PLACENTAL DEVELOPMENT IN THE DOMESTIC CAT: HISTOLOGICAL AND ULTRASOUND INVESTIGATION

In spite of comprehensive placental classification, no exhaustive studies of placental development during different stages of pregnancy in the Domestic Cat are present in literature. The aim of this study was to evaluate placental histological changes in relation to ultrasound appearance during the course of the entire pregnancy. Thirty-five pregnant queens were recruited for this study. Pregnancy was previously confirmed by ultrasound evaluation using a linear probe 7-10 Mhz. Date of mating was not noted. Pregnancy data was estimated through specific parameters according to the study of Zambelli et al. (2002) [1]: gestational sac diameter and total length of chorionic vesicles for early stages; crown-rump length of fetus for older stages. All the queens underwent ovariohysterectomy and once the uteri were removed, morphologic assessments were recorded before fixation in 10% neutral buffered formalin solution. Samples were processed after embedding in paraffin, stained with E&O Standard Staining Protocol and 5μm thick-sections were microscopically analysed. Queens were divided in six groups according to pregnancy data: Group A (n=5) pre-contact phase; Group B (n=6) 15-19 days post coitum (p.c.); Group C (n=9) 20-29 days p.c.; Group D (n=3) 30-39 days p.c.; Group E (n=7) 40-49 days p.c.; Group F (n=5) 50-60 days p.c. The ultrasound uterine evaluation has provided useful information of gestational age even before the placenta develops. Placental ultrasound appearance does not undergo noteworthy modifications during the entire course of pregnancy. At the histological examination the endometrium shows a highly proliferative activity even before contact with trophoblast occurs. The process leading to placental development is carried out gradually and the placenta shows marked morphological changes according to fetal development. Histologically, three overlapping layers forms the placental thickness: the most relevant zone is lamellar; below there is the junctional zone at the level of which detachment from the endometrial glandular layer takes place during parturition. The most significant histological events occur into the lamellar zone. In a limited group of samples (15%) multiple foci of mineralization have been found into the lamellar zone. The latter have never been outlined for the queen so far. Comparable findings have been described and identified as placental calcification in human and mouse placenta [2,3]. Further studies and specific staining procedures are required to determine their origin and role. In conclusion the placenta is an evolving organ that adapts gradually to the growing demands of foetus. Ultrasonography can be considered a useful tool for monitoring pregnancy and placenta developments in the Domestic Cat as well as maternofetal blood flows. Histological examinations allow identification of events like calcification and other modifications occurring during the placental growth