The effect of immersion formaldehyde fixation on placental weight

Abstract

The normal reference ranges for placental weight are based on fresh placental status; however, in routine practice, placentas are frequently received in formaldehyde solution prior to the examination. The aim of this study was to assess the effect of formalin fixation on placental weight and the underlying factors affecting this process. We prospectively studied 71 placentas and measured their fresh weight and volume as well as their weight in five consecutive days following fixation in 10% formaldehyde solution. The volume of formalin added primarily and also findings of subsequent macroscopic and histological examination were recorded. The results showed a significant 8.47% (SD 6.33%, p — 0.000) increase in placental weight after formalin fixation for 24 h. This weight change was reversely correlated with fresh placental weight (r — -0.59, p — 0.000) and also had a poor positive correlation with formalin to placenta volume ratio (r = 0.31, p = 0.04). Mean placental weight remained approximately constant in the following days of follow-up. Association between the placental pathologies and changes in weight was also assessed. Our study showed a wide range of changes in placental weight following formalin fixation which is affected by different factors. Knowing them provides a more accurate estimation of the fresh placental weight.