Preterm labor

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Background

  • Defined as labor before 37 weeks (uterine contraction and cervical change)
  • Increased risks to child depending on age of fetus
    • Cerebral palsy, poor lung development, cognitive delay, etc
  • Can be triggered by infections, stress, hypertension, uncontrolled DM

Clinical Features

  • Similar to term labor
  • Uterine contractions q 10 min (may be irregular)
  • New onset of vaginal mucus, blood, pink discharge, amniotic fluid
  • Low back ache, vaginal pressure

Differential Diagnosis

Vaginal Bleeding in Pregnancy (>20wks)

Evaluation

  • Do NOT perform digital exam in patients who present with vaginal bleeding when >20 weeks pregnant
  • Start with ultrasound to assess position of cervix and rule out placenta previa
  • Swabs for nitrazine, fetal fibronectin (FFN), GBS culture should also precede digital exam
    • Some lubricants can affect FFN and amniotic fluid pH strip
    • Nitrazine test (5% FP rate, 1% FN rate) - pH swab turns blue, indicating alkalotic amniotic fluid (pH 6.5 - 7.5 positive test); do not touch to mucous plug in cervix[1]
  • Proceed with digital exam if placental previa unlikely, and digital exam is urgently needed to assist patient care, such as in fetal HR decels

Management

  • IV access, ABCs
  • Fetal Heart Monitor
  • U/S to assess placental position / fetal position
  • Digital exam to assess cervical thickness, effacement, rupture of membranes
  • Type and Screen, CBC, Chem 10, Coags, U/A with culture, Utox (cocaine increases risk of abruption)

Cervical length

  • >30mm - Labor less likely
    • Observation of 6 hours might be appropriate
  • 20-30mm - Increased risk for preterm labor
    • Fetal fibernetin result can assist, if over 50ng/ml manage labor actively
  • <20mm - labor very likely
    • Manage actively

Management by Weeks

  • 24-32 weeks
    • Mag sulfate (neuroprotection against cerebral palsy)
  • <34 weeks
    • Hospitalization
    • Betamethasone 12mg IM q24hrs x2 doses
    • Tocolytics (see below for options/dosages)
    • Antibiotics for GBS prophylaxis if status unknown
    • Other antibiotics only indicated in setting of active infection

Tocolysis

  • Indications
    • Only if fetus would benefit from delay in delivery of 48 hrs
    • Gestational age 22wks - 34 wks
    • Transport to facility for definitive delivery
    • Delay in delivery for treatment of reversible condition possibly triggering labor (UTI/pyelo)
      • Betamethasone requires approximately 48 hrs for maximal benefit for lung maturity, reducing intraventricular hemorrhage, NEC, and death
      • Tocolysis rarely effective for longer than 48 hrs
      • Does not remove underlying cause for tocolysis
  • Contraindications
    • Intratuterine fetal demise / lethal anomaly
    • Maternal hemorrhage or instability
    • Intraamniotic infection
    • Severe preeclampsia or eclampsia
    • Nonreassuring fetal status
    • Contraindications to the drugs
  • Medications
    • Indomethacin 50-100mg loading dose, 25mg q4-6 hrs for 48 hrs
    • Nifedipine 20mg x1, additional 20mg dose in 90min if ctx persist, followed by 20mg q3-8 hrs PRN ctx
    • Terbutaline 0.25mg sq q20-30 min up to 4 doses PRN ctx

Disposition

  • Admission to OB floor for delivery, or transfer to facility to manage delivery
  • If cervix >30mm, contractions have stopped, consider 6 hours of obs

See Also

External Links

References

  1. Nitrazine Test. https://www.pathology.med.umich.edu/poc/onsite/pH-amniotic.html
  • UpToDate "Overview of preterm labor and birth"
  • UpToDate "Inhibition of acute preterm labor"