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Preterm Labor

By

Julie S. Moldenhauer

, MD, Children's Hospital of Philadelphia

Reviewed/Revised Jul 2021 | Modified Sep 2022
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Labor (contractions resulting in cervical change) that begins before 37 weeks gestation is considered preterm. Risk factors include prelabor rupture of membranes, uterine abnormalities, infection, cervical incompetence, prior preterm birth, multifetal pregnancy, and fetal or placental abnormalities. Diagnosis is clinical. Causes are identified and treated if possible. Management typically includes bed rest, tocolytics (if labor persists), corticosteroids (eg, if gestational age is < 34 weeks—see below Corticosteroids Labor (contractions resulting in cervical change) that begins before 37 weeks gestation is considered preterm. Risk factors include prelabor rupture of membranes, uterine abnormalities, infection... read more ) and possibly magnesium sulfate (if gestational age is < 32 weeks). Antistreptococcal antibiotics are given pending negative anovaginal culture results.

Preterm labor may be triggered by

A cause may not be evident.

Diagnosis

  • Clinical evaluation

Diagnosis of preterm labor is based on signs of labor and length of the pregnancy.

Anovaginal cultures for group B streptococci are done, and prophylaxis is appropriately initiated. Urinalysis and urine culture are done to check for cystitis and pyelonephritis. Cervical cultures are done to check for STIs if suggested by clinical findings.

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

  • Sometimes corticosteroids (eg, between 24 and 34 weeks)

  • Consideration of progestin in future pregnancies

Bed rest and hydration are commonly used initially.

Antibiotics

  • For women without penicillin allergy: Penicillin G 5 million units IV followed by 2.5 million units every 4 hours or ampicillin 2 g IV followed by 1 g every 4 hours

  • For women with penicillin allergy but a low risk of anaphylaxis (eg, maculopapular rash with prior use): Cefazolin 2 g IV followed by 1 g every 8 hours

  • For women with penicillin allergy and an increased risk of anaphylaxis (eg, bronchospasm, angioneurotic edema, or hypotension with prior use, particularly within 30 minutes of exposure): Clindamycin 900 mg IV every 8 hours if anovaginal cultures show susceptibility; if cultures document resistance or results are unavailable, vancomycin 20 mg/kg IV every 8 hours (maximum dose of 2 g)

Tocolytics

If the cervix dilates, tocolytics (drugs that stop uterine contractions) can usually delay labor for at least 48 hours so that corticosteroids can be given to reduce risks to the fetus. Tocolytics include

  • Magnesium sulfate

  • A calcium channel blocker

  • Prostaglandin inhibitors

No tocolytic is clearly the first-line choice; choice should be individualized to minimize adverse effects.

IV magnesium sulfate should be considered in pregnancies < 32 weeks. In utero exposure to the drug appears to reduce the risk of severe neurologic dysfunction (eg, due to intraventricular hemorrhage), including cerebral palsy, in neonates.

Prostaglandin inhibitors may cause transient oligohydramnios. They are contraindicated after 32 weeks gestation because they may cause premature narrowing or closure of the ductus arteriosus.

Corticosteroids

If the fetus is ≥ 24 weeks and < 34 weeks, women are given corticosteroids unless delivery is imminent. Another course of corticosteroids can be considered if all of the following are present:

Corticosteroids should also be considered in the following circumstances

One of the following corticosteroids may be used:

  • Betamethasone 12 mg IM every 24 hours for 2 doses

  • Dexamethasone 6 mg IM every 12 hours for 4 doses

These corticosteroids accelerate maturation of fetal lungs and decrease risk of neonatal respiratory distress syndrome, intracranial bleeding, and mortality.

Progestins

A progestin has been recommended in future pregnancies for women who have a preterm delivery to reduce the risk of recurrence. This treatment is initiated during the 2nd trimester and continued until just before delivery.

However, supporting evidence is not definitive. Earlier studies showed meaningful reductions in preterm birth and neonatal morbidity for women who had had a preterm birth and were given 17-alpha-hydroxyprogesterone caproate (17-OHPC; 4 Treatment references Labor (contractions resulting in cervical change) that begins before 37 weeks gestation is considered preterm. Risk factors include prelabor rupture of membranes, uterine abnormalities, infection... read more ). But in a recent international study of women who had had a preterm birth, 17-OHPC was no more effective than placebo (5 Treatment references Labor (contractions resulting in cervical change) that begins before 37 weeks gestation is considered preterm. Risk factors include prelabor rupture of membranes, uterine abnormalities, infection... read more ). These discrepant results have triggered some controversy. The Society for Maternal-Fetal Medicine suggested that these discrepancies may reflect differences in the women sampled (eg, predominantly Caucasian and low-risk [ 6 Treatment references Labor (contractions resulting in cervical change) that begins before 37 weeks gestation is considered preterm. Risk factors include prelabor rupture of membranes, uterine abnormalities, infection... read more ]). The Society has called for additional studies but states that it is reasonable to treat women at very high risk of spontaneous preterm birth with 17-OHPC. Currently, the American College of Obstetricians and Gynecologists (ACOG) has reaffirmed its previous recommendations for the use of a progestin in future pregnancies when women are at risk of spontaneous recurrent preterm birth (7 Treatment references Labor (contractions resulting in cervical change) that begins before 37 weeks gestation is considered preterm. Risk factors include prelabor rupture of membranes, uterine abnormalities, infection... read more ). Clinicians should discuss risks and benefits of treatment with women at risk; then, decisions about treatment are made together.

Treatment references

Key Points

  • Do anovaginal cultures for group B streptococci and cultures to check for any clinically suspected infections that could have triggered preterm labor (eg, pyelonephritis, STIs).

  • Treat with antibiotics effective against group B streptococci pending culture results.

  • If the cervix dilates, consider tocolysis with magnesium sulfate, a calcium channel blocker, or, if the fetus is ≤ 32 weeks, a prostaglandin inhibitor.

  • Give a corticosteroid if the fetus is ≥ 24 weeks and < 34 weeks (in some cases < 37 weeks).

  • Consider giving corticosteroids starting at gestational age 23 weeks if there is a risk of preterm delivery within 7 days.

  • Consider magnesium sulfate if the fetus is < 32 weeks.

  • In future pregnancies, consider giving a progestin to prevent recurrence.

Drugs Mentioned In This Article

Drug Name Select Trade
Pfizerpen
Principen
Ancef, Kefzol
Cleocin, Cleocin Ovules, Cleocin Pediatric, Cleocin T, CLIN, Clindacin ETZ, Clindacin-P, Clinda-Derm , Clindagel, ClindaMax, ClindaReach, Clindesse, Clindets, Evoclin, PledgaClin, XACIATO
FIRVANQ, Vancocin, Vancocin Powder, VANCOSOL
Adbeon, Alphatrex, Beta 1 Kit, Beta Derm , Betanate , Betatrex, Beta-Val, BSP 0820, Celestone, Del-Beta , Diprolene, Diprolene AF, Diprosone, Luxiq Foam, Maxivate, ReadySharp Betamethasone, Sernivo, Valisone
AK-Dex, Baycadron, Dalalone, Dalalone D.P, Dalalone L.A, Decadron, Decadron-LA, Dexabliss, Dexacort PH Turbinaire, Dexacort Respihaler, DexPak Jr TaperPak, DexPak TaperPak, Dextenza, DEXYCU, DoubleDex, Dxevo, Hemady, HiDex, Maxidex, Ocu-Dex , Ozurdex, ReadySharp Dexamethasone, Simplist Dexamethasone, Solurex, TaperDex, ZCORT, Zema-Pak, ZoDex, ZonaCort 11 Day, ZonaCort 7 Day
Makena
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NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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