Spontaneous Preterm Labour

Spontaneous preterm labour is the onset of regular contractions with progressive cervical change (dilatation of 3 cm or more or effacement of 80 percent or more) before 37 weeks, with intact or ruptured membranes, and without a medical reason to deliver. It is driven by intrauterine infection or inflammation, cervical insufficiency, uterine overdistension, bleeding or stress. It is the commonest cause of preterm birth and a leading cause of neonatal death.

• Risk factors: previous preterm birth, twin pregnancy, short cervix, genital tract infection, polyhydramnios, antepartum bleeding, smoking, anaemia, HIV, malaria, teenage pregnancy, short interval between pregnancies.
• Babies born before 34 weeks need neonatal intensive care or kangaroo mother care.
• Steroids and magnesium sulphate lower neonatal death and brain injury.

Women have regular painful contractions, backache, pelvic pressure, a bloody show or leaking fluid. Examination shows a firm contracting uterus and a cervix that is soft, effaced and dilated.

• Cervical dilatation of 3 cm or more with contractions every 5 minutes or less.
• Fever or foul discharge suggests chorioamnionitis.
• Differential diagnosis: threatened preterm labour, Braxton Hicks contractions, abruption, urinary tract infection, appendicitis, rupture of membranes without labour.
• Complications: preterm birth, respiratory distress syndrome, intraventricular haemorrhage, necrotising enterocolitis, neonatal sepsis, cerebral palsy, neonatal death, postpartum haemorrhage, endometritis.

The diagnosis is made by contractions with cervical change, and tests identify infection, rupture and fetal condition.

• Sterile speculum examination for liquor, bleeding and dilatation; one gentle digital examination once rupture and previa are excluded.
• Cardiotocography with tocography; ultrasound for presentation, estimated fetal weight, liquor and placental site.
• Full blood count, C-reactive protein, urine culture, high vaginal and rectovaginal swab, malaria test, blood pressure, urine protein, group and cross-match.
• Transvaginal cervical length or fetal fibronectin only when the cervix is less than 3 cm dilated.

The principle is to prepare the baby with steroids and magnesium sulphate, treat infection, and deliver in a unit with neonatal care.

• Supportive: transfer to a unit with neonatal intensive care if below 34 weeks; left lateral position; two cannulae; continuous fetal monitoring; delayed cord clamping for 30 to 60 seconds; warm environment and plastic wrap for babies below 32 weeks; kangaroo mother care after birth.
• Pharmacological: betamethasone 12 mg IM twice, 24 hours apart, between 24 weeks and 34 weeks and 6 days; magnesium sulphate 4 g IV over 20 minutes then 1 g per hour until delivery for 24 hours at most, before 32 weeks (stop for absent patellar reflexes, respiratory rate below 12 per minute or urine below 30 mL per hour, with calcium gluconate 1 g IV over 10 minutes for toxicity); nifedipine 20 mg oral once then 10 to 20 mg oral every 6 to 8 hours for up to 48 hours (maximum 120 mg daily) when the cervix is less than 4 cm dilated and there is no infection or bleeding; benzylpenicillin 5 million units IV then 2.5 million units 4-hourly until delivery for group B streptococcus carriage or unknown status; ampicillin 2 g IV 6-hourly plus gentamicin 5 mg/kg IV once daily for chorioamnionitis; oxytocin 10 IU IM at birth.
• Procedures: vaginal birth for a cephalic baby with a small or no episiotomy; caesarean section for breech presentation, transverse lie, fetal compromise or abruption; remove any cerclage at once.
• Special groups: breech presentation before 32 weeks is usually delivered by caesarean section; women with a scar avoid misoprostol and oxytocin without senior review; diabetes needs insulin increased by 25 to 40 percent for 72 hours after steroids; RhD negative women with bleeding give anti-D immunoglobulin 500 IU IM within 72 hours.
• Red flags: fever above 38 degrees Celsius, bleeding, rupture of membranes, fetal heart rate above 160 or below 110 beats per minute, cord prolapse, maternal breathlessness on tocolysis.
• Follow-up: neonatal care and feeding support; maternal temperature 4-hourly for 24 hours after birth; review at 6 weeks; preterm birth prevention plan for the next pregnancy.