Background Information

Definition

Gestational age definitions:

• Preterm: <37 weeks of gestation
  • Preterm birth may or may not be preceded by preterm prelabour rupture of membranes (PPROM)
  • Preterm labour: regular uterine contractions with progressive cervical dilatation (from 4cm) at <37 weeks
• At term: 37 – 41⁺⁶ weeks of gestation
• Post-term: ≥42 weeks of gestation

P-PROM, preterm labour, and PROM may have similar names but are very different:

Preterm Labour Guidelines

Prevention in High-Risk Women

Individuals at risk of preterm labour:

• History of spontaneous preterm birth or loss
• TVUS shows cervical length ≤25 mm (carried out at 16-24 weeks gestation)
• P-PROM in previous pregnancy
• History of cervical trauma

Prophylactic options:

• Vaginal progesterone – start between 16-24 weeks, until at least 34 weeks
• Cervical cerclage 

Investigation and Diagnosis

First, perform clinical assessment and speculum examination

• Regular contractions reported by patient AND progressive cervical dilation from 4cm, at <37 weeks, suggests preterm labour (as per definition)

If clinical assessment suggests preterm labour:

• <30 weeks → clinical diagnosis with no further

• ≥30 weeks → additional tests
  • 1st line: TVUS to measure cervical length 
    • Cervical length ≤15 mm → diagnose preterm labour
    • Cervical length >15 mm→ preterm labour unlikely

• • 2nd line: swab for fetal fibronectin testing (swab before digital vaginal examination)
    • Indication
      • consider in suspected preterm labour ≥30 wks, when TVUS cannot be conducted
    • Interpretation
      • >50 ng/mL (positive) → diagnose preterm labour
      • ≤ 50 ng/mL (Negative) → preterm labour unlikely
    • False +ve result may occur in the following instances:
      • Digital vaginal examination (swab taken before any digital vaginal examination)
      • Recent sexual intercourse (within 24–48 hours)
      • Recent vaginal bleeding

Management

There are 3 main domains in the management of preterm labour with intact membranes:

• Tocolysis
• Maternal corticosteroids
• Maternal magnesium sulfate

Tocolysis

Purpose:

• Suppress uterine contractions
• Delays preterm delivery, usually up to 48 hours so that other interventions (e.g., steroids and magnesium sulfate) or transfer to a higher-level facility can be arranged

Choice of agent:

• 1st line: nifedipine PO
• 2nd line: oxytocin receptor antagonist (e.g., atosiban)

Indications:

• In short, indicated in <34 weeks of gestation PLUS intact membranes with suspected/confirmed preterm labour
• Exact recommendation
  • Offer if 26 – 33+6 weeks
  • Consider if 24 – 25+6 weeks

Maternal Corticosteroids

Purpose:

• Mainly stimulate surfactant production in the fetal lung → reduce risk of respiratory distress syndrome
• Also reduces risk of intraventricular haemorrhage and necrotising enterocolitis

Choice of agent:

• IM betamethasone 
• Do not give more than 2 courses of maternal corticosteroids for preterm birth

Indications:

• In short, indicated in <36 weeks of gestation
• Exact recommendation
  • Offer if 24 – 33+6 weeks
  • Consider if 34 – 35+6 weeks

Maternal Magnesium Sulfate

Purpose:

• Fetal neuroprotection – reduces risk of cerebral palsy
  • Magnesium stabilises neuronal membranes, reducing risk of excitotoxic injury

Choice of agent:

• IV magnesium sulfate (4g bolus over 15 min, followed by 1g / hour until birth or for 24 hours)

Indications:

• In short, indicated if <34 weeks
• Exact recommendation
  • Offer if 24 – 29+6 weeks
  • Consider if 30 – 33+6 weeks

Emergency Cervical Cerclage

Only consider if all the following are present:

• <28 weeks of gestation
• Dilated cervix
• Exposed and unruptured fetal membrane

P-PROM Guidelines

Investigation and Diagnosis

If P-PROM is suspected:

• 1st line: speculum examination – look for pooling of amniotic fluid
  • If no amniotic fluid pooling on speculum → consider vaginal fluid testing for IGFBP-1  / PAMG-1  (+ve test/detection indicates P-PROM)
  • If IGFBP-1 / PAMG-1 is not detected (-ve test)→ P-PROM unlikely

Management

There are 3 main domains in the management of PPROM:

• Prophylactic antibiotic – ALL patients
• Maternal corticosteroid – selected patients
• Maternal magnesium sulfate – selected patients

Prophylactic Antibiotic

Prophylaxis for intrauterine infection is indicated for ALL patients with PPROM:

• 1st line: erythromycin 250mg PO QDS until labour / maximum of 10 days (whichever is sooner)
• 2nd line: penicillin PO

Maternal Corticosteroids

Purpose:

• Mainly stimulate surfactant production in the fetal lung → reduce risk of respiratory distress syndrome
• Also reduces risk of intraventricular haemorrhage and necrotising enterocolitis

Choice of agent:

• IM betamethasone / dexamethasone
• Do not give more than 2 courses of maternal corticosteroids for preterm birth

Indications:

• In short, indicated in <36 weeks of gestation
• Exact recommendation
  • Offer if 24 – 33+6 weeks
  • Consider if 34 – 35+6 weeks

Maternal Magnesium Sulfate

Purpose:

• Fetal neuroprotection – reduces risk of cerebral palsy
  • Magnesium stabilises neuronal membranes, reducing risk of excitotoxic injury

Choice of agent:

• IV magnesium sulfate (4g bolus over 15 min, followed by 1g / hour until birth or for 24 hours)

Indications:

• In short, indicated if <34 weeks
• Exact recommendation
  • Offer if 24 – 29+6 weeks
  • Consider if 30 – 33+6 weeks

Timing of Delivery

If PPROM <34 weeks:

• Expectant management until 37 weeks (unless there are additional indications for expedited delivery)

If PPROM 34-37 weeks:

• Offer the option of:
  • Expectant management until 37 weeks OR
  • Induction of labour 

• If +ve GBS during current pregnancy → immediate induction of labour or caesarean birth + maternal IAP with IV benzylpenicillin

Identifying Infection in P-PROM

Use a combination of clinical assessment and:

• CRP
• White blood cell count
• Cardiotocography

Delivery of Preterm Babies

Mode of Birth

• Discuss general benefits and risks of caesarean birth and vaginal birth
  • NICE particularly mentions the increased risk of classical incision while performing a caesarean birth of preterm birth

• Explain that risks are specific to gestational age, not mode of birth

Intrapartum Antibiotic Prophylaxis (IAP)

RCOG recommends IAP with benzylpenicillin for all established preterm labour to prevent GBS disease

• This is irrespective of maternal GBS carrier status

Cord Clamping

Prelabour Rupture of Membrane (PROM) at Term

Assessment

Advise women with suspected PROM after 37 weeks (i.e. at term) to contact their midwife / maternity unit to have an initial triage assessment over the phone.

Risk Factors to Exclude

The following factors should be excluded in the initial phone triage:

• Maternal factors
  • Abnormal liquor
    • Meconium-stained
    • Blood-stained
    • Any change in smell and colour
  • Vaginal bleeding 
  • GBS carriage / infection in this or previous pregnancy
  • Continuous abdominal pain
  • Reduced fetal movements
• Fetal factors
  • Abnormal lie or presentation (e.g. transverse lie or breech)
  • Fetal growth restriction
  • Low-lying placenta

Subsequent Action

If ANY of the above risk factors are present or if any uncertainty → advise the woman to immediately maternity unit 

If none of the above risk factors are present:

• See the women within 12 hours, or
• ASAP if she has any concerns or wishes to be induced immediately

Management

Offer the women EITHER of the following:

• Expectant management for up to 24 hours, then offer induction (if labour not started naturally), or
• Induce labour immediately

For more information on labour induction, see this article.

References