What causes a premature birth?

Premature birth, or preterm birth, is a complex condition with multiple potential causes and risk factors. Here are some of the key factors associated with premature birth:

Spontaneous Preterm Labor and Birth

• Often, the cause of spontaneous preterm labor and birth is unknown. However, it can result from various factors such as infections, inflammation, or other pregnancy complications34.

Medical Conditions

• Infections: Urinary tract infections, sexually transmitted infections, intraamniotic infections (e.g., chorioamnionitis), and bacterial vaginosis can increase the risk of preterm birth145.
• Chronic Conditions: Conditions like diabetes, high blood pressure, kidney disease, and preeclampsia can lead to preterm birth125.
• Multiple Pregnancy: Being pregnant with twins, triplets, or more increases the risk of preterm birth125.

Previous Pregnancy History

• A history of previous preterm birth is a significant risk factor for subsequent preterm births. The more premature deliveries a woman has had, and the earlier the babies were born, the higher the risk becomes134.

Current Pregnancy Factors

• Short Cervix: Having a short cervix or if the cervix shortens during the second trimester can increase the risk of preterm birth1.
• Placenta Previa and Placental Abruption: These conditions, where the placenta attaches to the wrong part of the uterus or detaches from the uterus before delivery, can lead to preterm birth1.
• Polyhydramnios: Too much amniotic fluid can slightly increase the risk of pregnancy complications, including premature birth4.

Behavioral and Lifestyle Factors

• Smoking and Substance Use: Cigarette smoking, alcohol use, and illicit drug use are associated with an increased risk of preterm birth15.
• Nutritional Factors: Undernutrition, gaining too little or too much weight during pregnancy, and poor dietary habits can also contribute to the risk14.

Demographic and Social Factors

• Age: Women under 18 or over 35 years old are at increased risk15.
• Socioeconomic Status: Women with lower incomes, those experiencing stress, and those lacking social support are at higher risk15.
• Ethnicity: Certain ethnic groups, such as Black women, Native Hawaiian and Pacific Islander women, and American Indian or Alaska Native women, have higher rates of preterm birth5.

Other Factors

• Assisted Reproductive Technologies: Use of technologies like in vitro fertilization in the current pregnancy can increase the risk1.
• Short Time Interval Between Pregnancies: Having less than 6 months between pregnancies can also be a risk factor1.
• Psychological or Social Stress: Severe stress or depression during pregnancy, often accompanied by related issues like lack of social support, emotional abuse, or domestic violence, may be linked to premature birth4.

In many cases, despite these risk factors, the exact cause of preterm birth remains unknown, highlighting the need for continued research to understand the mechanisms and causes of preterm birth234.