Trends in births at and beyond term: evidence of a change?

OBJECTIVE: To examine trends in the distribution of births at and beyond term in New South Wales and in particular, to determine whether any changes are associated with changes in the obstetric practices of induction and elective caesarean section.

DESIGN: Cross-sectional analytic study.

SETTING: New South Wales, Australia.

POPULATION: All 540,162 women delivering a singleton cephalic-presenting infant of gestational age > or = 37 weeks from 1 January 1990 to 31 December 1996.

METHODS: Data were obtained from the New South Wales midwives data collection, a population-based surveillance system covering all births in New South Wales. The data were analysed to examine changes over time and associations between gestational age, maternal factors and onset of labour.

MAIN OUTCOME MEASURES: Induction of labour and elective caesarean section rates.

RESULTS: From 1990 to 1996 there was a significant decrease in births reported as 40 weeks of gestation, from 35,670 (46.3%) to 30,651 (40.3%). These declines were offset by significant increases in births at 38 and 39 weeks. Births > or = 42 weeks declined from 3321 (4.6%) to 2132 (2.8%). The decline in prolonged pregnancies was associated with increasing induction rates at 41 weeks. The re-distribution of some births from 40 to 38-39 weeks was associated with increasing rates of elective caesarean sections and induction at 38 and 39 weeks, and increasing maternal age.

CONCLUSIONS: Clinicians appear to be implementing the recommendations of randomised controlled trials to offer induction after 41 weeks of gestation. However the trend of performing elective caesarean sections at earlier gestational ages may be unnecessarily putting some infants at increased risk of respiratory morbidity.