Preterm labour and preterm prelabour rupture of membranes

What it is

Preterm labour is labour after 20 and before 37 weeks of gestation: late preterm at 34 to 36 weeks and 6 days, moderate at 32 to 33 weeks, very preterm before 32 weeks, extreme before 28 weeks. Ruptured membranes carry three names: pPROM preterm, tPROM term, PPROM prolonged premature rupture of membrane. Lung maturity is achieved at 34 weeks and completed at term, surfactant being secreted by 20 weeks and seen in the amniotic fluid at 28 weeks.

Causes and risk

The causes are infection, that is chorioamnionitis and bacterial vaginosis; obstetric ones, multiple pregnancy, polyhydramnios, PPROM, placental abruption, cervical insufficiency and uterine anomalies; a past preterm birth; an iatrogenic termination for pre-eclampsia or IUGR; and the unexplained. Demographic factors are extremes of maternal age and weight, a short interpregnancy period and smoking. Rupture of membranes adds a previous PROM, trauma, and a nutritional deficiency of Vit C or zinc.

How it presents

Established preterm labour is set by three criteria together:

1. 4 or more contractions in 20 min
2. Cervical effacement of 80%
3. Dilatation of 2 cm or more