Objective: To ascertain the demographic, pregnancy and obstetric factors associated with the delivery of a liveborn very preterm infant ( < 33 weeks of gestation) and to investigate any differences in these factors between identifiable aetiological groups.
Design: Cohort analytical study.
Setting: King Edward Memorial Hospital for Women (KEMH), Western Australia.
Main variables examined: Maternal demographic and obstetric history, primary complication associated with delivery, obstetric management and mode of delivery.
Results: Six hundred and eight women who were delivered of 693 liveborn very preterm infants in Western Australia between 1.1.90 and 31.12.91, representing 1.22% of all women who were delivered of a liveborn infant in those years. Singleton pregnancy occurred in 517 (85%) and 541 (89%) were delivered in KEMH. Mean maternal age was 28 years with an excess of mothers less than 20 years of age and older than 34 years compared with the statewide perinatal data. Pre-eclampsia (n = 128, 21.1%), preterm prelabour rupture of membranes (n = 148, 24.3%), idiopathic preterm labour (n = 195, 30.4%) and antepartum haemorrhage (n = 111, 18.3%) were associated with 94.1% of deliveries. These proportions varied with plurality and period of gestation. Demographic details, use of antenatal steroids, exposure to labour and caesarean section delivery differed between mothers depending on the primary complication. Overall 322 (53.0%) received antenatal steroids and 297 (48.8%) were delivered by caesarean section. Factors associated with decreased use of steroids were gestational age of less than 27 weeks (odds ratio (OR) 0.54; 95% CI 0.36-0.83), preterm prelabour rupture of the membranes (OR 0.48; 95% CI 0.29-0.78) and idiopathic preterm labour (OR 0.56; 95% CI 0.35-0.91). Factors associated with increased use of steroids were multiple pregnancy (OR 1.70; 95% CI 1.02-2.81) and pre-eclampsia (OR 1.87; 95% CI 1.09-3.19).
Conclusions: These very preterm deliveries account for only a small proportion of all deliveries. There are differences in the mother's demographic history, obstetric management and delivery depending on the primary aetiological factor.