Preterm Labor

Preterm Labor

Luce A. Kassi

Samantha P. DeAndrade

Audra R. Meadows


Preterm labor is a common cause of hospitalization in pregnancy and may lead to preterm birth. Preterm birth is a significant public health challenge, difficult to predict, and the leading cause of infant morbidity and mortality worldwide.1,2,3,4,5 Preterm birth is a live birth prior to 37 weeks’ gestation. Preterm labor is defined as regular contractions accompanied by cervical dilation of greater than or equal to 3 cm, a short cervix, or cervical change on serial examination between 20 and 36 6/7 weeks of gestation6 (Table 18.1).

The primary management goal is to reduce the incidence of preterm birth and extend pregnancy to achieve a greater gestational age for babies whose premature birth cannot be prevented. Because more than half of pregnant women hospitalized due to preterm labor deliver at term, appropriate diagnosis and selection of candidates for treatment of preterm labor is essential. It is equally important to prevent unnecessary treatment of women who are not in preterm labor.7,8 Patients who deliver preterm are at increased risk for a preterm birth in a subsequent pregnancy.9


Every year, nearly 15 million premature births occur worldwide, with approximately 400,000 preterm births occurring annually in the United States.1,5 Most cases of preterm births occur in the late preterm period (34 to 36 6/7 weeks), followed by births at 28 to 32 weeks, and the least occur at less than 28 weeks of gestation10 (Figure 18.1). Racial and ethnic inequities exist and persist among rates of preterm birth.1 Infants born to mothers of Black race are significantly more likely to be born preterm (Figure 18.2) and die in the first year of life. Presently, preterm birth rates continue to
rise. In 2017, the US preterm birth rate was 9.9%, with increases reported each year for the previous three consecutive years.10

TABLE 18.1 Clinical Criteria for the Diagnosis of Preterm Labor

  • Pregnancy between 20 0/7 and 36 6/7 weeks’ gestation

  • Regular uterine contractions (every 5 min or five in 1 h), PLUS

    • Cervical dilation to ≥3 cm OR

    • Cervical change in dilation and/or effacement on serial cervical examination OR

    • Short cervix or cervical dilation <20 mm (singleton) and <25 mm (twin) on transvaginal ultrasound

Figure 18.1: Preterm birth rates: United States, 2014-2016. (From Martin JA, Osterman MJK. Describing the Increase in Preterm Births in the United States, 2014-2016. NCHS Data Brief, no 312. Hyattsville, MD: National Center for Health Statistics. 2018.

1Significantly increasing linear trend for 2014-2016 (p < 0.05).

2Significant increase from 2014 and 2015 (p < 0.05). Available at

Premature infants are at high risk for neonatal complications, long-term developmental and intellectual disabilities, as well as chronic disease. The risk of long-term complications associated with preterm birth strongly correlates with gestational age.11 Short- and long-term complications include respiratory distress syndrome, intraventricular hemorrhage, necrotizing enterocolitis, neurodevelopmental disability (cerebral palsy), chronic respiratory abnormalities (asthma,
bronchopulmonary dysplasia), infections, poor growth, poor hearing, and vision loss due to retinopathy of prematurity—all resulting in recurrent hospitalizations.2,11

Figure 18.2: Preterm birth rates by race and Hispanic origin of mother: United States, 2014-2016. (From Martin JA and Osterman MJK. Describing the Increase in Preterm Births in the United States, 2014-2016. NCHS Data Brief, no 312. Hyattsville, MD: National Center for Health Statistics. 2018. Available at

Beyond health implications, preterm birth is costly. Care of a healthy, term infant ranges from $5000 to $7000, whereas the average cost of care for a preterm infant is roughly $50,000 to $80,000, with costs increasing as gestational age at birth decreases.12 An Institute of Medicine report estimates medical and societal costs of preterm birth in the United States to be $26.2 billion annually due to hospitalizations and ongoing medical care for mother and baby (to age 5), social services, and lost wages in the workforce; $16.9 billion for healthcare costs alone.2 A March of Dimes report estimates that health plans spend $12.7 billion annually due to preterm birth.13 Another study found that preterm birth cost employer-sponsored health plans in the United States $6 billion more for preterm infants compared to term infants.12 These studies approach cost estimates differently yet what is clear is the great expense of preterm newborn care.


The recognition of women at increased risk for preterm birth as well as women experiencing preterm labor provides an opportunity for emergency medicine practitioners to prevent a preterm birth and extend pregnancy by intervening clinically. Healthcare providers in the emergency department (ED) may be the first point of contact between a patient experiencing preterm labor and the healthcare system. As such, it is important for emergency practitioners to (1) recognize signs and symptoms of preterm labor, (2) treat to extend pregnancy and improve neonatal outcomes, and (3) refer to appropriate perinatal care facilities when needed.

Transfer may be necessary in order to match the hospital level to the maternal and neonatal care needed. The available staff and resources impact both perinatal morbidity and mortality.14 Levels of maternal and neonatal care have separate classification systems. The levels range from Levels I to IV for maternal perinatal centers and Levels I to IV for neonatal perinatal centers as described by the American College of Obstetricians and Gynecologists (ACOG), the Society for Maternal-Fetal Medicine (SMFM), and the American Academy of Pediatrics (AAP).14,15 These tiered systems for maternal and neonatal levels are described in Table 18.2. The centers at the highest level have systems capabilities, staff, and equipment to appropriately manage higher acuity patients. The highest-level centers support the facilities across all the tier levels. Hospitals participate in a regionalized system of perinatal care to direct patient transfers. Emergency medicine providers need to be aware of this system as well as the maternal and neonatal resources at their institutions in order to triage patients appropriately.

Dec 30, 2020 | Posted by in EMERGENCY MEDICINE | Comments Off on Preterm Labor
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