15 Reasons for Passing Blood Clots in Pregnancy

Pregnant woman being checked with an ultrasound

Passing of vaginal blood or blood clots at any time during pregnancy can be a cause of concern and distress for any woman. However, not all instances of blood clots in pregnancy pose a threat to mother or baby. The seriousness depends on the cause and the trimester of pregnancy. They are of greater concern in the second and third trimesters than in the first and are more likely to lead to an emergency situation then. Call 911 or proceed to an emergency room if you are passing large clots or appear to be hemorrhaging and bleeding through a pad or more in an hour or less.

Bleeding and Clotting

It is important to note clotting factors in blood that activate to seal an injured blood vessel will cause blood to clot naturally soon after bleeding starts. The heavier the bleeding, the more blood there is to clot, and the bigger the clots might be by the time they appear out the vagina. In addition, the longer it takes for the blood to appear, the longer time it has to clot before you see it. Learn the causes of passing blood clot during pregnancy.

First Trimester Causes

First trimester vaginal bleeding with or without blood clots might mean a fetus is in jeopardy. However, the bleeding and any clots rarely present a threat to the mother. The following are the most common causes of passing blood clots during pregnancy in the first trimester.

  • Newly pregnant woman having cramps
    Implantation bleeding: Some women may have spotting or bleeding during implantation six to twelve days after the date of conception, but this is usually of no concern. The bleeding is never heavy but rarely may be accompanied by tiny clots.
  • Abnormal pregnancy: An abnormal pregnancy that fails to implant in the uterus or grow normally may cause uterine cramps, bleeding, the passage of small clots, and a subsequent miscarriage or other means of pregnancy loss. Abnormal pregnancies include:
    • Those with abnormal chromosomes and other defects
    • Ectopic pregnancies, which implant outside the uterus
    • Molar pregnancies, which are grape-like clusters of embryonic tissue in the uterus
  • A first trimester miscarriage: Any cause of a first trimester miscarriage can result in vaginal bleeding and clots as the pregnancy separates from the uterine wall. Types of miscarriages include:
    • A threatened miscarriage, where the pregnancy might continue or eventually miscarry
    • A completed miscarriage, where all the pregnancy has passed out of the uterus as blood, clots, and pregnancy tissue
    • An incomplete miscarriage, which means there is still blood, clots, and tissue that needs to come out of the uterus

Second Trimester Causes

During the second trimester, the following causes of vaginal bleeding can also present with passage of blood clots from the vagina. Bleeding can be heavy enough to threaten the life of a mother or her fetus.

  • Upset pregnant woman experiencing abdominal pain
    A second trimester pregnancy loss: A miscarriage after 12 weeks and up to 19 and 6/7 weeks can cause a greater amount of bleeding and passage of larger clots than during the first trimester because the placenta, blood supply, and fetus are larger. At 20 weeks or after, the pregnancy loss is referred to as a stillbirth, and bleeding with clots can occur as part of the process.
  • Preterm labor: After 20 weeks of pregnancy during the second trimester, uterine cramps and bleeding can be signs of preterm labor. Depending on the cause and the amount of bleeding, clots might be seen.
  • Placenta previa: When the placenta implants near the opening of the cervix instead of higher in the uterus, it can partially or completely cover it. This increases the chance of bleeding from the placenta and the passage of blood clots.
  • Vasa previa: Blood vessels from the umbilical cord can insert in the fetal membranes near the cervix instead of the placenta. Such vessels are vulnerable to rupture if undiagnosed and cause bleeding and clots if they do.

  • Placental abruption: If any part of the placenta detaches from the wall of the uterus prematurely, blood and clots can pass through the cervix and into the vagina. A placental abruption is more common after 20 weeks of pregnancy. It can be accompanied by abdominal pain and a hard uterus.
  • Uterine rupture: The most frequent causes of uterine rupture include a previous type of cesarean section, a history of surgery on the uterus, or excessive use of pitocin to induce labor. Most of the bleeding is inside the belly, but vaginal bleeding with clots can occur.

Placenta previa, vasa previa, and placental abruption can be obstetrical emergencies. They can quickly lead to early delivery of a still premature baby or to the death of mother and baby if bleeding is moderate or severe and cannot be controlled.

Third Trimester Causes

Causes for passing blood clots while pregnant in the third trimester include:

  • Pregnant woman in labor at the hospital
    Preterm labor: As in the second trimester, bleeding and passing of blood clots during the third trimester can be caused by preterm labor before 37 weeks. Bleeding might be heavy and the clots large depending on the cause of the preterm labor.
  • Term labor: Passing of a small mucous bloody clot can occur at or close to term. This mucous "bloody show" can mean the passage of the mucous plug from the cervix and usually marks the onset of labor. A blood clot with discharge during pregnancy near the end of term might indicate labor is on the horizon.
  • Abnormal implantation of the placenta, placental abruption, and uterine rupture as noted above for second trimester causes may also occur in the third trimester. Uterine rupture is more common in the third trimester than the second, as well as near or during labor.

Hemorrhaging and passing clots during the third trimester can present a bigger threat to baby and mother if the cause is a placenta previa, vasa previa, or a placental abruption.

Any Trimester Causes

In any trimester of pregnancy the following cervical problems can cause passage of blood and clots from the vagina:

These conditions can be more active in pregnancy and cause the cervix to bleed easily and be a source of passing small vaginal clots throughout pregnancy. The bleeding and clots from these causes may increase after intercourse but will rarely be heavy.

Gauging the Amount of Bleeding and Clots

Passing clots while pregnant can be concerning at any stage. It is useful to keep an eye on how many pads you use during any bleeding in pregnancy. Doctors use this "pad count" to gauge the amount of bleeding as follows:

  • Severe: Passing blood and clots enough to soak through a pad in one hour for two consecutive hours or more
  • Moderate: Bleeding through a pad in three hours
  • Light: Soaking less than a pad in three hours
  • Minimal: Just a few spots of blood on the pad in two to three hours

Do not use tampons at any time during your pregnancy.

When to Seek Help

Bleeding in pregnancy can be accompanied by the passage of clots. Not all bleeding and clots lead to a poor maternal or fetal outcomes, but some can. Follow these guidelines if you have bleeding and/or clots during pregnancy:

  • Consult your doctor or midwife for advice if you notice any vaginal blood or blood clots at any time during your pregnancy.
  • Go in for an evaluation if your bleeding and clots are moderate.
  • Call 911 or proceed to an emergency room if your bleeding is severe, and you are passing big clots, no matter how far pregnant you are. If your bleeding and clots are heavy and large, you may become lightheaded, dizzy, and lose consciousness.

Managing Concerns

Any type of bleeding during pregnancy can be stressful for moms to be. However, following these guidelines will help you manage your concerns or distress and ensure that you and your baby can quickly get the help you need.

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15 Reasons for Passing Blood Clots in Pregnancy