Risk Factors for Preterm Birth. What risk factors do you have for premature birth?

The specific causes of spontaneous preterm birth are not fully understood. However, there are several known risk factors for preterm birth.

While it is important to track these risk factors in every pregnancy, up to half of women who deliver prematurely have no known risk factors.¹

Known Risk Factors for Preterm Labor

Medical risk factors for premature birth:*

• Prior miscarriage
• Pregnancy with multiples
• Family history of premature birth (sister, mother, or grandmother)
• Maternal age (17 or younger, 35 or older)
• Problems with uterus, placenta, or cervix (including short cervix length)
• Pregnant through in vitro fertilization (IVF)
• Maternal weight (underweight or overweight before pregnancy)

Lifestyle risk factors for preterm birth:*

• High stress levels
• Smoking
• Alcohol use

*This is not a comprehensive list or a recommendation of all risk factors that clinicians should use to determine a patient’s risk for preterm birth.

Standard Methods: Predicting Preterm Birth Risk

Although breakthroughs in obstetrics and neonatal care have vastly improved the odds of healthy survival for mothers and infants, methods for assessing the risk for spontaneous preterm birth have not advanced as quickly. Until recently the primary tools for assessing this risk of spontaneous birth have included the pregnant woman’s history of preterm birth and measurements of cervical length. Even with these tools, most cases of premature birth were “hiding in plain sight”, not apparent until too late to change the clinical course. 

Prior History of Preterm Birth

In clinical studies, a history of previous preterm birth identified 11% of future preterm births. ^2,3

Short Cervical Length

The use of vaginal ultrasound to measure cervical length during pregnancy is used as a screening measure to assess the risk of preterm birth. However, cervical length screening detects only an additional 6% of singleton pregnancies that deliver prematurely. ^4,5

A New Approach: Predicting Preterm Birth Risk

Improved spontaneous preterm birth risk prediction means a better chance for physicians and patients to work together to make clinical decisions to extend gestation time and provide better pregnancy outcomes. 

Recently, scientists discovered that key proteins, measured in the blood of pregnant women, were powerful predictors of a higher risk of sPTB. 

Based on this discovery, Sera developed the PreTRM Test, the first broadly clinically validated blood test to provide early risk stratification for spontaneous preterm birth in singleton pregnancies in women with no known risk factors. The PreTRM Test provides early, accurate, individualized risk information to help patients and physicians make more informed healthcare decisions. 

Learn more about the PreTRM test

FAQs about Premature Birth Risk Factors

What is the most modifiable risk factor for preterm labor?

Among the modifiable risk factors for preterm labor, maternal smoking stands out as one of the most significant contributors. Numerous pregnancy studies and clinical research, including a research article published in the Journal of Obstetrics and Gynaecology Canada (2019), have consistently highlighted the detrimental effects of smoking on pregnancy outcomes. Smoking during pregnancy exposes the fetus to harmful chemicals and toxins, leading to placental dysfunction, reduced oxygen supply, and heightened inflammation, all of which increase the risk of preterm delivery. Fortunately, this risk factor is entirely modifiable through smoking

cessation interventions and support programs. Expectant mothers who quit smoking early in pregnancy can significantly reduce their chances of premature birth, ensuring a healthier start for both themselves and their babies. This underscores the critical importance of smoking cessation efforts in prenatal care to mitigate the risk of preterm birth and long term effects on babies.

What are the most common concerns during pregnancy?

Pregnancy is a transformative and complex period in a woman’s life, often accompanied by various common concerns that require careful monitoring and management. According to the American College of Obstetricians and Gynecologists (ACOG), some of the most prevalent concerns during pregnancy include gestational diabetes, preeclampsia, and premature birth.

Gestational diabetes, which affects approximately 6-9% of pregnancies, involves elevated blood sugar levels and requires dietary adjustments and possibly medication to control.

Preeclampsia, characterized by high blood pressure and organ damage, can pose serious risks to both the mother and baby, necessitating close medical supervision during pregnancy.

Additionally, preterm labor, labor that occurs before 37 weeks, is a concern due to its potential adverse outcomes for baby. Beyond these, expectant mothers may also experience common discomforts such as nausea, back pain, and fatigue. These concerns underscore the importance of regular prenatal care and communication with healthcare providers to address and manage these issues effectively, ensuring a healthier pregnancy journey.

Does bed rest prevent preterm labor?

The idea of bed rest as a preventive measure for preterm labor has been a subject of debate and research within the medical community. However, contemporary medical evidence suggests that bed rest may not be an effective strategy for preventing premature birth. The American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine have both issued statements indicating that bed rest is not recommended for preventing preterm birth, as it has not demonstrated consistent benefits and may even lead to adverse effects such as muscle atrophy and increased risk of blood clots.

A systematic review published in the Journal of Obstetrics and Gynaecology Canada (2018) further supports this stance, finding that bed rest does not significantly reduce the risk of preterm birth. Instead, healthcare providers focus on other evidence-based interventions, such as progesterone therapy for high-risk pregnancies, which have shown more promise in preventing preterm labor. It is essential for expectant mothers to consult with their healthcare providers to determine the most appropriate and evidence-based strategies for their specific pregnancy circumstances, rather than relying on bed rest as a preventive measure.

Who has the highest rate of preterm birth?

The highest rates of preterm birth are often observed among certain demographic groups and in specific regions, highlighting disparities in maternal and infant health. According to data from the Centers for Disease Control and Prevention (CDC), preterm birth rates are notably higher among Black women in the United States. In 2019, the preterm birth rate for Black women was 14.4%, significantly higher than the national average of 10.2%. This disparity is a complex issue influenced by various social, economic, and healthcare factors, including limited access to quality prenatal care and higher rates of chronic stress.

Moreover, geographic disparities also exist, with some regions experiencing higher rates of preterm birth than others. For instance, the southeastern United States often reports higher rates of preterm birth compared to the national average. Addressing these disparities requires comprehensive efforts to improve healthcare access, reduce maternal stress, and promote overall maternal well-being, underscoring the importance of equitable healthcare policies and interventions.

Research and References

1. Iams, JD, et al. Prevention of preterm parturition. N Engl J Med. 2014;370:254-61.
2. Petrini JR, et al. Estimated effect of 17 alpha-hydroxyprogesterone caproate on preterm birth in the United States. Obstet Gynecol. 2005;105:267-72.
3. Martin JA, et al. Births: Final Data for 2002. Natl Vital Stat Rep. 2003; 52(10):1-113.
4. Hassan SS, et al. Vaginal progesterone reduces the rate of preterm birth in women with a sonographic short cervix: a multicenter, randomized, double-blind, placebo-controlled trial. Ultrasound Obstet Gynecol. 2011;38:18-31.
5.  Martin JA, et al. Births: Final Data for 2009. Natl Vital Stat Rep. 2011; 60(1):1-70.