Preterm Labour

Preterm labor and Preterm Birth

Preterm labor is defined as the onset of contractions and cervical changes between 24-37 weeks of pregnancy or weight less than 2500g in an unknown duration of pregnancy.

Definition of terms

Term	Definition
Preterm	< 37 weeks
Early term	37 – 37 6/7 weeks
Full term	38 – 40 6/7 weeks
Late term	41 – 41 6/7 weeks
Post term	> 47 weeks

Risk factors for preterm birth

Classification	Risk factors
Maternal risk factors	Previous preterm birth (especially following PPROM), low maternal BMI or overweight, cervical insufficiency, short cervical length (< 20 mm), uterine abnormalities, maternal stress (external or internal), teenage pregnancy, smoking, cocaine use, low socioeconomic status, pre-eclampsia, infections, cervical dysplasia and its treatment, use of ART, short pregnancy interval (< 6 months)
Obstetric risk factors	Chorioamnionitis (subclinical), PPROM, over-distension (multiple gestation, polyhydramnios), abruption (blood irritates myometrium and weakens membranes)
Fetal risk factors	Fetal anomalies, positive fibronectin (strong NPV), intrauterine death, multiple gestation, polyhydramnios, male fetus

• Signs and symptoms of preterm labor
  • Contractions (lower abdominal pain)
    • Abdominal tightening
    • Lower back pain
    • Pelvic pain
  • Cervical effacement and/or dilatation
  • Distinguish from cervical insufficiency where the cervix dilates without uterine contractions
• Investigations
  • Fetal fibronectin (fFN): found in cervicovaginal fluid, amniotic fluid, placental tissue and interface between chorion and decidua. Presence between 22 and 36 weeks is a predictor of preterm labour. Has a high negative predictive value
    • Positive: admit for tocolysis and steroids for fetal lung maturation
    • Negative: can be discharge
• Treatment of preterm labour
  • Tocolysis using nifedipine or atosiban: Prolong latency period to allow for corticosteroid to work and intrauterine transfer for referral to facility with NICU
  • Corticosteroids: for fetal lung maturity and to prevent intraventricular hemorrhage
  • Magnesium sulphate for neuroprotection (”..reduce the risk of cerebral palsy in surviving infants” – ACOG)
• Specific measures to reduce the incidence of pre-term labour
  • Mid-stream urine specimen durin ANC visits
  • Use of condoms in the second half of pregnancy
  • Cervical cerclage at 14 – 16 weeks for incompetence
• How can Intraventricular hemorrhage be prevented in PROM/PPROM?
  • Administration of Corticosteroids and Magnesium sulphate
  • Caesarean Delivery

Tocolytics

Tocolytic	Description	Nota bene
Beta agonists (ritordine, salbutamol and terbutalin)	Delayes delivery by activating cAMP. But does not improve neonatal outcome	Greates side effect profile. Can cause pulmonary oedema, especially when given in large amounts to women with multiple gestation and cardiac disease
Magnesium sulphate	Delayes delivery by modulating calcium uptake and distribution in smooth muscles. Provides neuroprotection
COX inhibitors (indomethacin)	Effectively delays delivery by inhibiting the synthesis of prostaglandins.	Should not be used beyon 32 weeks due to premature closure of ductus arteriosus (persistent pulmonary hypertension), increased risk of necrotizing enterocolitis, neonatal renal dysfunction and oligohydramnios
Calcium channel blocker (nifedipine)	Delayes delivery by blocking L-type calcium channels	Intermediate side effect profile
Oxytocin receptor antagonist (atosiban)	Delays delivery by inhibiting oxytocin receptors	Lowest side effect profile and is much better tolerated

• Contraindications to tocolysis
  • Chorioamnionitis
  • Hemorrhage
  • Abruption of the placenta
  • Mature fetus
  • Pre-eclampsia/Eclampsia
  • Placental insufficiency (umbilical artery resistive index > 95%)
  • Severe IUGR
  • Cervical dilatation > 8 cm
  • Fetal death
  • Fetal compromise
• Early neonatal complications of preterm birth
  • Respiratory distress syndrome
  • Necrotizing enterocoloitis
  • Intraventricular hemorrhage (IVH)
  • Hypothermia
  • Hypoglycemia
  • Neonatal jaundice
  • Apnoea
• Long-term complications of preterm birth (worse for those born < 32 weeks)
  • Chronic lung disease
  • Grade 3 and 4 IVH is associated with cerebral palsy
  • Vision and hearing impairment
  • Neurosensory impairment
  • Reduced cognition and motor performance
  • Academic difficulties
  • ADHD