ABSTRACT
Placental weight, as a clinicopathologic determinant of intrauterine placental functional adequacy, is not a fully reliable measurement since it is affected by several factors. Placental blood volume in the fetal villous tree and the maternal space varies among normal placentas delivered at similar gestational periods. Alterations also occur with fixation or storage of fresh specimens. For example, placental weight increases, on average, about 10% with fixation. Storage of fresh specimens, of 2-3 h, results in loss of weight due to drainage of most blood within the maternal space. Edematous placentas can lose significant amounts of fluid when stored for a day4. At this time, assessment of whether placental growth and function have been adequate, in a given pregnancy, is best made by calculating the fetal: placental weight ratio (Table 9)223. (For example, an increased fetal: placental weight ratio of 1.5 or more above the value expected for that period of gestation is highly suggestive of intrauterine growth restriction.) However, such calculation is often precluded by the fact that the corresponding fetal or newborn weight is rarely provided in the clinical history accompanying the placental specimen. Nevertheless, obtaining the weight of the trimmed, fresh (refrigerated) specimen and correlating it with the expected range for the period of gestation (Table 10)224 can be very informative. The need for sophisticated analysis and the shortcomings of isolated
Weight of placenta (g)Gestational week Mean 1 SD
Ratio of fetal to placental weight
weight measurement can be largely circumvented if weight is determined in conjunction with a thoughtful gross and microscopic evaluation that includes an estimation of the parenchymal volume affected by pathology.
