Causes of a spontaneously premature labour

Among the natural causes of premature births are:

• 50% are of unknown aetiology
• multiple pregnancy; typically for twins, delivery is between 36 and 38 weeks, for triplets 32 weeks
• polyhydramnios
• cervical incompetence and uterine anomalies
• premature rupture of membranes; 30 to 40% labour within 24 hours of the rupture
• intrauterine infection
• maternal malnutrition
• maternal infection

Risk factors include second trimester abortions and stillbirths. There is no increase associated with previous first trimester terminations of pregnancy providing there has been atraumatic cervical dilatation. Almost any severe maternal illness may be associated with preterm delivery.