Preterm Labour

Introduction

Preterm labour is a critical topic for the MCCQE1 exam and an essential component of Canadian obstetric care. This comprehensive guide will help you prepare for questions related to preterm labour on the MCCQE1, with a focus on Canadian guidelines and practices.

Definition and Epidemiology

Preterm labour is defined as regular contractions of the uterus resulting in changes in the cervix that start before 37 weeks of pregnancy.

Canadian Epidemiology

• Preterm birth rate in Canada: Approximately 8% of live births
• Leading cause of infant morbidity and mortality in Canada
• Higher rates among Indigenous populations and in northern territories

Risk Factors

Understanding risk factors is crucial for MCCQE1 preparation, especially in the Canadian context.

Clinical Presentation and Diagnosis

For the MCCQE1, focus on recognizing the signs and symptoms of preterm labour and understanding the diagnostic criteria used in Canadian practice.

Symptoms

• Regular uterine contractions (≥4 in 20 minutes or ≥8 in 60 minutes)
• Abdominal cramping or pain
• Increased pelvic pressure
• Vaginal discharge changes
• Low back pain

Diagnosis

Management

Canadian guidelines emphasize a patient-centered approach to managing preterm labour. The MCCQE1 may test your knowledge on the following aspects:

Acute Management

1. Tocolysis: To delay delivery for 48 hours to allow for corticosteroid administration

   • First-line agents in Canada: Nifedipine or Indomethacin
   • Second-line: Atosiban (oxytocin receptor antagonist)

2. Antenatal Corticosteroids: To promote fetal lung maturity

   • Betamethasone: 12 mg IM q24h x 2 doses
   • Dexamethasone: 6 mg IM q12h x 4 doses

3. Magnesium Sulfate: For neuroprotection if <32 weeks gestation

   • Loading dose: 4 g IV over 30 minutes
   • Maintenance: 1 g/hour for 24 hours or until delivery

4. Group B Streptococcus Prophylaxis: If indicated based on Canadian guidelines

Ongoing Management

• Bed rest (controversial, not routinely recommended)
• Hydration
• Fetal and maternal monitoring
• Treatment of underlying causes (e.g., antibiotics for infections)

Prevention

For MCCQE1 preparation, focus on evidence-based preventive strategies used in Canadian practice:

1. Progesterone supplementation for high-risk women (e.g., previous preterm birth, short cervix)
2. Cervical cerclage for women with a history of preterm birth and short cervix
3. Smoking cessation programs
4. Adequate prenatal care and education
5. Treatment of asymptomatic bacteriuria and other infections

Complications

Understanding potential complications is crucial for the MCCQE1 exam:

Maternal Complications

• Infection
• Cesarean delivery
• Psychological distress

Fetal/Neonatal Complications

• Respiratory distress syndrome
• Intraventricular hemorrhage
• Necrotizing enterocolitis
• Retinopathy of prematurity
• Long-term neurodevelopmental issues

Key Points to Remember for MCCQE1

• 🇨🇦 Canadian preterm birth rate is approximately 8%
• Definition: Regular contractions with cervical changes before 37 weeks gestation
• Risk factors: Previous preterm birth, short cervix, multiple gestation
• Diagnosis: Clinical presentation, cervical assessment, fFN test, transvaginal ultrasound
• Management: Tocolysis, antenatal corticosteroids, magnesium sulfate for neuroprotection
• Prevention: Progesterone, cervical cerclage, smoking cessation, adequate prenatal care
• Complications: Focus on both short-term and long-term outcomes for mother and baby

Canadian Guidelines

The Society of Obstetricians and Gynaecologists of Canada (SOGC) provides specific guidelines for managing preterm labour:

1. Antenatal corticosteroids are recommended for all women between 24+0 and 34+6 weeks of gestation at risk of preterm birth within 7 days
2. A single rescue course of antenatal corticosteroids may be considered if the first course was administered at least 14 days previously
3. Tocolysis should be considered to allow for completion of antenatal corticosteroids and in-utero transfer to a tertiary care center
4. Magnesium sulfate for neuroprotection should be considered for all women presenting with imminent preterm birth before 32 weeks of gestation

Sample Question

# Sample Question

A 28-year-old woman, G2P1, presents at 29 weeks gestation with regular uterine contractions every 5 minutes for the past hour. On examination, her cervix is 2 cm dilated and 50% effaced. Which of the following management steps should be initiated first?

- [ ] A. Administer nifedipine for tocolysis
- [ ] B. Start magnesium sulfate for neuroprotection
- [ ] C. Perform a fetal fibronectin test
- [ ] D. Administer betamethasone for fetal lung maturity
- [ ] E. Transfer the patient to a tertiary care center

Explanation

The correct answer is:

• D. Administer betamethasone for fetal lung maturity

Explanation: In this scenario of preterm labour at 29 weeks gestation, the most urgent intervention is the administration of antenatal corticosteroids for fetal lung maturity. According to Canadian guidelines, all women between 24+0 and 34+6 weeks of gestation at risk of preterm birth within 7 days should receive antenatal corticosteroids. This intervention has been shown to significantly reduce neonatal morbidity and mortality.

While the other options are also important in managing preterm labour, they should follow the initiation of corticosteroids:

• Tocolysis (A) can be considered to allow time for corticosteroids to take effect
• Magnesium sulfate (B) is recommended for neuroprotection but is secondary to corticosteroids
• Fetal fibronectin test (C) is not necessary as the patient already has clear signs of preterm labour
• Transfer to a tertiary care center (E) may be necessary but should not delay the administration of corticosteroids

Remember, in Canadian practice, the priority is to improve fetal outcomes in preterm labour, with corticosteroid administration being a key intervention.

References

1. Society of Obstetricians and Gynaecologists of Canada (SOGC). (2019). Management of Preterm Labour. Journal of Obstetrics and Gynaecology Canada, 41(8), 1190-1210.

2. Canadian Perinatal Health Report. (2020). Public Health Agency of Canada.

3. Crane, J., & Hutchens, D. (2018). Transvaginal sonographic measurement of cervical length to predict preterm birth in asymptomatic women at increased risk: a systematic review. Ultrasound in Obstetrics & Gynecology, 31(5), 579-587.

4. Vogel, J. P., Oladapo, O. T., Manu, A., Gülmezoglu, A. M., & Bahl, R. (2015). New WHO recommendations to improve the outcomes of preterm birth. The Lancet Global Health, 3(10), e589-e590.

5. Canadian Neonatal Network. (2021). Annual Report 2020. Retrieved from https://www.canadianneonatalnetwork.org/portal (opens in a new tab)