The Effects of Spontaneous Preterm Birth and Preterm Labor

What is preterm birth?

A baby’s birth is considered to be preterm (or premature) if they are born before the start of the 37^th week of pregnancy—or three or more weeks before the baby’s due date. In general, the earlier the birth, the bigger the impact of preterm birth on the baby’s health. Most preterm births happen spontaneously with little or no warning signs.

Types of preterm deliveries

Premature labor can start on its own—known as spontaneous preterm birth—or because of a medical intervention–known as medically indicated preterm birth. Some health reasons why a doctor may induce labor or perform a cesarean section to deliver a preterm infant include:

• Preeclampsia. A pregnancy complication characterized by high blood pressure in the patient.
• Placental abruption. A condition where the placenta separates from the lining of the uterus endangering the health of the baby.
• Fetal distress. A complication in which the baby does not receive enough oxygen or nutrients or is experiencing other forms of stress.
• Intrauterine growth restriction. A condition where the baby does not grow as quickly as expected.

Classification of preterm birth by gestational age

There are several classes of prematurity, based on the gestational age of the premature infants (or how many weeks the pregnancy lasted). Because the health needs of preemies tend to correspond with how early they are born, researchers who study preterm birth have created three main groups based on how long the pregnancy lasted. These categories are:

• Moderate or late preterm: premature birth between 32 and 37 weeks
• Very preterm: premature birth between 28 and 32 weeks
• Extremely preterm: premature birth before 28 weeks

While no two premature babies are exactly alike in their health challenges and needs, these categories help doctors and parents understand the types of issues a baby may face, based on how early they arrive. Because babies born earlier tend to spend more time in the hospital, earlier preterm births can also have a more significant emotional and economic effect on parents than births that happen closer to the due date. The spontaneous nature of these preterm births makes preparation very difficult as well.

How common is preterm birth?

In 2020, there were just over 3.6 million babies born in the United States. Of these, 10.09%—or about 364,000—were born prematurely.¹ Preterm birth is the most prevalent medical challenge facing pregnant mothers in the US. With one in ten pregnancies affected by preterm birth, it is more common than other well-known pregnancy outcomes like preeclampsia, Down syndrome, and cystic fibrosis.

Are some women more prone to preterm labor?

Doctors and researchers have made great strides in understanding preterm birth, but the exact causes of spontaneous preterm birth—and the reasons that some mothers go into labor early—are not yet fully understood. 

While preterm birth is idiopathic, which means that it arises spontaneously and has generally unknown causes, there are several risk factors that are known to increase the chances of spontaneous preterm birth. Some of these include:

• Previous preterm birth: If you have had a spontaneous preterm birth before, your risk of having another one is higher.
• Family history of preterm birth. If your mother, sister, or grandmother had a preterm delivery, obstetric data shows your chances of preterm birth may be higher.
• Pregnancy with twins, triplets, or more: Carrying more than one baby at a time increases the risk of preterm birth.
• Maternal age. Mothers who are 17 or younger, or 35 or older, have higher risk of spontaneous preterm birth than other pregnant women.
• Maternal weight. Women who are underweight or overweight before pregnancy have an increased risk of premature labor.
• Certain medical issues: Chronic health conditions like diabetes, high blood pressure, and infections can increase a mom’s risk of preterm birth.
• Substance use: Smoking, alcohol consumption, and illicit drug use during pregnancy can increase the risk of preterm birth.
• Late or no prenatal care: Women who don’t receive appropriate health care during pregnancy are at higher risk of preterm birth.
• Short cervical length: A short cervix is associated with an increased risk of preterm birth. (For more about the cervix and its role in pregnancy, see our recent blog post).
• Stress: High levels of stress during pregnancy have an adverse effect on health and have been linked to an increased risk of preterm birth.

Many cases of preterm birth occur without any known health risk factors, and not all women with risk factors will experience preterm labor. It’s important to discuss your health and medical history with your health care provider as early as possible in your pregnancy. The American Pregnancy Association has a fact sheet on premature labor that includes a detailed list of risk factors.

Symptoms of spontaneous preterm labor

Whether or not you have any known risk factors for preterm birth, it’s very important to learn the signs and symptoms that may indicate that labor has begun. These include:

• Contractions every 12 minutes or more often
• Change in vaginal discharge
• Pelvic pressure
• Backache
• Cramps
• Water breaking

If you have any of these symptoms, call your doctor immediately. They may be able to give you treatments that can delay labor and/or improve your chances of a safe and healthy delivery. To learn more about the symptoms of spontaneous preterm birth, read this health action sheet from the March of Dimes.

Effects of spontaneous preterm birth on infants

Preterm birth is associated with health problems that can impact babies at birth and throughout their lives. Sadly, preterm birth is a leading cause of infant mortality and morbidity.

Survival 

Premature birth is one of the most common causes of newborn death. In the United States, prematurity accounts for about one third of all infant deaths. Thankfully, medical advances mean that more preemies are able to survive today than ever before. Most of the babies who do not survive are born extremely preterm, and each week a baby can stay in the womb helps improve their chances of survival and decrease their chances of long-term health problems. 

You can learn more about the important developments that happen during each week of pregnancy here.

Health problems

During a typical 40-week pregnancy, babies undergo important growth and development in the final weeks. Babies who are born too early may have certain health issues related to not being able to finish developing in the womb. These problems can be found in the heart, lungs, brain, and digestive system, among others. These health issues are often more severe in babies born extremely early.

Our recent blog post, on preemie health challenges and other characteristics of premature babies has more information.

Short term health problems for preemies

Many of the health problems faced by premature babies are short term problems that can be managed in the hospital. These include: 

• Breathing problems like respiratory distress syndrome
• Cardiovascular concerns like bradycardia (slower than normal heart rate)
• Gastrointestinal issues like difficulty with feeding
• Metabolic problems like jaundice
• Brain issues like hemorrhage (bleeding)
• Infections like pneumonia
• Vision problems like retinopathy (damage to the retina)

Long term health problems for preemies

Some preterm babies continue to have health issues later in life. Some of the medical issues they may face include:

• Cerebral palsy
• Intellectual disabilities
• Mental health issues
• Chronic lung diseases
• Vision loss
• Hearing loss
• High blood pressure
• Diabetes

These health problems tend to be more severe in babies who are born extremely early.

Mental effects of spontaneous preterm birth on moms

The unique challenges that come with spontaneous preterm birth affect not only babies themselves, but their mothers, fathers, and communities. Having a baby early can have devastating economic and psychological effects on families. For example, mothers who experience a preterm birth are at higher risk for mental health issues like depression and post traumatic stress disorder (PTSD).²

Ashley Randolph recently shared her difficult spontaneous preterm birth story with us. She stresses that all pregnant women need better access to education and support throughout the process of delivering and caring for preterm infants. You can read her full interview on the psychological effects of premature birth.

Preventing preterm birth

With advances in pregnancy care knowledge, some cases of preterm birth can be prevented. In other cases, preterm labor cannot be stopped, but doctors can give specialized care just before birth that can give babies a healthier start in life. If you and your health care provider know that you are at higher risk of early labor, you’ll have a better chance of preventing labor and improving your pregnancy outcomes.

Staying healthy during pregnancy

The most important way to prevent preterm birth and other complications is to stay as healthy as possible during your pregnancy. Be sure to follow your doctor’s advice, including:

• Avoiding alcohol, illicit drugs, and tobacco
• Following a healthy diet
• Taking prenatal vitamins
• Gaining the recommended amount of weight
• Avoiding infections
• Managing stress
• Drinking plenty of fluids
• Keeping chronic conditions under control

If you are researching pregnancy health tips online, be sure to follow reputable sources like the National Institutes of Health and the World Health Organization. And be sure to discuss your healthy pregnancy strategies with your health care provider.

Know your risk factors for spontaneous preterm birth

Knowing your individual risk for preterm birth is important in planning for a healthy pregnancy. If you have known risk factors, like a multiple pregnancy, a short cervix, or a history of a previous preterm birth, your doctor will adjust your care plan accordingly.

If you are pregnant with a single baby and have no clear risk factors for preterm birth, there is also a risk assessment test your doctor can order for you: The PreTRM Test for Risk Management. This is based on a single blood sample taken between weeks 18 through 20 of your pregnancy. PreTRM measures certain proteins in your blood that have been shown to predict an individual risk level for preterm birth. When your health care provider receives the PreTRM risk report, they can work with you to make any changes to your pregnancy care plan to avoid preterm labor and improve your baby’s chances of a healthy birth. 

Learn more about the PreTRM Test.

Preterm birth is an important pregnancy complication, affecting about one in ten pregnancies. It’s important to understand the effects of prematurity on babies and families, and to do all you can to understand your risks, prevent premature labor, and give your baby a great start in life.

What causes spontaneous preterm labor?

In many cases, the causes of spontaneous preterm labor are not known. Several key risk factors for preterm birth include pregnancy with multiple babies, infections, chronic health conditions, and a history of a previous premature delivery.

How common is spontaneous preterm birth?

Preterm birth—when a baby is born before 37 weeks of pregnancy—affects about one in ten pregnancies in the United States.

What is the difference between spontaneous and medically indicated preterm birth?

A preterm birth is spontaneous if the labor began on its own—with cervical dilation, water breaking, or other labor symptoms. A medically indicated preterm birth is one in which labor is induced by a doctor, or a baby is delivered through a cesarean section because of health problems for the mother, the baby, or both.

1. Hamilton BE, et al. Births: Provisional data for 2020. Vital Statistics Rapid Release; no 12. Hyattsville, MD: National Center for Health Statistics. May 2021.
2. Anderson, Cheryl PhD, RN, CNS; Cacola, Priscila PhD. Implications of Preterm Birth for Maternal Mental Health and Infant Development. MCN, The American Journal of Maternal/Child Nursing 42(2):p 108-114, March/April 2017. | DOI: 10.1097