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Third Trimester Bleeding: What Are the Possible Causes?

Third Trimester Bleeding: What Are the Possible Causes?

Third trimester bleeding can feel worrisome for any mother, especially those who are pregnant for the first time. But what exactly are the reasons why this happens, and should you be concerned if you experience it? Read on to learn more.

What is third trimester bleeding?

As the name suggests, third trimester bleeding is bleeding that happens late into pregnancy. About 1 out of 10 women can experience this type of bleeding, and it can be due to a number of reasons which range from mild to serious1.

Should you be worried?

If you do experience third trimester bleeding, you shouldn’t immediately panic. The best thing to do would be to report it to your doctor as soon as you can and inform them of any other symptoms you might have experienced.

This can help them figure out what course of action would be best to address your concerns, and to find out what might have caused the bleeding.

It’s also important to know the difference between bleeding and spotting. Bleeding is when there is a heavy flow of blood coming from the vagina, while spotting is usually just a few drops of blood2.

In most cases, spotting shouldn’t be a cause for concern, but it’s still a good idea to talk to your doctor about it.

What are the possible reasons for third trimester bleeding?

Here are some of the things that can cause third trimester bleeding:

Placenta previa

This is a condition wherein the placenta partially or completely covers the cervix. The exact cause of this condition is still unknown, but there are some risk factors that can increase the chances of it happening, such as the following:

  • Uterine fibroids
  • Scarring because of previous pregnancies
  • Being aged 35 and older
  • Smoking
  • A history of placenta previa
  • Previous surgeries on the uterus, or cesarean section

The biggest risk with placenta previa is a hemorrhage. The reason is that during the third trimester, part of the uterus starts to thin down as it is getting ready for labor.

When this happens, the part of the placenta that’s covering the cervix starts to bleed. In patients with placenta previa, the more their placenta covers the cervix, the more prone they are to having a hemorrhage3.

Placenta abruptio

Placenta abruptio is a condition that can cause third trimester bleeding. This is a condition wherein the placenta gets detached from where it was implanted in the uterus.

When this happens, a number of blood vessels that used to be connected between the placenta and uterus starts to bleed. The more of the placenta is detached, the worse the bleeding can be.

Complications of placenta abruptio can also include stillbirth, hemorrhage during labor, as well as poor blood flow to the kidneys or brain4.

Uterine fibroids

Uterine fibroids are non-cancerous growths that can be found in the uterus. During pregnancy, hormonal changes can cause these fibroids to change in size, and can cause pain as well as vaginal bleeding.

For the most part, uterine fibroids don’t pose a risk to pregnancy. But there are very rare cases where fibroids have increased the risk of preterm birth and miscarriage.


Another possible reason for third trimester bleeding is if it is caused by an infection. What happens is that a bacterial or viral infection has spread through the cervix, and causes inflammation which can lead to bleeding.

Depending on the type of infection, it can potentially cause harm to the baby. So it is important to get it checked as soon as possible.


Lastly, sex can also be a reason for third trimester bleeding. There are some cases wherein women can experience very light bleeding or spotting after having sexual intercourse.

This isn’t usually a cause for concern, but it’s still a good idea to visit your doctor if this happens. It’s always best to err on the side of caution when it comes to you and your baby’s health and safety.

Learn more about the third trimester of pregnancy here.


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Hello Health Group does not provide medical advice, diagnosis or treatment.

  1. Vaginal bleeding in late pregnancy: MedlinePlus Medical Encyclopedia, https://medlineplus.gov/ency/patientinstructions/000627.htm, Accessed July 15, 2021
  2. Vaginal bleeding in late pregnancy | UF Health, University of Florida Health, https://ufhealth.org/vaginal-bleeding-late-pregnancy, Accessed July 15, 2021
  3. Placenta Previa, https://www.stanfordchildrens.org/en/topic/default?id=bleeding-in-pregnancyplacenta-previaplacental-abruption-90-P02437, Accessed July 15, 2021
  4. Bleeding in Pregnancy/Placenta Previa/Placental Abruption | Children’s Hospital of Philadelphia, https://www.chop.edu/conditions-diseases/bleeding-pregnancyplacenta-previaplacental-abruption, Accessed July 15, 2021
  5. Third Trimester Bleeding, https://www.stritch.luc.edu/lumen/MedEd/obgyne/lectures/Third_Trimester_Bleeding.pdf, Accessed July 15, 2021
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Written by Jan Alwyn Batara Updated Jun 15, 2021
Fact Checked by Hello Doctor Medical Panel