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For further information, see CMDT Part 19-13: Preterm Labor

Key Features

  • Preterm birth defined as birth between 20 0/7 and 36 6/7 weeks' gestation

  • Spontaneous preterm labor responsible for at least two-thirds of preterm births

  • Preterm, regular, rhythmic contractions 5 minutes apart

  • Cervical dilatation, effacement, or both occur

  • Most common reason for antepartum hospitalization

Clinical Findings

  • Current cusp of viability is 23–25 weeks' gestation; infants born prior to 23 weeks rarely survive

  • Rates of infant death and long-term neurologic impairment are inversely related to gestational age at birth

  • About two-thirds of the preterm births are "late preterm births", which occur between 34 0/7 weeks and 36 6/7 weeks; good outcomes are expected for "late preterm births"

  • Major risk factors for spontaneous preterm labor include

    • A past history of preterm birth

    • A short cervical length as measured by transvaginal ultrasound

  • Other known risk factors are many but include

    • Black race

    • Multiple gestation

    • Intrauterine infection

    • Substance abuse

    • Smoking

    • Periodontal disease

    • Socioeconomic deprivation

    • Numerous preterm births are preceded by ruptured membranes


  • Fetal fibronectin measurement in cervicovaginal specimens can differentiate true from false labor

  • A level < 50 ng/mL has a negative predictive value of 93–97% for delivery in 7–14 days among women with a history of preterm delivery currently having contractions

  • However, fetal fibronectin is not recommended as a screening test in asymptomatic women because of its low sensitivity


  • Limited activity and bed rest

    • Frequently recommended despite the fact that evidence has failed to demonstrate improved outcomes in these women

    • Additionally, and paradoxically, such recommendations may place a woman at an increased risk to deliver preterm

  • Women in preterm labor should receive antimicrobial prophylaxis against group B streptococcus

  • Corticosteroids

    • A single short-course of corticosteroids should be administered to promote fetal lung maturity when preterm birth is anticipated between 23 and 34 weeks gestation

      • Betamethasone, 12 mg intramuscularly repeated once 24 hours later or

      • Dexamethasone, 6 mg intramuscularly repeated every 12 hours for four doses

    • A single repeat course should be considered in women who are at risk for preterm delivery within the next 7 days, and whose prior dose of antenatal corticosteroids was administered more than 14 days previously

    • Rescue course corticosteroids could be provided as early as 7 days from the prior dose, if indicated by the clinical scenario

    • Administration of betamethasone may be considered in pregnant women between 34 0/7 and 36 6/7 weeks of gestation at imminent risk of preterm birth within 7 days, and who have not received a previous course of antenatal corticosteroids

  • Magnesium sulfate

    • Commonly used but no longer recommended as a first-line agent

    • Might be utilized for women in labor at the prescribed gestational ages for neuroprotection in preterm infants

    • May also be protective against cerebral palsy in infants from 24 weeks' to 32 weeks' gestation when given at ...

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