Trends in the distribution of gestational age and contribution of planned births in New South Wales, Australia

PLoS One. 2013;8(2):e56238. doi: 10.1371/journal.pone.0056238. Epub 2013 Feb 20.


Background: There is concern that the rate of planned births (by pre-labour caesarean section or induction of labour) is increasing and that the gestation at which they are being conducted is decreasing. The aim of this study was to describe trends in the distribution of gestational age, and assess the contribution of planned birth to any such changes.

Methods: We utilised the New South Wales (NSW) Perinatal Data Collection to undertake a population-based study of all births in NSW, Australia 1994-2009. Trends in gestational age were determined by year, labour onset and plurality of birth.

Results: From 1994-2009, there was a gradual and steady left-shift in overall distribution of gestational age at birth, with a decline in the modal gestational age from 40 to 39 weeks. For singletons, there was a steady but significant reduction in the proportion of spontaneous births. Labour inductions increased in the proportion performed, with a gradual and changing shift in the distribution from a majority at 40 weeks to an increase at both 37-39 weeks and 41 weeks gestation. The proportion of pre-labour caesareans also increased steadily at each gestational age and doubled since 1994, with most performed at 39 weeks in 2009 compared with 38 weeks up to 2001.

Conclusions: Findings suggest a changing pattern towards births at earlier gestations, fewer births commencing spontaneously and increasing planned births. Factors associated with changing clinical practice and long-term implications on the health and well-being of mothers and babies should be assessed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Age Distribution
  • Australia
  • Cesarean Section / statistics & numerical data*
  • Cesarean Section / trends*
  • Female
  • Gestational Age*
  • Humans
  • Labor, Induced / statistics & numerical data*
  • Labor, Induced / trends*
  • Mothers
  • Pregnancy
  • Pregnancy Outcome

Grant support

MS and this work were funded by an Australian National Health and Medical Research Council (NHMRC) Centre for Research Excellence Grant (#1001066). CLR is funded by a NHMRC Senior Research Fellowship (#457078) and NN by a NHMRC Career Development Fellowship (#632955). The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. (URL: