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Countdown to Intern Year, Week 2: Preterm Labor

We hope our Week 1 review of Abnormal Uterine Bleeding was helpful to you. This week, we continue our “Countdown to Intern Year” series with a brief review of the work up and management of Preterm Labor. Don’t forget to check out the additional resources below, including advice from our seasoned JFAC young physicians as well as links to ACOG wellness and clinical resources. 

Hope you have some time to relax during this post-graduation-pre-internship time. And remember, your JFDAC has got your back! 

Week 2 : Preterm Labor

Risk Factors, Assessment and Management

Content adapted from Relevant ACOG Practice Bulletins and AAFP Guidelines

What is Preterm Labor?

  • Between 20w 0d - 36w 6d weeks EGA
  • Criteria: “regular uterine contractions accompanied by a change in cervical dilation, effacement, or both, or initial presentation with regular contractions and cervical dilation of at least two cm”


Risk Factors for Preterm Labor

  • History of Preterm Birth
  • Cervical length < 25mm
  • Prior cervical surgery
  • Vaginal bleeding
  • UTIs/genital tract infection
  • Periodontal infections
  • Smoking
  • Substance abuse
  • Low maternal BMI
  • Short interpregnancy intervals (18-23 months or less)

The Low-Down on the Work-Up

Table 2. Initial Assessment of Women with Preterm Contractions
Questions Assessment

Are the membranes ruptured?

History of leaking fluid: observed leakage or pooling of fluid from cervical os on sterile speculum examination

Positive nitrazine test result

Arborization or ferning of fluid on microscopy

Positive amniotic protein test result (e.g., placental alpha microglobulin-1 [Amnisure])

Ultrasound assessment shows low amniotic fluid

Ultrasound guided transabdominal instillation of indigo carmine dye into the amniotic sac, if available, shows dye outside the amniotic sac

Is the patient in labor?

Observe for regular contractions accompanied by progressive dilation and cervical effacement

Is there an infection?

Evaluate for group B streptococcus carrier status, urinary tract infection, bacterial vaginosis, and sexually transmitted infections (trichomoniasis, gonorrhea, or chlamydia); treat as appropriate

What is the likelihood that the patient will deliver prematurely?

Negative fetal fibronectin test results and cervical length of at least three cm on ultrasonography have a low likelihood of delivery within 14 days

Adapted with permission from Sayres WG Jr. Preterm labor. Am Fam Physician. 2010;81(4):480, with additional information from reference 29.




1) Antenatal Corticosteroids

  • Objective: maturation of fetal lungs and other developing organ systems
  • Dosing:
    • Two 12-mg doses of betamethasone given IM 24 hours apart
    • Four 6-mg doses of dexamethasone given IM q 12 hours
    EGA, at risk for delivery < 7 days Antenatal Steroid Course?

    < 23w 0d


    Steroid administration linked to family’s decision regarding resuscitation. Must orient patient according to NICU availability and their survival rate.

    23w 0d

    Consider single course of corticosteroids

    24w 0d–34w 0d

    Single course of corticosteroids

    Consider 1x repeat course in women < 34w 0d, at risk of delivery within 7 days, whose 1st course of steroids was administered more than 14 days ago.

    34w 0d–36w 6d

    Consider single course of corticosteroids


    Applicable if the patient has NOT previously received corticosteroids.

2) Magnesium Sulfate

  • Objective: reduce severity and risk of cerebral palsy in surviving infants
  • Administer to: < 32w 0d EGA

3) Short-Term Tocolytic Therapy

  • Objective: cessation of uterine contractions to enable administration of corticosteroid therapy and/or transport
  • Administer to:
    • < 34w 0d
    • May be times when appropriate to administer before viability (s/p intra-abdominal surgery, etc.) but efficacy remains unproved
    • Maintenance therapy is ineffective and does not improve outcomes
    • Usually provided until 24 hours after last dose of corticosteroids in order to allow corticosteroids dose to be completed


Contraindications to Tocolysis

  • Intrauterine fetal demise
  • Lethal fetal anomaly
  • Nonreassuring fetal status
  • Severe preeclampsia or eclampsia
  • Maternal bleeding with hemodynamic instability
  • Chorioamnionitis
  • Preterm premature rupture of membranes*
  • Maternal contraindications to tocolysis (agent specific)

*In the absence of maternal infection, tocolytics may be considered for the purposes of maternal transport, steroid administration, or both.

Tocolytic Therapy Dosing Contraindication

Calcium Channel Blockers (nifedipine)

30-mg loading dose orally, then 10 to 20 mg every 4 to 6 hours (maximal dosage: 180 mg per day)

Hypotension and preload-dependent cardiac lesions, such as aortic insufficiency

NSAIDs (Indomethacin) - before 32 weeks EGA

50- to 100-mg loading dose orally or rectally, then 25 to 50 mg orally every 4 to 6 hours

Platelet dysfunction or bleeding disorder, hepatic dysfunction, gastrointestinal ulcerative disease, renal dysfunction, asthma (in women with hypersensitivity to aspirin)

Magnesium Sulfate

*4-6-g bolus intravenously over 20 minutes, then 2 g per hour as continuous infusion

Myasthenia gravis

Adapted from AAFP 2017 Preterm Labor: Prevention and Management
*alternative dosing regimens present



For more information on the management, prediction and prevention of preterm labor, check out the resources below. We’ll be back next week with a brief review of hypertensive disorders of pregnancy!

ACOG Resources

General Resources

If you have any feedback or requests for topics to be covered, please reach out to Samhita Nelamangala at [email protected].