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Key Features

  • Labor beginning before 37th week of pregnancy

  • Preterm, regular, rhythmic contractions 5 minutes apart

  • Cervical dilatation, effacement, or both occur

Clinical Findings

  • 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

Diagnosis

  • 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

Treatment

  • 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

    • 4–6 g intravenous bolus followed by infusion of 2–3 g/h

    • Magnesium levels may be determined every 4–6 hours to monitor for evidence of toxicity

  • Terbutaline (2.5 mcg/min intravenously titrated to a maximum 20 mcg/min or 2.5–5.0 mg orally every 4–6 hours)

  • Oral terbutaline

    • Not recommended because of the lack of proven efficacy and concerns about maternal safety

    • Side effects include tachycardia, pulmonary edema, arrhythmias, metabolic derangements (such as hyperglycemia and hypokalemia), and even death

    • If it is used to treat preterm labor, the FDA recommends this medication be administered exclusively in a hospital setting and be discontinued within 48–72 hours

  • Nifedipine, 20 mg orally every 6 hours, and indomethacin, 50 mg orally once then 25 mg orally every 6 hours up to 48 hours, have also been used with limited success

  • Nifedipine should not be given in conjunction with magnesium sulfate

  • Women with shortened cervices (< 25 mm before 24 weeks gestation) may benefit from placement of a cervical cerclage

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