Disappearance of meconium pigment in placental specimens on exposure to light

Meconium discharge has been associated with fetal distress and poor neonatal outcome; thus, its presence is of clinical importance.

Loss of meconium pigment in histologic sections from light exposure has been described. We sought to confirm this finding and to measure this loss quantitatively.

Sections of umbilical cord, fetal membranes, and fetal surface from 11 grossly meconium-stained placentas were processed swiftly to minimize light exposure. Two serial sections from each block were cut and stained; one set was reviewed immediately, and the other was exposed to 8 hours of direct fluorescent lighting. Each site and exposure was scored for pigment intensity (0, no staining; 1, weak expression; and 2, moderate/strong expression) and number of meconium-laden macrophages per 10 high-power fields (HPF). Results were compared on the same specimen using the chi(2) and the paired-samples t test.

The maximum meconium macrophage count was 13.2/10 HPF in the unexposed sections versus 6.1/10 HPF in the exposed sections (P <.001). Unexposed sections varied from 1+ to 2+ intensity, while exposed sections were all 1+ or negative (P <.001).

Exposure to fluorescent laboratory lights for 8 hours resulted in a significant loss in the intensity and number of identifiable meconium macrophages in histologic sections. These findings have important implications in the handling of placental specimens, and we recommend that care be taken to minimize exposure to laboratory lights during processing.