Miscarriage Rates by Week: Statistics and Risk Factors

Miscarriages are more common early in pregnancy. About 80% of pregnancy loss occurs during the first trimester. The risk of miscarrying decreases as the pregnancy progresses. It is important to note that in almost every case, pregnancy loss is not the fault of the birthing person. Miscarriages are typically random events, and the exact cause is usually unknown. 

This article discusses the miscarriage rates by week and the common risk factors. Learn the symptoms of pregnancy loss and when to seek medical care. 

On average, people do not find out they are pregnant until week 5 or 6 of their pregnancy. As a result, as many as half of all pregnancies may end in miscarriage before the pregnancy is known.

A pregnancy that ends during the first five weeks of gestation is called a chemical pregnancy. This is because there may have been a positive pregnancy test due to the initial presence of the pregnancy hormone human chorionic gonadotropin (hCG).

However, the embryo implantation is not complete, and the pregnancy ends.

If someone does not know they are pregnant, they may mistake the bleeding for a delayed period and not realize they experienced pregnancy loss.

The most common cause of miscarriage during these first weeks of development is chromosome problems. These cause genetic abnormalities. The body spontaneously aborts the fetus as it cannot survive.  

Learn more about chemical pregnancy.

The risk of miscarriage is still elevated during the second half of the first trimester. The Office on Women’s Health reports that 10–15% of pregnancies end in pregnancy loss before week 13.

The American College of Obstetricians and Gynecologists reports that around 80% of all pregnancy losses occur during the first trimester.

As in the early weeks of pregnancy, the most common cause of miscarriage is chromosomal abnormalities. As the fetus develops, genetic problems cause the fetus not to develop as expected.

It is also possible for an undiagnosed underlying condition, such as autoimmune conditions or endocrine disorders, to cause pregnancy loss.

An ectopic pregnancy is when the fertilized egg implants somewhere other than in the uterus, most often in the fallopian tube.

The fetus of an ectopic pregnancy is not viable or able to survive. When a medical professional diagnoses an ectopic pregnancy, treatment may include surgery or medication to help stop the growth of the pregnancy. 

Learn more about ectopic pregnancy, including symptoms and treatment.

A 2022 overview reports that the risk of pregnancy loss is relatively low after week 15 of pregnancy.

According to the March of Dimes, a nonprofit organization that advocates for healthy parents and babies, the chance of miscarriage after the first trimester decreases to between 1–5%.

While less common, late pregnancy loss can have a significant physical and emotional impact on the birthing person and their family.

While many times the cause of the miscarriage is unknown, many factors may contribute to late pregnancy loss.

These include anatomical conditions such as:

• Septate uterus: This is when an extra muscle or tissue band separates the uterus into two sections. This is a condition a person is born with and is treatable with surgery before pregnancy.
• Asherman syndrome: This is when scars or scar tissue in the womb damage the lining of the uterus. Asherman syndrome is a common cause of repeat miscarriages.
• Fibroids: Fibroids are growths in the lining of the uterus. They can limit the growing space for the fetus and interfere with the blood supply. 
• Cervical insufficiency: Sometimes called incompetent cervix, this is when the cervix opens too early in the pregnancy.

Other factors that may cause late pregnancy loss include:

• chromosomal abnormalities
• conditions that affect the fetus’ physical development, such as spina bifida
• conditions that increase blood clotting, such as antiphospholipid syndrome (APS)
• autoimmune diseases
• certain infections that may affect the fetus, such as sexually transmitted infections (STIs) or listeriosis, a type of food poisoning

Contact your obstetrician right away if you develop food poisoning or STI symptoms or if you may have been exposed to an STI. Prompt treatment can prevent pregnancy complications for both you and your fetus.

After 20 weeks of gestation, the loss of a pregnancy is considered to be a stillbirth rather than a miscarriage. The medical term for this is intrauterine fetal demise.

Stillbirth is rare, occurring in less than 0.01% of births in the United States each year.

Stillbirths can happen before labor begins. The birthing person may notice their fetus has stopped moving, or the obstetrician may not find the fetus’s heartbeat during a prenatal visit.

A stillbirth may cause you to go into labor and have contractions. On rare occasions, stillbirth can happen during labor.

Many times, the cause of the stillbirth is never known. Some possible causes include:

• genetic disorder or birth irregularity
• placental abruption, which is the early detachment of the placenta from the uterine wall
• placental abnormalities
• blood circulation problems
• infection in the birthing person
• complications during labor and delivery
• problems with the umbilical cord

Stillbirth is a difficult and often traumatic event for parents and families. The National Institute of Child Health and Human Development offers a list of resources for people coping with stillbirth.

While many times the cause of pregnancy loss is unknown, certain risk factors put a person at increased risk of having a miscarriage, including:

• age over 40 years
• history of previous miscarriage
• obesity
• preexisting blood disorders
• high blood pressure
• smoking
• malnourishment
• physical trauma

Talk with an obstetrician if you have miscarriage risk factors and are planning to become pregnant. They can discuss ways to manage the risk factors you can control and provide prenatal care to improve the health of your pregnancy.

Contact your medical professional right away if you believe you are having a miscarriage. Symptoms of an early pregnancy loss include:

• vaginal bleeding or spotting, with or without cramping or pain
• a gush of fluid from the vagina
• passing tissue from the vagina

In early pregnancy, a small amount of bleeding is common and does not necessarily mean you are experiencing a miscarriage. If your bleeding becomes heavy or you develop cramping, or you have any symptoms that cause you concern, contact your OB-GYN immediately. 

These are some questions people often ask about miscarriage rates by week. Tahirah Redhead, MPAS, PA-C, MPH, has reviewed the answers.

Most miscarriages (80%) occur during the first 12 weeks of pregnancy. 

Most miscarriages happen in the first trimester of pregnancy, often before week 6. This may be due to genetic disorders that cause abnormal growth of the fetus. 

Autoimmune diseases or blood clotting disorders can also cause recurrent miscarriage. Talk with your doctor if you experience three or more miscarriages to determine if you have an underlying condition requiring treatment.

After seeing the fetal heartbeat at 6 weeks, the chance of miscarriage is 10–15%. The risk decreases as the pregnancy progresses and is relatively low after 15 weeks.

The risk of miscarriage is highest during the early weeks of pregnancy, affecting 10-15% of confirmed pregnancies. The risk decreases significantly after the first trimester.

After week 20, pregnancy loss is known as stillbirth rather than a miscarriage. The risk of stillbirth is very low, but it can be a traumatic event when it does occur.

Talk with your doctor if you plan to become pregnant about how you can manage risk factors and work together toward a healthy pregnancy.