once an hour is an indication of heavy bleeding and calling an HCP is recommended.
Bleeding may occur from the following scenarios:
Subchorionic hemorrhage: First described in 1981, subchorionic bleeding is the most common cause of vaginal bleeding in women who are 10 to 20 weeks pregnant. Subchorionic hemorrhage is bleeding between the uterine wall and the chorion due to partial separation. The chorion is the outermost membrane of the embryo (diagnosed via ultrasound). Not all subchorionic hemorrhages lead to pregnancy loss, and most tend to clear up on their own.
However, some studies indicate this type of bleeding can lead to pregnancy loss due to increased oxygenation which may interfere with early growth of the embryo and placenta. Subchorionic hemorrhage may also lead to inflammation which could cause contractions and loss of the gestational sac, even prior to the development of the embryo.
Prognosis depends on when the hemorrhage was identified and the size of the bleed (however, some studies have not found an association between size and miscarriage risk). Studies have indicated the earlier in the pregnancy the bleed is identified, the higher the miscarriage risk.
Since subchorionic bleeding does not always leads to loss, there is no specific management. Women are usually monitored with one or two follow up ultrasounds to determine if the bleed has resolved.
Ultrasound images of a subchorionic bleed from a 10-week pregnancy can be viewed here (Critical Care Sonography).
Sex: Bleeding or spotting may occur after sex; the cervix can bleed more easily from any type of contact because more blood vessels are developing in this area (cervical ectropion). Bleeding is usually very light and resolves quickly.
However, it is important for women to tell their HCP anytime this occurs, especially if bleeding is heavier. Although it could be the result of sex, this type of bleeding can also be due to problems with the cervix that could present coincidentally during pregnancy (i.e. polyps). Therefore, it is good practice to rule out other possible conditions.
Physical Exam: For the same reason bleeding occurs after sex, spotting may occur after a pelvic exam by an HCP if contact is made with the cervix (gloved finger, pap smear). Read more about pelvic exams/pap smears during pregnancy here.
Fibroids: Fibroids (leiomyomas) are the most common solid benign masses found in reproductive structures during pregnancy. Approximately 33% to 50% of fibroids grow in the first trimester due to rising estrogen levels; fibroids can cause bleeding in early pregnancy as well as later in pregnancy.
The location of the fibroid appears to determine the risk for bleeding. Bleeding in early pregnancy may be more common if the placenta implants close to the fibroid compared with pregnancies in which the placenta is not in contact with the fibroid.
Although fibroids can cause complications during pregnancy (possible miscarriage, pain, cesarean delivery, preterm labor), they may also have no impact; this depends on size, location of the fibroid, number of fibroids, and type of fibroid.
Threatened miscarriage: With a "threatened miscarriage", bleeding is present, but the cervix is closed; it is possible the pregnancy continues normally.
Inevitable miscarriage: Bleeding, particularly heavy, is present, and the cervix is open; an open cervix is a more ominous sign a miscarriage may occur.
An HCP will likely perform an ultrasound exam in any case of vaginal bleeding during early pregnancy (read First Trimester Viability). The HCP will want to rule out:
Corpus Luteum Cyst Rupture: The corpus luteum (CL) usually breaks down and disappears after 10 weeks of pregnancy, but in rare cases, it can fill with fluid or blood and rupture. Bleeding may be severe, leading to shock. Rupture of a CL cyst is as dangerous as ectopic pregnancy, but occurs less frequently.
Molar Pregnancy: A pregnancy in which abnormal trophoblastic tissue grows into the uterus; categorized as complete or partial molar pregnancy, and severity depends on the level of uterine invasion. Bleeding, pain, and severe vomiting are early signs of this condition.
Bleeding that occurs in the second or third trimesters of pregnancy is often a sign of a potential complication, especially if the bleeding is heavy and/or accompanied by pain. These symptoms usually indicate a problem with the placenta or the start of preterm labor. If a pregnant woman has any bleeding during the second or third trimesters, she should call her HCP immediately or seek emergency care at a hospital.
Placenta Abruption occurs when the placenta detaches from the wall of the uterus before or during birth. The most common signs and symptoms are vaginal bleeding and abdominal or back pain.
Placenta Previa occurs when the placenta lies low in the uterus and partly or completely covers the cervix; painless bleeding is the most sign/symptom of placenta previa. Bleeding may begin without warning and in otherwise completely uncomplicated pregnancies.
Placenta Acreta occurs when the placenta (or part of the placenta) invades and is inseparable from the uterine wall which could cause life threatening hemorrhaging.
Preterm Labor: Vaginal bleeding in the first and second trimester is associated with an increased risk of preterm delivery, as well as preterm delivery itself.
Mucus Plug: The cervical mucus plug falls out in some women sometime between 37 and 42 weeks of pregnancy, while others lose their plug after labor has already begun. The plug can be lost gradually or all at once, and some women will notice streaks of blood within vaginal discharge.
If a woman recognizes more blood than streaks or slight spotting, this is more likely associated with possible placental concerns and she needs to contact her HCP.
Pregnant women should always call their HCP for bleeding at any time during pregnancy, especially if accompanied by abdominal pain, cramping, fever, and/or chills; bleeding late in pregnancy may require a visit to the hospital.
Women experiencing severe pain and bleeding in the first trimester should also seek emergency care.
An HCP will likely ask (to include nursing staff, over the phone):
Date of last menstrual period
Amount of blood
Color/consistency of blood (brown, bright red, or dark red; clots, etc.)
Any accompanying additional symptoms
An HCP will likely also conduct a vaginal or pelvic examination and an ultrasound scan or blood tests to check hormone levels and for signs of infection. However, if a woman is experiencing heavy bleeding in the second or third trimester, a pelvic exam is not recommended due to the possibility of additional – and possibly catastrophic – bleeding from the placenta.
Only an HCP can assess whether or not the cervix is open or closed, and women should not attempt to identify this themselves.
Women should also consider sharing and submitting their experience below regarding vaginal bleeding during pregnancy. This can help other women recognize they are not alone with this concern. It is also important that women who did not experience a miscarriage after bleeding also consider sharing so women understand bleeding does not always end in pregnancy loss.
Bleeding During Pregnancy (American College of Obstetricians and Gynecologists)
Bleeding and/or pain in early pregnancy (U.K Royal College of Obstetricians and Gynaecologists)
Bleeding and/or pain in early pregnancy: Patient Leaflet (U.K Royal College of Obstetricians and Gynaecologists)