Preterm birth is the most common pregnancy complication, affecting around one in ten pregnancies. With innovative new technologies and a growing body of pregnancy care knowledge, it is now possible to understand your individual risk of preterm labor, allowing your doctor to help you delay labor and prevent premature birth or reduce the likelihood of complications if you do need to deliver early.
How important is preterm birth prevention?
Definition of preterm birth
Preterm birth–also known as premature birth–occurs when a baby is born three or more weeks early, or before week 37 of pregnancy. If a birth occurs between 32 and 37 weeks, it is considered a moderate to late preterm birth. Babies born between 28 and 31 weeks are considered very preterm, and those born earlier than 28 weeks are considered to be extremely preterm.
You can learn more about the worldwide problem of preterm birth in this World Health Organization Fact Sheet.
Complications of preterm birth
Not all premature infants face complications, but those born earlier tend to experience more severe issues than those born closer to term. While advanced medical knowledge allows premature babies to receive the best care possible, there is no doubt that the best place for a growing baby to develop is in the mother’s womb. Premature infants face increased risks of mortality and illness as newborns and throughout life.
Use our fetal development tracker to explore your baby’s important new developmental milestones in the womb, week by week.
What triggers preterm labor?
Risk factors for premature birth
While many advances have occurred in understanding the conditions that lead to preterm labor, the causes of preterm delivery are still not fully understood, and preterm labor often happens without any known cause. There are several known risk factors, however. These include medical and nonmedical (lifestyle) risk factors.
Medical risk factors for preterm birth:
- Previous miscarriage
- Maternal age (17 or younger, 35 or older)
- Pregnancy with twins, triplets, or other multiples
- Family history of premature birth (sister, mother, or grandmother)
- Problems with the uterus, placenta, or cervix
- Pregnant through in vitro fertilization (IVF)
- Maternal pre-pregnancy weight (underweight or overweight before pregnancy)
Lifestyle risk factors:
- Alcohol use
- High stress levels
Causes of premature labor
The onset of preterm labor can be spontaneous (occurring on its own) or induced medically by a physician to avoid serious problems for the mother or baby. Though many cases of spontaneous preterm labor occur without any warning, there are several known causes.
- Infection. Infections have been found to be the most common cause of early preterm labor (before 32 weeks). Infections can be in the cervix, uterus, gastrointestinal tract, or even in the mouth, as periodontal disease has been linked to early labor. Infections cause inflammation, which lead to the release of prostaglandins, which can trigger labor.
- Maternal health conditions. Issues such as gestational diabetes, preeclampsia, placenta previa, and placental abruption can cause the onset of early labor.
- Severe stress. Extreme stress–like the kind experienced during a traumatic event–can cause a pregnant mother to release hormones that cause preterm labor.
- Physical exhaustion. Severe physical exhaustion, like the kind occurring in very demanding occupations, can cause the onset of early labor in many women.
- Dehydration. Insufficient fluid intake has been linked to the start of premature contractions.
Can we prevent premature birth?
In some cases, premature birth can be prevented. In other cases, it can’t be prevented, but doctors can provide therapies that allow the fetus to mature more quickly in order to have a healthier start in life in case it needs to be born early. If you and your doctor know that you are at an increased risk of early delivery, there is a greater chance of preventing early labor and improving pregnancy outcomes.
A review of scientific reports on preventing premature birth
A recent Cochrane database review examined 83 medical studies to summarize the benefit of a variety of interventions aimed at preventing spontaneous preterm birth.
They found that the following interventions had clear evidence of benefit in lowering preterm birth rates:
- Midwife-led continuity models of care (where a midwife is the lead medical professional in pregnancy care, in consultation with other medical professionals)
- Screening for lower genital tract infections while pregnant
- Zinc supplementation for pregnant women without systemic illness
- Cerclage (an intervention to surgically reinforce the cervix) for singleton high risk pregnancies
They also found that several interventions were associated with possible benefit:
- Group pregnancy care (vs. standard individual care)
- Antibiotics for asymptomatic infections
- Pharmacological interventions for stopping smoking
- Vitamin D supplementation while pregnant
What tests are available for preterm birth prevention?
Knowing your risk for going into preterm labor is a key piece of information your healthcare provider can use to develop an individualized care plan for your pregnancy. Until recently, the tests available to doctors to predict a mother’s risk of going into early labor have been limited in being able to identify high-risk pregnancies early enough to improve outcomes. A new blood test is now available to predict an individual pregnancy’s elevated risk of preterm delivery.
Previous history of preterm birth
Women with a prior history of spontaneous premature birth have a 2.5-fold risk of early delivery in subsequent pregnancies. So, if you have previously delivered early, you will be considered to be at high risk for another early preterm birth. However, the limitation is that four out of ten pregnancies are in women who have never been pregnant before. As a result, the risk factor of previous preterm birth can only identify about 11% of singleton pregnancies that deliver prematurely.
Cervical length screening
Having a short cervix is a known risk factor for preterm labor. When the cervix is shorter than normal, it is more likely to open sooner and lead to premature labor. Your doctor will take a vaginal ultrasound at around 18-20 weeks to measure the length of your cervix and check for any abnormalities that may indicate that your pregnancy is at an increased risk of ending in preterm birth. Although this ultrasound is an important part of prenatal care, cervical length screening is only able to detect an additional 6% of pregnancies that deliver prematurely.
The PreTRM Test for risk management
The PreTRM Test is a simple blood test that your doctor can order during weeks 18 through 20 of your pregnancy. The test measures the levels of certain proteins circulating in your blood that have been shown to predict an individual level of risk of preterm birth. The results sent to your doctor include an “individual risk prediction” of having your baby too early. The percentage in the report represents how high your pregnancy’s risk of delivering early is, compared to the average risk for women who are pregnant with a single baby. PreTRM is available to pregnant women who are:
- Aged 18 years or older
- Pregnant with a single baby that has no confirmed or expected condition associated with preterm birth
- Not currently showing signs of preterm labor
- Not on progesterone therapy after the first trimester (pregnancy week 1 – week 12)
When your healthcare provider receives the PreTRM risk report, they can work with you to make any changes needed to your pregnancy care plan in order to prevent preterm birth and lower your baby’s risk of complications.
To learn more about the PreTRM Test, read PreTRM FAQs for Moms.
How early in pregnancy can you know your risk of delivering early?
- History of previous preterm birth. If you have had a preterm birth in a previous pregnancy, your doctor will know at the start of your pregnancy that you are at higher risk of delivering early.
- Cervical length screening. A transvaginal ultrasound to measure cervical length is typically performed between weeks 18 and 20.
- The PreTRM Test for risk stratification. The PreTRM Test is performed during weeks 18 through 20, with results sent to your doctor within 7-10 days of your sample arriving at the laboratory.
Strategies for How to Prevent Preterm Labor and Maximize Maternal Health
The most important way to prevent a preterm pregnancy is to make sure you follow guidelines for a healthy pregnancy. Follow your doctor’s advice and check out reputable sources of pregnancy information, such as the National Institute of Child Health and Human Development. Many of the factors that contribute to an overall healthy pregnancy also help lower your risk of preterm labor.
Some key recommendations on a healthy pregnancy include:
- Avoiding tobacco, alcohol, and drugs
- Following a healthy diet
- Taking prenatal vitamins, including the recommended amount of folic acid
- Gaining the recommended amount of weight
- Avoiding infections
- Reducing daily stress and learning how to manage stressful situations
- Drinking plenty of fluids for the prevention of dehydration
- Staying active (unless your doctor advises against it)
- Managing any chronic health conditions, keeping hypertension, diabetes and other chronic conditions under control
- Sharing your medication and supplement list with your doctor (some are unsafe to use during pregnancy)
- Taking care of your teeth, including regular dental checkups for oral health
- Knowing the signs and symptoms of preterm labor and contacting your healthcare provider immediately if you think you are in labor
How can I prevent early labor and reduce my baby’s risk of complications?
If you are found to be at risk of preterm labor, there are several strategies that have been shown to offer high-risk women better chances at extending pregnancy, delivering a healthy baby and avoiding complications. You will need to discuss these treatments with your physician.
Treatments to prevent or delay preterm labor
Progesterone is a hormone that helps the uterus grow and prevents contractions. There are two types of progesterone that are used to prevent preterm labor. If you have had a preterm birth in the past, your doctor may prescribe progesterone injections to prevent another preterm birth. If you have been found to have a short cervix through vaginal ultrasound, you may be prescribed vaginal progesterone. The March of Dimes has additional information about the use of progesterone in the prevention of preterm labor.
If you are found to have cervical insufficiency, your healthcare provider may recommend a cervical cerclage, a procedure where a stitch is placed in the cervix to keep it from opening too early and starting labor.
If you are found to have an infection, the use of antibiotics can reduce the risk of preterm labor and increase general health.
Bed rest has been a commonly prescribed intervention for women at increased risk of early labor; however, research has not found it to provide clear benefits in preventing preterm birth.
If preterm labor begins, your healthcare provider will likely prescribe a tocolytic drug to delay labor and allow time for you to receive important therapies that can speed up your baby’s development. Tocolytics slow or stop uterine contractions. There are several classes of drugs used as tocolytics, including:
- Beta-2 agonists (like terbutaline)
- Prostaglandin inhibitors (like indomethacin)
- Calcium channel blockers (like nifedipine)
- Oxytocin receptor blockers (like atosiban)
There is no commonly used first-line tocolytic, as each class has a different mechanism of action and side effects. Your medical team will assess your condition and choose the most appropriate therapy for you.
Treatments to reduce the risk of preterm labor complications
If you are found to be at risk of delivering within 7 days, your doctor will recommend a course of corticosteroids to help speed up the development of your baby’s lungs, digestive system, and brain. Research has shown that corticosteroids are the best option for improving newborn baby outcomes in the case of preterm birth.
For women found to be at risk of delivering your baby within 24 hours, your doctor may administer magnesium sulfate, a neuroprotective agent that can help reduce your baby’s risk of cerebral palsy and movement problems.
You can learn more about recommendations on the use of magnesium sulfate and other treatments in this article in the journal American Family Physician.
The American College of Obstetricians and Gynecologists has a helpful FAQ sheet for pregnant women where you can learn more about the treatments for managing preterm labor and preparing a developing baby for possible preterm birth.
Preterm birth is a common pregnancy complication. While experts are still working to find the best ways to prevent it, you have the power to make a difference in your pregnancy outcome: maintain a healthy pregnancy, be alert to risk factors for early labor, and work with your healthcare provider to understand your individual risk of preterm birth. Learn more about premature birth.
Talk to your doctor today about the PreTRM Test for your individual risk assessment.