Buy the Book PDA Download

Update Me E-mail alerts The Merck Manual Minute

Print This Topic Email This Topic

Labor (contractions resulting in cervical change) that begins before 37 wk gestation is considered preterm. Risk factors include premature rupture of membranes, infection, cervical incompetence, prior preterm birth, multifetal pregnancy, and placental abnormalities. Diagnosis is clinical. Causes are identified and treated if possible. Management typically includes bed rest, tocolytics (if labor persists), and corticosteroids (if gestational age is < 34 wk). Antistreptococcal antibiotics are given pending negative anovaginal culture results.

Preterm labor may be triggered by premature rupture of membranes, chorioamnionitis (see Abnormalities of Pregnancy: Chorioamnionitis), or another ascending uterine infection; group B streptococci are a common cause of such infections. Preterm labor may also be due to multifetal pregnancy, fetal or placental abnormalities, uterine abnormalities, pyelonephritis, or some sexually transmitted diseases; a cause may not be evident. Prior preterm delivery and cervical incompetence also increase the risk.

Cervical cultures are done to check for causes suggested by clinical findings. Anovaginal cultures for group B streptococci are done, and prophylaxis is appropriately initiated. Most women with a presumptive diagnosis of preterm labor do not progress to delivery.

Treatment

• Antibiotics for group B streptococci, pending anovaginal culture results
• Tocolytics
• Corticosteroids if < 34 wk

Bed rest and hydration are commonly used initially.

Antibiotics effective against group B streptococci are given pending negative anovaginal cultures. Choices include the following:

• For women without penicillin allergy: Penicillin G Some Trade Names
  BICILLIN
  WYCILLIN
  Click for Drug Monograph
  5 million units IV followed by 2.5 million units q 4 h or ampicillin Some Trade Names
  OMNIPEN
  PRINCIPEN
  Click for Drug Monograph
  2 g IV followed by 1 g q 4 h
• For women with penicillin allergy but a low risk of anaphylaxis (eg, maculopapular rash with prior use): Cefazolin Some Trade Names
  ANCEF
  KEFZOL
  Click for Drug Monograph
  2 g IV followed by 1 g q 8 h
• For women with penicillin allergy but an increased risk of anaphylaxis (eg, bronchospasm, angioneurotic edema, or hypotension with prior use, particularly within 30 min of exposure): Clindamycin Some Trade Names
  CLEOCIN
  Click for Drug Monograph
  900 mg IV q 8 h or erythromycin Some Trade Names
  ERY-TAB
  ERYTHROCIN
  Click for Drug Monograph
  500 mg IV q 6 h if anovaginal cultures show susceptibility; if cultures document resistance or results are unavailable, vancomycin Some Trade Names
  VANCOCIN
  Click for Drug Monograph
  1 g IV q 12 h

If the cervix dilates, tocolytics (drugs that stop uterine contractions) can usually delay labor for at least 48 h so that corticosteroids can be given to reduce risks to the fetus. Tocolytics include Mg sulfate, β-adrenergic agonists (eg, terbutaline Some Trade Names
BRETHINE
BRICANYL
Click for Drug Monograph
), Ca channel blockers, and prostaglandin inhibitors. No tocolytic is clearly the first-line choice; choice should be individualized to minimize adverse effects. Mg sulfate is commonly used and is typically well tolerated (see Abnormalities of Pregnancy: Treatment). Prostaglandin inhibitors may cause transient oligohydramnios. They are contraindicated after 32 wk gestation because they may cause premature narrowing or closure of the ductus arteriosus.

If the fetus is < 34 wk, women are given corticosteroids: betamethasone Some Trade Names
CELESTONE
DIPROLENE
LUXIQ
MAXIVATE
VALISONE
Click for Drug Monograph
12 mg IM q 24 h for 2 doses or dexamethasone Some Trade Names
DECADRON
DEXASONE
HEXADROL
Click for Drug Monograph
6 mg IM q 12 h for 4 doses unless delivery is imminent. These corticosteroids accelerate maturation of fetal lungs and decrease risk of neonatal respiratory distress syndrome, intracranial bleeding, and mortality.

A progestin may be recommended in future pregnancies for women who have a preterm delivery to reduce the risk of recurrence.

Last full review/revision December 2008 by Julie S. Moldenhauer, MD

Content last modified December 2008