Preterm labor

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)

• Emergent delivery
• Placental abruption
• Placenta previa
• Vasa previa
• Uterine rupture
• Preterm labor
• Vaginal trauma
• Placenta accreta
• Intrauterine fetal demise

Evaluation

• Type and Screen, CBC, Chem 10, Coags, U/A with culture, Utox (cocaine increases risk of abruption)
• Do NOT perform digital exam in patients who present with vaginal bleeding when >20 weeks pregnant due to potential for placenta previa
• 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
• 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 x2, ABCs
• Fetal heart monitor
• Immediate obstetrical consult

Cervical length

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

Management by Weeks

• 24-32 weeks
  • Magnesium 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

• Intrauterine 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. (avoid in gestation >32 weeks for concern of premature narrowing or closure of the ductus arteriosus)
• 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

• Vaginal Bleeding (Main)
• Pregnancy (main)

References

• UpToDate "Overview of preterm labor and birth"
• UpToDate "Inhibition of acute preterm labor"