Regional anatomy of the term human placenta

Unveiling Distribution of Per- and Polyfluoroalkyl Substances in Matched Placenta-Serum Tetrads: Novel Implications for Birth Outcome Mediated by Placental Vascular Disruption

The placenta is pivotal for fetal development and maternal-fetal transfer of many substances, including per- and polyfluoroalkyl substances (PFASs). However, the intraplacental distribution of PFASs and their effects on placental vascular function remain unclear. In this study, 302 tetrads of matched subchorionic placenta (fetal-side), parabasal placenta (maternal-side), cord serum, and maternal serum samples were collected from Guangzhou, China. Eighteen emerging and legacy PFASs and five placental vascular biomarkers were measured. Results showed that higher levels of perfluorooctanoic (PFOA), perfluorooctane sulfonic acid (PFOS), and chlorinated polyfluorinated ether sulfonic acids (Cl-PFESAs) were detected in subchorionic placenta compared to parabasal placenta. There were significant associations of PFASs in the subchorionic placenta, but not in the serum, with placental vascular biomarkers (up to 32.5%) and lower birth size. Birth weight was negatively associated with PFOA (β: -103.8, 95% CI: -186.3 and -21.32) and 6:2 Cl-PFESA (β: -80.04, 95% CI: -139.5 and -20.61), primarily in subchorionic placenta. Mediation effects of altered placental angiopoietin-2 and vascular endothelial growth factor receptor-2 were evidenced on associations of adverse birth outcomes with intraplacental PFOS and 8:2 Cl-PFESA, explaining 9.5%-32.5% of the total effect. To the best of our knowledge, this study is the first to report on differential intraplacental distribution of PFASs and placental vascular effects mediating adverse birth outcomes and provides novel insights into the placental plate-specific measurement in PFAS-associated health risk assessment.

Pilot study of placental tissue collection, processing, and measurement procedures for large scale assessment of placental inflammation

Background

Placental dysfunction is related to many pregnancy complications, but collecting placental specimens for investigation in large scale epidemiologic studies is often infeasible. Standard procedures involving immediate collection after birth and snap freezing are often cost prohibitive. We aimed to collect pilot data regarding the feasibility and precision of a simpler approach, the collection of tissue samples following 24 hours of refrigeration of whole placentae at 4°C, as compared to the “gold standard” of snap freezing excised tissue within 40 minutes of delivery for the assessment of inflammatory cytokines.

Methods

Placentae were collected from 12 women after delivering live-born singleton babies via uncomplicated vaginal delivery. Two placentae were utilized to establish laboratory tissue processing and assay protocols. The other 10 placentae were utilized in a comparison of three tissue collection conditions. Specifically, key inflammatory cytokines were measured in 3 sections, representing three collection conditions. Sections 1 (full thickness) and 2 (excised prior to freezing) were obtained within 40 minutes of delivery and snap frozen in liquid nitrogen, and section 3 (full thickness) was obtained after refrigerating the placenta at 4°C for 24 hours.

Results

IL-6, IL-10, and IL-8 all had comparable concentrations and variability overall in all three section types. Levels of tumor necrosis factor alpha (TNF-α) were too low among samples to reliably measure using immunoassay.

Conclusions

Refrigeration of placentae prior to processing does not appear to compromise detection of these cytokines for purposes of large scale studies. These findings provide a framework and preliminary data for the study of inflammatory cytokines within the placenta in large scale and/or resource-limited settings.

Analytical theory of oxygen transport in the human placenta

We propose an analytical approach to solving the diffusion-convection equations governing oxygen transport in the human placenta. We show that only two geometrical characteristics of a placental cross-section, villi density and the effective villi radius, are needed to predict fetal oxygen uptake. We also identify two combinations of physiological parameters that determine oxygen uptake in a given placenta: (i) the maximal oxygen inflow of a placentone if there were no tissue blocking the flow and (ii) the ratio of transit time of maternal blood through the intervillous space to oxygen extraction time. We derive analytical formulas for fast and simple calculation of oxygen uptake and provide two diagrams of efficiency of oxygen transport in an arbitrary placental cross-section. We finally show that artificial perfusion experiments with no-hemoglobin blood tend to give a two-orders-of-magnitude underestimation of the in vivo oxygen uptake and that the optimal geometry for such setup alters significantly. The theory allows one to adjust the results of artificial placenta perfusion experiments to account for oxygen-hemoglobin dissociation. Combined with image analysis techniques, the presented model can give an easy-to-use tool for prediction of the human placenta efficiency.

Stereological analysis of terminal villi of the placentas of pregnant woman with sideropenic anemia

Iron deficiency, causing maternal sideropenic anemia, is one of the most frequent nutritive disorder that develops during the pregnancy. We collected 30 placentas from anemic mothers and 30 placentas from mothers belonging to the control group. Terminal villi (magnification 10x) and terminal villi capillaries (magnification 40x) were stereologically analyzed and numerically determined.In the placentas from anemic mothers we noted the values a) terminal villi: volume density 0,43 mm0, surface density 24.13 mm-1, total volume 185.57 cm3 and total surface 10.27 m2; b) capillaries of terminal villi: volume density 0.53 mm0 and total volume 224.18 cm3. In the placentas from mothers belonging to the control group we observed the following values a) terminal villi: volume density 0.44 mm0, surface density 22.27 mm-1, total volume 200.17 cm3 and total surface 10.15 m2; b) capillaries of terminal villi: volume density 0.42 mm0 and total volume 197.00 cm3. Compared with the control group anemic mothers' placentas have a significant higher values of surface density of terminal villi (p<0.05), volume density (p <0.01) and absolute volume (p<0.0001) of terminal villi capillaries, and significant lower values of absolute volume of terminal villi (p<0.05).In anemic mothers' placentas, the total volume of terminal villi changes disproportionately to the total surface of terminal villi with statistically significant increase of terminal villi capillaries compared with control group. 

Cluster analysis of placental inflammatory proteins can distinguish preeclampsia from preterm labor and premature membrane rupture in singleton deliveries less than 28 weeks of gestation

PROBLEM

Inflammation within the preterm placenta is common and leads to adverse outcomes for premature infants. The risks of complications are different between iatrogenic (e.g. PE) and spontaneous (e.g. PL and membrane rupture) causes of preterm delivery, suggesting different underlying biology contributes to these placental conditions.

METHOD OF STUDY

Thirty preterm singleton placentas from the following groups were analyzed: (i) severe PE, (ii) preterm premature membrane rupture (pPROM), and (iii) PL. Proinflammatory and anti-inflammatory cytokines, adhesion and angiogenic molecules were measured in placental lysates using a multiplex assay. K-means cluster analysis was used to generate patterns of protein level intensity.

RESULTS

Three cluster patterns were apparent. Placentas from PE had high levels of vascular endothelial growth factor (VEGF) combined with low levels of acute inflammatory proteins (IL-1β, IL-18, IL-6, TNF-α), low IL-1 RA, and high transforming growth factor β (TGF-β). PL and pPROM had higher anti-inflammatory IL-1 RA and thrombomodulin combined with lower VEGF, regardless of proinflammatory cytokines and adhesion molecules. Half of the PL and pPROM cases had clusters of heightened inflammatory responses (lower TGF-β clustered with higher intensity of inflammatory mediators).

CONCLUSION

Discriminating protein patterns were elucidated and may serve as a foundation from which to understand the biologic mechanisms underlying these pregnancy complications.

Taking tissue samples from the placenta: an illustration of principles and strategies

Tissue samples are removed from placentas for a variety of reasons associated with a host of investigative techniques, including chorionic villus sampling, villus explant culture, cell culture, proteomic analysis, gene expression profiling, microscopy and morphometry. Apart from the latter, especially stereological analysis, many studies provide extremely limited information on how the samples were selected. At worst, we learn little more than the placenta was sampled. Sometimes, studies provide sufficient detail to reveal flaws in sampling, e.g. the selection of placentomes based on size rather than mere presence. Occasionally, the reader is informed, without further explanation, that representative samples were taken or that samples from placentas in different study groups were taken from standard or similar sites. Such statements raise doubts about the unbiasedness of the sampling process, leave the reader in ignorance of the quality of the final sample, thwart attempts at achieving study repeatability and compromise interpretations of the validity of study outcomes. And yet study outcomes depend critically on the selection process because sampling influences study errors, notably precision (random error) and bias (systematic error). This article aims to review the basic principles and virtues of random sampling in general and the practical utilities of variants of it. For many functional and structural studies, it suffices to randomise the positions of tissue samples but, in certain structural studies, orientation must also be randomised. Therefore, sampling tools for stereological estimation of membrane surface areas, tubule lengths and layer thicknesses are mentioned. Although emphasis is accorded to the placenta, the principles apply equally well to other organs and to lower levels of organisation including the subcellular. It is hoped that this review will inform future study designs, encourage greater transparency and facilitate sampling improvements.

Monocarboxylate transporter 8 expression in the human placenta: the effects of severe intrauterine growth restriction

Thyroid hormones (THs) are essential for normal fetal development, with even mild perturbation in maternal thyroid status in early pregnancy being associated with neurodevelopmental delay in children. Transplacental transfer of maternal THs is critical, with increasing evidence suggesting a role for 3,3',5-tri-iodothyronine (T3) in development and function of the placenta itself, as well as in development of the central nervous and other organ systems. Intrauterine growth restriction (IUGR) is associated with fetal hypothyroxinaemia, a factor that may contribute to neurodevelopmental delay. The recent description of monocarboxylate transporter 8 (MCT8) as a powerful and specific TH membrane transporter, and the association of MCT8 mutations with profound neurodevelopmental delay, led us to explore MCT8 expression in placenta. We describe the expression of MCT8 in normal human placenta throughout gestation, and in normal third-trimester placenta compared with that associated with IUGR using quantitative reverse transcriptase PCR. MCT8 mRNA was detected in placenta from early first trimester, with a significant increase with advancing gestation (P=0.007). In the early third trimester, MCT8 mRNA was increased in IUGR placenta compared with normal samples matched for gestational age (P<0.05), but there was no difference between IUGR and normal placenta in the late third trimester. Western immunoblotting findings in IUGR and normal placentae were in accord with mRNA data. MCT8 immunostaining was demonstrated in villous cytotrophoblast and syncytiotrophoblast as well as extravillous trophoblast cells from the first trimester onwards with increasingly widespread immunoreactivity seen with advancing gestation. In conclusion, expression of MCT8 in placenta from early gestation is compatible with an important role in TH transport during fetal development and a specific role in placental development. Altered expression in placenta associated with IUGR may reflect a compensatory mechanism attempting to increase T3 uptake by trophoblast cells.

A stereologic study of postmature placentas fixed by dual perfusion

OBJECTIVE

Placental insufficiency has been considered the cause of increased morbidity in infants delivered postmaturely. Former quantitative studies have indicated a decrease in some placental structures just before term. In this study we describe a method of dual perfusion fixation to provide tissue for stereologic examination. Postmature placentas were examined with this method.

STUDY DESIGN

Eleven postmature placentas and 14 placentas delivered at term were fixed by dual perfusion. The volume and the surface area of villi, the trophoblast volume, and the volume, surface area, and length of villous capillaries were estimated by stereologic examination. The Mann-Whitney test (p < or = 0.05) was used for statistical analysis.

RESULTS

Morphologic features were normal in all placentas. No significant differences were disclosed in the stereologic estimates of placentas delivered at term and postmature placentas.

CONCLUSION

No morphologic or significant quantitative changes were found in postmature placentas.

Placental morphometry using a computer assisted measuring programme: reference values for normal pregnancies at term

Using the principle that the human placenta is anatomically composed of fetomaternal flow units, we developed a computer-assisted measurement programme capable of recording complex histometric data about the characteristics of the maturation and structural differentiation of resorption villi, as well as subjecting the results to simultaneous statistical processing. Using 42 placentas obtained after normal pregnancies, reference values were derived for the five primary geometrical and six further arithmetical parameters. From these findings, we also calculated the total resorption villi surface area, the proportion of this surface area occupied by epithelial plates, and the resorption-villi surface are relative to the birth weight of the child. Our findings are compared with other available results, and the reasons for discrepancies between previously published measurements are discussed.

Perfusion fixation for placental morphologic investigation

Fifty placentas were collected after vaginal delivery or cesarean section from normal and abnormal pregnancies and were fixed under different conditions of perfusion using a peristaltic roller pump. In each case a physiologic-heparin perfusate was used for less than 10 minutes, followed by a buffered solution of glutaraldehyde-formaldehyde. The best results were obtained with placentas from cesarean sections perfused immediately after delivery with a pressure maintained under 60 mm Hg. Placentas of this group were fixed within 30 minutes and electron microscopy demonstrated good preservation of cellular ultrastructure. Perfusion fixation could be performed up to 6 hours after delivery with satisfactory histologic results. In these cases, electron microscopy revealed ischemic changes 10 minutes after delivery and severe necrosis 1 hour after delivery. When the perfusion pressure was maintained over 60 mm Hg, diffuse damage of the villous morphology was observed. Histomorphometric analysis showed significant differences between terminal villi from nonperfused (immersed-fixed) placentas and perfused-fixed placentas. The mean barrier and trophoblastic thicknesses and the mean volume fraction of trophoblast were significantly (P less than .001) increased in the nonperfused group compared with the perfused group.

Stereological re-examination of the effects of varying oxygen tensions on human placental villi maintained in organ culture for up to 12 h

The effects of exposure to various oxygen tensions on villi in organ culture are re-examined. Villi from ten normal mature placentae were cultured under hypoxic (6 per cent oxygen) and hyperoxic (40 per cent oxygen) conditions for 6 or 12 h. Control tissue (zero time in culture) was also taken. Pieces of tissue were fixed by immersion and embedded in resin for semithin sectioning. Systematically sampled microscopical fields were analysed stereologically to estimate harmonic and arithmetic mean thicknesses for the trophoblast and for the villous membrane and to assess the volumetric composition and mean diameter of villi. Trophoblast thicknesses were influenced significantly by oxygen tension, being smaller in hypoxic and greater in hyperoxic media. No significant interaction terms or effects of time in culture were detected. Villous membrane thicknesses altered in a similar fashion to trophoblast thicknesses. No significant differences in the composition of villi were detected but villi tended to be greater in diameter during hyperoxia. Findings are discussed in the context of previously reported adaptations in vivo, in different regions of the placental lobule and during chronic maternal hypoxic stress at high altitude. We conclude that there is insufficient evidence to support the claim that villi can adapt in vitro to varying ambient oxygen tensions.

Methodological problems in placental morphometry: apologia for the use of stereology based on sound sampling practice

Several problem areas in morphometry of human and animal placentae are reviewed. Attention is given to methods of tissue processing (handling, mode of fixation, embedding, shrinkage) and sampling (of organs, tissue blocks, sections, micrographs). Principal sources of bias and sampling variability are identified and the crucial importance of randomized sampling is emphasized. Methods for obtaining structural quantities from sections are compared. The case is made for estimating absolute values (volumes, surface areas, lengths, numbers, thicknesses) using stereological principles rather than relying on planar data (profile areas, perimeter lengths, numbers, apparent thicknesses). Absolute values may be obtained simply and efficiently without resort to expensive measuring devices. Finally, morphological descriptors suitable for correlating with functional data or for comparing normal and diseased organs are surveyed.

Regional variations in the levels of zinc, iron, copper, and calcium in the term human placenta

This study investigated the influence of the location of the sampling site during elemental analyses of 21 human term placentae. The levels of iron, zinc, copper and calcium in fetal membranes, umbilical cords and placental discs were measured by atomic absorption spectrophotometry and compared. The disc samples were obtained from central (peri-insertion and mid-disc fetal and maternal halves), and peripheral regions. Significant variations were found. Copper was present in highest levels (17.2 +/- 2.0 micrograms/g dry weight) in the fetal membranes. Calcium levels were highest (712 +/- 47 micrograms/g dry weight) in the periphery of the placental disc. Iron levels were highest (558 +/- 14 micrograms/g dry weight) in the central regions of the disc. Zinc levels were lower (50.3 +/- 1.4 micrograms/g dry weight) in the fetal half of the mid-disc regions than in the maternal half (56.0 +/- 1.2 micrograms/g dry weight). This study demonstrates the importance of defining the location of the sampling site in studies involving elemental analysis of the placenta.