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

Objective To examine trends in the distribution of births at and beyond ter m in New South Wales and in particular, to determine whether any changes ar e associated with changes in the obstetric practices of induction and elect ive caesarean section. Design Cross-sectional analytic study. Setting New South Wales, Australia. Population All 540,162 women delivering a singleton cephalic-presenting inf ant of gestational age greater than or equal to 37 weeks from 1 January 199 0 to 31 December 1996. Methods Data were obtained from the New South Wales midwives data collectio n, 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 ra tes. Results From 1990 to 1996 there was a significant decrease in births report ed as 40 weeks of gestation, from 35,670 (46.3%) to 30,651 (40.3%). These d eclines were offset by significant increases in births at 38 and 39 weeks. Births greater than or equal to 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 sec tions and induction at 38 and 39 weeks, and increasing maternal age. Conclusions Clinicians appear to be implementing the recommendations of ran domised controlled trials to offer induction after 41 weeks of gestation. H owever the trend of performing elective caesarean sections at earlier gesta tional ages may be unnecessarily putting some infants at increased risk of respiratory morbidity.