Objective assessment of meconium content of amniotic fluid.

The amount of meconium in amniotic fluid is subjectively estimated by visual inspection and classified as thin (light), moderate, or thick (heavy). This estimate may be important for assessing the neonatal risk of perinatal asphyxia and meconium aspiration syndrome. This study reports on the "meconium-crit," a simple, rapid, inexpensive, and reproducible method of quantifying meconium concentration in amniotic fluid. The purpose of the study was to determine the relationship between the meconium-crit and meconium concentration. Specimens were prepared by placing 3.0 g of fresh neonatal meconium into clear amniotic fluid and vortexing for 15 minutes to obtain a stock solution of 15.0 g meconium/100 mL amniotic fluid. Stock solutions were then diluted with clear amniotic fluid to obtain concentrations of 10.0, 7.5, 5.0, 3.0, and 1.5 g/100 mL. One-tenth milliliter of the amniotic fluid/meconium mixture was drawn into a standard hematocrit tube and centrifuged. The meconium-crit was then measured directly as with a hematocrit. Regression analysis indicated that meconium-crit values were linearly related to meconium concentration (r = 0.901-0.995). This method provides a reproducible means of quantifying meconium in amniotic fluid.