What Causes a Threatened Miscarriage?

Bleeding during pregnancy can be extremely unnerving and anxiety-inducing. You might be wondering if you're at risk for losing your baby, or if there's an underlying complication. It's important to know that any signs of bleeding while expecting should be reported to a health care provider right away; however, it doesn't always mean that you're experiencing a miscarriage. Sometimes, bleeding during early pregnancy is what is known as a "threatened miscarriage," in which you're experiencing the signs and symptoms commonly associated with a miscarriage, but your pregnancy has a chance of continuing successfully.

We turned to experts to learn more about the causes of a threatened miscarriage, the signs to watch out for, and when to seek medical care.

What Is a Threatened Miscarriage?

A threatened miscarriage is when a pregnant person is experiencing the common indicators of a miscarriage but the pregnancy is not necessarily at risk. If a person is experiencing symptoms of a miscarriage but the fetus still has a heartbeat, their cervix is closed, and their membranes are intact, those signs might point to a threatened miscarriage rather than a potential pregnancy loss. About half of threatened miscarriages turn out to be viable pregnancies that lead to live birth.

What Are the Symptoms of a Threatened Miscarriage?

Bleeding early in pregnancy is the most common symptom of a threatened miscarriage. You might see a light pink smidge of blood on the toilet paper after you wipe, or you could see a heavier bleeding with clots. Some people experience period-like cramps or lower backache as well, while others might also notice an increase in vaginal discharge.

Causes of a Threatened Miscarriage

The reasons for a threatened miscarriage are not well understood, but there are some general theories. A small amount of bleeding may be caused by an embryo burrowing into the uterine lining (called implantation bleeding), or early stretching of the lining to accommodate a pregnancy.

Damage to the cervix, such as due to a fall or injury, might also be the reason for vaginal bleeding. In some cases, a vaginal infection or a blood clot close to the amniotic sack may be the cause.

About half of the time, an impending, actual miscarriage is the reason for early signs like cramps and bleeding. Miscarriages can occur when an embryo isn’t able to continue developing for reasons that range from genetic or chromosome issues to health conditions of the pregnant person. 

How Is a Threatened Miscarriage Diagnosed?

Threatened miscarriage is diagnosed by ultrasound. A health care provider will check for a fetal heartbeat. “We call it a threatened miscarriage if there is any bleeding in the first trimester and the baby still has a beating heart after the bleeding has occurred,” says Greg Marchand, MD, a board-certified OB-GYN in Arizona.

The presence of a heartbeat tells you that your fetus is still alive, and indicates that this could be a threatened miscarriage. Conversely, a lack of heartbeat indicates a pregnancy loss. 

A provider will also look to see if your cervix has dilated and check if your membranes are still intact. “If we see a closed cervix, we call it a threatened miscarriage because there are signs of possible, but not certain, pregnancy loss,” says Kecia Gaither, MD, MPH, MS, MBA, FACOG, a board-certified OB-GYN, maternal-fetal medicine doctor, and the director of perinatal services and maternal-fetal medicine at NYC Health + Hospitals.

On the other hand, if your body has begun to dilate or your membranes have broken, this is considered an impending or inevitable miscarriage. Even with a heartbeat, these are signs that the pregnancy is ending. “An open cervix tells us that your body is preparing to pass the pregnancy and a miscarriage is inevitable,” says Dr. Gaither. 

How Is a Threatened Miscarriage Treated?

There is no specific treatment for a threatened miscarriage. A health care provider may advise you to rest and be extra cautious not to exert yourself, but this is generally a wait-and-see approach. 

“Some people will feel better after resting...but there is no treatment for a [threatened] miscarriage and no proven therapies to reduce the chance of a miscarriage occurring,” says Dr. Marchand.

If your symptoms subside and your pregnancy continues, a miscarriage is no longer threatened. But, if your symptoms increase and you do miscarry, there isn’t necessarily anything you can do to prevent that from happening.

Can You Prevent Miscarriage?

Most miscarriages cannot be prevented. It is estimated that about a quarter of pregnancies end in miscarriage during the first trimester. These miscarriages may happen because of genetic issues that do not allow the embryo or fetus to continue to develop. 

You might be at a higher risk if miscarriage if you smoke or abuse substances, if you’re over- or underweight, if you have certain health conditions, or if you are of an older age.

If you have a history of repeated miscarriages, a health care provider may advise specific protocols to help increase your chances of a successful pregnancy. You may work with an OB-GYN, or you may be referred to a fertility specialist for this. 

When to See a Health Care Provider

Always reach out to a health care provider any time you notice any amount of bleeding during pregnancy. They will advise you about whether or not you need to be seen, and how soon. “Any bleeding during pregnancy—be it first, second, or third trimester—requires an immediate evaluation by a health provider,” says Dr. Gaither.

If the bleeding is heavy, you are in significant pain, or you have concerns about an impending miscarriage, you should visit the emergency department at your local hospital or dial 911 if you are not able to get there. While pregnancy loss may not be preventable once it starts to occur, it's important to still seek emergency care, because some miscarriages can be life-threatening to the pregnant person.

Lastly, while these signs above don’t always mean that you are experiencing pregnancy loss, it’s always a good idea to get in touch with a health care provider who can help you learn more and do what they can to make sure both you and your baby are safe.