The incidence of meconium-stained amniotic fluid from 1980 through 1986, by year and gestational age.

The annual incidence of meconium-stained amniotic fluid was analyzed for changes in a total obstetric sample of 45,115 singleton, vertex, liveborn infants over a 7-year study period. The incidence of meconium-stained amniotic fluid for the total obstetric population was calculated for each year of the study period. The sample was then stratified by estimated gestational age, and the incidence of meconium-stained amniotic fluid was calculated for each gestational age group. The incidence of meconium-stained amniotic fluid increased 40.9% over the study period, from 18.8% in 1980 to 26.5% in 1986 (P less than .001). This increase was found to be in a consistent linear trend (P less than .05). The incidence of meconium-stained amniotic fluid was also found to increase significantly in a linear trend as gestational age of the fetus increased. These findings lend support to both the maturational theory and the stress theory of meconium passage in utero.