Željka Matašin

Structural changes in the rat placenta during the last third of gestation discovered by stereology

Structural changes in the rat placenta during the last third of gestation were for the first time assessed by stereology. Fischer female rats were euthanized on the day 16 or day 19 of gestation, and 35 placentas were collected. Three randomly selected placentas from each group were stereologically analyzed for the absolute volume. The proportion of the glycogenic cells and the trophoblast giant cells (TGC) in the basal part of the placenta was calculated using volume density. The absolute volume of the rat placenta on the day 16 of gestation was determined as 0.0638 cm3. The labyrinth comprised 0.0274 cm3, the basal plate 0.0271 cm3 and the decidua 0.0093 cm3. On the day 19 of gestation, the absolute volume of the placenta was 0.1627 cm3, the labyrinth occupied 0.0922 cm3, the basal plate 0.0596 cm3 and the decidua 0.0109 cm3. The volume density of trophoblast giant cells was 0.174 cm0 on the day 16 and 0.107 cm0 on the day 19 of gestation. The glycogenic cells comprised 0.379 percentage of the basal plate on the day 16 and 0.236 on the day 19 of gestation. We conclude that the absolute volume of the whole placenta and the labyrinth has increased from day 16 to the day 19 of gestation. In contrast, the volume density of glycogenic cells and trophoblast giant cells was higher on the day 16 than on the day 19 of gestation, probably due to the intensive trophoblast invasion during that time.

Reply to comment on "Structural changes in the rat placenta during the last third of gestation discovered by stereology"

Dear Editor, We are thankful to our colleagues for their interest in our paper and comments that they have provided. We could not agree more with the part of the letter regarding the method of sampling. On the basis of our 16-year-long experience in research on rat placentas, we underline sampling as one of the most important concepts in stereology, especially in the light of biological variability [1]. This variability is the reason why we approach sampling with the greatest care, as it is evident from all our published papers in the field of stereology. In addition, we consider it as one of the best methods for quantification of biological materials. Systematic random sampling, which combines both the unbiasedness of random sampling and the efficiency of a systematic sampling, was used in our research. It is based on the selection of the final sample systematically, while the first sample was selected randomly within the first sampling interval [2]. Sections were sampled at a ratio 1:10 (Section Sampling Fraction-SSF), with a random section (RS) selection from the first ten sections (in this case, the 3rd section) and then every 10th section after this initial selection. Preliminary measurements were performed for each of the experimental groups. In addition, due to its small size, it is possible to analyze the entire section of the rat placenta as a single field, which we did, as seen in Figure 2 [3]. However, this is not possible for human placenta, which, due to its larger size, cannot fit into a single section or single field for stereological analysis.