Trends and characteristics of women undergoing induction of labour in a tertiary hospital setting: A cross-sectional study.

Background: In many well-resourced countries, rising rates of intervention are being observed during pregnancy, labour and childbirth with induction of labour (IOL) fast becoming one of the most common. In Australia, the rate of induction of labour has increased by over 30% since 2007, and today one in three women have their labours induced. We do not however have a good understanding of the contribution of specific obstetric populations to this trend.

Methods: We examine the contribution of specific obstetric populations to induction of labour over a six-year period at one tertiary maternity service, using the Nippita classification system. Average Annual Percentage Changes (AAPC) were calculated along with 95% confidence intervals and P values set at 0.05.

Results: The overall rate of induction of labour increased from 21.3% in 2012 to 30.9% in 2017, representing an Average Annual Percent Change of 8.1, P<0.0001 (95% CI 7-9.6). The greatest AAPC was seen in group 5 (parous, no previous caesarean section, 39-40 weeks, single cephalic), followed by group 2 (nulliparous, 39-40 weeks, single cephalic) and 1 (nulliparous, 37-38 weeks, single cephalic).

Conclusions: The use of the Nippita classification system allowed for standardised comparison across timepoints, facilitating identification of the subpopulations driving changes in rates of induction of labour. Rates of induction of labour saw a year on year increase which in this maternity service, it is not being driven by post-dates pregnancies. Further work is required to understand the role of other potential contributors such as diabetes.