Pregnancy normally lasts about 40 weeks (a little over 9 months from the first day of the last period). “Preterm birth” is defined as birth before 37 weeks of pregnancy.  

Sometimes, preterm birth can happen on its own. This is called spontaneous preterm birth. Other times, labor is induced (started by medications or other means) or a cesarean delivery is performed early for medical reasons to protect the mother’s or baby’s health. This is called a medically indicated preterm birth.  

Preterm birth has been divided into these categories: 

• Preterm birth: Birth that occurs before 37 weeks of pregnancy 

• Late preterm birth: Birth that occurs between 34 and 36 weeks of pregnancy 

• Early preterm birth: Birth that occurs before 34 weeks of pregnancy 

The earlier a baby is born, the greater the chance of more serious and long-lasting health risks. But even babies born later in the preterm period (between 34 and 36 weeks) can have health problems. Babies born before 22 or 23 weeks have very low survival rates, and if they do survive, are more likely to have lifelong health problems.   

About 1 in 10 babies in the United States is born preterm.  

Infants born preterm are more likely to have health problems, especially in the first year of life. These may include: 

• Trouble with breathing, eating, and keeping warm 

• Infections 

• Cerebral palsy  

• Hearing and vision loss  

• Slower growth and development  

• Behavioral problems and learning difficulties 

The majority of preterm babies need to stay in a neonatal intensive care unit (NICU) to get special medical care. Once they leave the hospital, some babies may still need ongoing care to treat medical issues. Some health problems can last well into childhood.  

The following risk factors have been associated with preterm birth: 

• Preterm birth in a previous pregnancy  

• Lifestyle factors, including smoking, substance use, and low prepregnancy weight  

• Having limited access to resources, including prenatal care, reliable transportation, or a safe living situation  

• Getting pregnant less than 18 months after having a baby  

• Having bacteria in the urine, a condition called bacteriuria, especially if it occurs without causing any symptoms  

• Having a short cervix as measured by ultrasound 

• Pregnancy complications such as preeclampsia, problems with the placenta, and fetal growth restriction.  

•  Fetal genetic conditions 

• Medical conditions that existed before pregnancy, including high blood pressure, diabetes, and lupus 

• Preterm labor (when labor contractions start too early) and preterm premature rupture of membranes (when your water breaks before labor starts and it’s before 37 weeks) 

• Being pregnant with twins, triplets, or more 

Many pregnant people have at least one risk factor for preterm birth. Having a risk factor does not mean that you will have a preterm birth. Some risk factors, like smoking, can be changed. Others, such as having a previous preterm birth, cannot. Extra care during pregnancy may be recommended.  

• Frequent, regular contractions that: 

  • Occur 6 or more times in 1 hour 

  • Cause your belly to tighten and harden and are uncomfortable 

• Lower abdominal cramps or a low backache that gets worse or doesn’t go away 

• A change in vaginal discharge (watery, bloody, or like mucous) or an increase in discharge 

• Pelvic pressure (a feeling that the baby is pushing down) 

• Your water breaks 

• Bleeding with or without abdominal pain 

If you have mild signs or symptoms, contact your healthcare provider right away. If your symptoms are severe or persist, even if they are mild, you should go to the nearest hospital if you can do so safely. If you are worried about your safety or have heavy bleeding, call emergency services (911).

Sometimes preterm labor stops on its own. The management of your symptoms depends on your signs and symptoms, gestational age, and whether your cervix has started to open (dilate) or soften.   

• You will likely be admitted to the hospital. In some cases, you may be transferred to a hospital that specializes in caring for preterm infants.  

• A steroid medication may be given to prepare the fetus’s lungs and other organs for a possible early birth.   

• If you are less than 32 weeks pregnant, another medication called magnesium sulfate may be given to protect the fetal brain and nervous system. This medication may reduce rates of cerebral palsy and death in babies who are born before 32 weeks.    

• Depending on the situation, medications called tocolytics may be given to try to slow down contractions. This may allow time for the steroid injections or magnesium sulfate to take effect or for you to be moved to a hospital with a higher level of care.   

Preterm birth prevention can start even before you become pregnant. Your healthcare provider can help you address any risk factors that could be changed, like stopping smoking, getting better nutrition, or discussing birth control options to help with pregnancy planning. 

During an early prenatal care visit, you will have a test to see if you have bacteria in your urine. The length of your cervix may be measured at the standard ultrasound exam between 18 and 23 weeks of pregnancy. If you are found to have a short cervix, treatment with vaginal progesterone may be recommended. This treatment has been shown to reduce the risk of preterm birth. This medication is also offered to people who have had a prior spontaneous preterm birth. 

In some cases, a procedure called cerclage may be recommended. In this procedure, the patient is taken to the operating room and a stitch is placed around the cervix to hold it closed. It is most often done through the vagina or, less frequently, with laparoscopy through the abdomen. With the abdominal approach, a cesarean delivery is needed. The approach used depends on many factors, such as how far along you are in pregnancy and your personal history of preterm birth or miscarriage.