Why Do Stillbirths Happen?

Causes vary based on gestational age and risk factors, or may be unknown

Giving birth to a stillborn baby is a fear that many people have when they are pregnant. People wonder what causes still birth and what they can do to prevent it from occurring. If it happens to you, it's natural to want to understand why stillbirths happen. Unfortunately, doctors do not always have an answer to this question.

What Is Stillbirth?

A stillbirth is a fetal loss that happens after 20 weeks of pregnancy. A fetal loss before 20 weeks is typically referred to as a miscarriage. Stillbirths can be further categorized as early (20 to 27 completed weeks), late (28 to 36 completed weeks), or term (37 weeks or more).

What Causes Stillbirth?

The cause of stillbirths can vary based on gestational age and underlying risk factors, though in some cases the cause is not known. In fact, a 2011 study found that in approximately one-quarter of stillbirths, there is no known probable or possible cause. Here is an overview of the common causes of pregnancy loss after 20 weeks. 

Chromosomal Abnormalities and Birth Defects

Woman being consoled

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Chromosomal abnormalities are known to cause the majority of miscarriages, but certain chromosomal problems and birth defects can also increase the risk of stillbirth.

Chromosomal abnormalities, especially those associated with anatomic abnormalities or birth defects, account for a high percentage of stillbirths.

According to the National Institutes of Health (NIH), around 14% of stillbirths are caused by birth defects or genetic conditions.

Intrauterine Growth Restriction

Intrauterine growth restriction (IUGR) is a condition where a fetus is significantly smaller than expected for the number of weeks of pregnancy. In severe cases, the condition can cause stillbirth or increased risk of newborn loss (perhaps because the baby is not getting adequate oxygen or nutrition).

A pregnant person's health conditions and lifestyle can also increase the risk of intrauterine growth restriction. Healthcare providers screen for these problems during prenatal care. Some specific risk factors are preeclampsia, pregnancy-induced high blood pressure, and smoking in pregnancy.

As part of standard prenatal care, healthcare providers closely monitor fetal growth, which gives them the chance to intervene if a fetus appears at risk.

Placental Abruption and Other Obstetric Complications

Placental abruption is a condition in which the placenta suddenly separates from the wall of the uterus during pregnancy while the fetus is still in the womb.

This can happen because of a pregnant person's health conditions, trauma to the abdomen in later pregnancy, or structural abnormalities in the uterus. Lifestyle factors, such as smoking or substance use, can also increase the risk.

Placental abruption can cause abdominal pain, contractions, and vaginal bleeding. If you experience any of these symptoms while you are pregnant, contact your healthcare provider immediately.

Other obstetric complications, such as multiple gestations and low amniotic fluid, are also believed to be contributing factors in some stillbirths. 


Certain bacterial and viral infections, including sexually transmitted infections (STIs), can increase the risk of stillbirth. Infections are a factor in about 13% of stillbirths.

Umbilical Cord Accidents

Cord accidents during pregnancy, such as a tight knot in the cord or the cord becoming too tightly wrapped around the baby's neck, are rare. About 10% of stillbirths are related to cord abnormalities.

Pregnancies Far Past Due Date

Studies show that pregnancies past 42 weeks gestation are at increased risk for stillbirth—perhaps because the placenta beings losing its ability to support the fetus.

To avoid complications, healthcare providers usually recommend inducing labor at or before 42 weeks gestation.

Medical Conditions

Several medical conditions a pregnant person might have are also associated with an increased risk of stillbirth. This could be a condition that a person had before becoming pregnant or one that developed during pregnancy.

Health conditions that might contribute to stillbirth include:

If your pregnancy is complicated by any of these conditions, your healthcare provider might recommend additional testing and/or delivery before your due date.

2 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Stillbirth Collaborative Research Network Writing Group. Causes of death among stillbirthsJAMA. 2011;306(22):2459-2468. doi:10.1001/jama.2011.1823

  2. National Institutes of Health (NIH), Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). Placental, pregnancy conditions account for most stillbirths.

Additional Reading

By Krissi Danielsson
Krissi Danielsson, MD is a doctor of family medicine and an advocate for those who have experienced miscarriage.