Trends in obstetric practices and meconium aspiration syndrome: a population-based study

Abstract

Objective: To determine trends in the incidence of meconium aspiration syndrome (MAS), and maternal factors and obstetric practices associated with any decline.

Design: Population-based cohort study.

Setting: New South Wales (NSW), Australia.

Population: All 877 037 liveborn, singleton, term infants (≥ 37 weeks of gestation) in the period 1997-2007.

Methods: Data were obtained from birth records linked to the neonatal hospital discharge records. The birth data provided information on maternal and obstetric factors, whereas the outcome of interest, MAS, was obtained from hospital data on the neonates. Multivariable logistic regression was used to estimate the risk of MAS while simultaneously adjusting for the explanatory variables.

Main outcome measures: The incidence of MAS per 1000 births, and odds ratios and 95% confidence intervals for maternal and obstetric factors for the development of MAS.

Results: The incidence of MAS declined significantly by 11.3% per annum (95% CI 10.1-12.6; P < 0.001) from 4.1 per 1000 births in 1997 to 1.3 per 1000 births in 2007. This was associated with a statistically significant decline in risk factors: maternal smoking (from 20 to 12%), gestational age (from 57 to 47% ≥ 40 weeks of gestation), delivery at small hospitals (from 15 to 9%) and infants with birthweight below the third percentile (from 3.3 to 2.4%). There were simultaneous statistically significant increases in practices that reduce the risk of MAS: labour inductions (from 22 to 27%) and birth by caesarean section, both elective, prior to 40 weeks of gestation (from 7.3 to 13.8%), and emergency (from 3.0 to 5.3% prior to 40 weeks of gestation, and from 5.1 to 6.7% at 40 weeks of gestation or later).

Conclusions: The rate of MAS is declining, and this decline is associated with a reduction in maternal and pregnancy risk factors, and an increase in protective obstetric practices.