- To evaluate the effect of meconium-stained amniotic fluid (AF) on perinatal outcome. A prospective observational study was performed, comparing perinatal outcome of parturients with thick and thin meconium-stained AF to those with clear AF. The rate of meconium-stained AF was 18.1% (106/586). Of those, 78 (13.3%) patients had thin and 28 (4.8%) had thick meconium-stained AF. The rate of oligohydramnios was significantly higher among pregnancies complicated with thick meconium-stained AF (OR 7.2, 95% Cl 2.1-24.1; p = 0.002). A significant linear association, using the Mantel-Haenszel test for linearity, was found between the thickness of the meconium and abnormal fetal heart rate patterns during the first and second stages of labor, low Apgar scores at 1 min and the risk for Cesarean section. A statistically significantly higher risk for neonatal intensive care unit admission was observed among patients with thick meconium as compared to those with clear AF (OR 11.4, 95% CI 2.0-59.3; p = 0.006), even after adjustment for oligohydramnios and abnormal fetal heart rate patterns. Thick, and not thin, meconium-stained AF, was associated with an increased risk for perinatal complications during labor and delivery. Therefore, thick meconium-stained AF should be considered a marker for possible fetal compromise, and lead to careful evaluation of fetal well-being.