Last updated:
April 25, 2025
Table Of Contents
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
- Contractions (lower abdominal pain)
- 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
- 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
- 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