To examine recent trends in obstetric intervention rates among women at low-risk of poor pregnancy outcome.
Cross-sectional analytic study.
Setting and Population
A population of 336,189 women categorised as low-risk of a poor pregnancy outcome who gave birth to a live singleton in NSW from 1 January 1990 to 31 December 1997.
Main outcome measures
Obstetric intervention rates including oxytocin induction and augmentation of labour, epidural analgesia, instrumental births, caesarean section and episiotomy.
Trends over time were assessed by fitting trend-lines to numbers of births or by trends in proportions. Unconditional logistic regression was used to assess the impact of epidural analgesia on instrumental birth over time.
Rates of operative births did not rise despite increases in maternal age and use of epidural analgesia. Instrumental births declined over time from 26% to 22% among primiparas and 5% to 4% among multiparas. There was also a shift to vacuum extraction rather than forceps. Although instrumental birth was strongly associated with epidural analgesia, the strength of the association declined over the study period, for primiparas from an adjusted odds ratio of 7.2 to 5.2 and for multiparas from 13.2 to 10.3.
Increased use of epidural analgesia for labour has been a feature of the management of birth at term during the 1990s. The decline in the strength of association between epidural analgesia and instrumental birth may reflect improved epidural techniques and management of epidural labour, and recognition of the adverse maternal outcomes associated with forceps and vacuum births.