Premature birth occurs before 37 weeks of pregnancy. Some potential causes of premature birth include infections, chronic medical conditions, and multiple pregnancies. Socioeconomic factors can also contribute.

According to the World Health Organization (WHO), birth may be moderately premature at 32–37 weeks, very premature at 28–31 weeks, and extremely premature at under 28 weeks.

Premature birth affects more than 1 in 10 infants born in the United States annually. Premature birth complications are a leading cause of death in children ages 5 and under.

This article examines the causes, risk factors, and possible complications of premature birth. It also looks at relevant statistics and potential prevention methods for premature birth.

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This feature mentions pregnancy loss, stillbirth, or both. Please read at your own discretion.

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Doctors and scientists do not always understand the causes of premature birth, which can be numerous and complex.

However, certain chronic medical conditions may increase the risk of premature birth. These include:

  • Diabetes: Diabetes can contribute to premature birth. This may be because diabetes can alter how some molecules in the body function. A person with diabetes will need to work closely with a doctor to avoid pregnancy complications.
  • High blood pressure: Maternal high blood pressure can prevent enough nutrients and oxygen from reaching the fetus, which may necessitate early delivery.
  • Heart disease: Pregnancy causes changes to the body that may increase stress on the heart. In someone with heart disease, these changes can increase the risk of complications for themselves and the fetus.
  • Antiphospholipid syndrome (APS): People with APS have a higher risk of developing blood clots. Doctors do not know the precise ways in which APS can cause premature birth. Normal changes in the body during pregnancy may increase the risk of blood clot blockages in people with APS, which may lead to premature birth.
  • Obesity: Obesity occurs when a person has excess body fat or weight that can affect their health. Maternal obesity can lead to chronic inflammation, which can affect placental health and the growth of the fetus, and may trigger contractions and early labor.

Learn more about the links between poverty, obesity, and chronic health conditions.

A pregnant person carrying more than one fetus at a time has a higher risk of premature birth.

According to a 2018 article, half of all twin pregnancies result in premature birth before 37 weeks, and 10% of people pregnant with twins give birth before 32 weeks of pregnancy.

The article states that researchers have proposed various potential causes for premature twin birth, which include:

  • increased release of corticotrophin‐releasing hormone, which may trigger premature birth
  • increased levels of a protein called surfactant protein‐A, which can stimulate an inflammatory response in the uterus that may begin labor
  • stretching of the uterus, which can lead to premature birth
  • a higher risk of complications, which may prompt a doctor to induce premature birth medically

Giving birth soon after a previous pregnancy or birth may also increase the risk of premature birth. Doctors do not know precisely why this is but advise waiting at least 18 months between giving birth and becoming pregnant.

Several pregnancy complications may lead to premature birth. With certain complications, doctors often induce labor to cause premature birth and minimize risk to the parent and fetus.

Examples of complications include:

  • Preeclampsia and eclampsia: High blood pressure in pregnancy can be life threatening. Severe cases may necessitate the induction of premature birth.
  • Infections during pregnancy: Infections may affect the health of the parent and the fetus and can weaken the lining of the amniotic sac. Infections that may cause premature birth include:
  • Fetal growth restriction (FGR): In FGR, a fetus is smaller than average and can develop various health complications. Fetuses with FGR are at higher risk of premature birth.
  • Gestational diabetes: Gestational diabetes is a type of diabetes that may occur during pregnancy. It can cause various health complications in the parent and fetus.
  • Placental abruption: In placental abruption, the placenta separates from the uterus lining too soon. This can cause premature birth and various health complications for the fetus and parent.
  • Polyhydramnios: Polyhydramnios occurs when too much amniotic fluid surrounds the fetus, possibly causing early labor.
  • Preterm prelabour rupture of membranes (PPROM): PPROM is when a person’s water breaks too soon before labor. If this happens, a doctor may need to induce early labor.
  • Twin-to-twin transfusion syndrome: In pregnancies where twins share a placenta, there may be an imbalance of blood supply between the fetuses.
  • Intrahepatic cholestasis of pregnancy (ICP): This liver disorder may cause bile to build up in the body. ICP may lead to premature birth and can cause stillbirth.

Substances such as alcohol and legal and illegal drugs pass through the placenta easily and can cause severe health complications to the fetus, some of which may be life threatening.

This may result in premature birth or a complication that requires a doctor to induce labor early.

Certain abnormalities in the uterus or cervix may increase the risk of premature birth. These include:

  • Having an unusually shaped uterus: If a pregnant person has an unusually shaped womb, such as a unicornuate uterus with one fallopian tube, they may be at increased risk of premature birth.
  • Cervical insufficiency: A cervix may weaken and become unable to hold the fetus, which can result in premature birth.
  • Placenta previa: With this condition, the placenta obstructs the cervix, which can lead to hemorrhage. Placenta previa can be life threatening for the parent and fetus and may require a doctor to induce a preterm birth.

In many cases, doctors and scientists do not know why premature birth occurs.

A complex combination of biological, medical, and psychosocial factors may contribute to the occurrence and cause a spontaneous premature birth.

Various risk factors may contribute to the likelihood of premature birth. These include:

  • Maternal age: People younger than 18 and older than 35 are at higher risk of giving birth prematurely.
  • Income: People living in a low income setting or household are more likely to experience premature birth.
  • Stress: Stress may lead to health complications such as high blood pressure, which may contribute to premature birth.
  • Ethnicity and race: African American, Alaskan Native, and American Indian pregnant people are more likely than white or Hispanic pregnant people to give birth prematurely. This may be due to certain socioeconomic factors, such as the below.
  • Socioeconomic and environmental factors: These may include:
    • domestic violence, including physical, sexual, or emotional abuse
    • lack of social support
    • long working hours with long periods of standing
    • exposure to environmental pollutants that may be harmful to health

Learn more about health inequity.

The Centers for Disease Control and Prevention (CDC) point out that preventing preterm birth remains challenging because the causes are complex and poorly understood.

These include socioeconomic factors that can contribute to racial and ethnic disparities in preterm birth rates.

However, a person may be able to take steps to help prevent premature birth in some cases by:

There are various potential causes of premature birth. Doctors and scientists often do not know why premature birth occurs.

However, contributing factors may include chronic health conditions, multiple pregnancies, and pregnancy complications. Risk factors include factors such as age, ethnicity, and other socioeconomic factors.

Regular contact with health professionals and a healthy lifestyle may help prevent premature birth.

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