Labor, Preterm

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

  • Multifetal 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

• Overall, evidence supports the use of first-line tocolytic treatment with beta-adrenergic receptor agonists, calcium channel blockers, or indomethacin for short-term prolongation of pregnancy (up to 48 hours) to allow for the administration of antenatal corticosteroids

• Terbutaline

  • Can be given as an intravenous infusion starting at 2.5 mcg /min or as a subcutaneous injection starting at 250 mcg given every 30 minutes

  • Oral administration is not recommended because of the lack of proven efficacy and concerns about maternal safety

  • Serious maternal side effects include

    • Tachycardia

    • Pulmonary edema

    • Arrhythmias

    • Metabolic derangements (such as hyperglycemia and hypokalemia)

    • Death

  • Because of these safety concerns, the US Food and Drug Administration warns that terbutaline be administered exclusively in a hospital setting and discontinued after 48–72 hours of treatment

• Nifedipine, 20 mg orally every 6 hours, and indomethacin, 50 mg orally once then 25 mg ...