Vasculosyncytial membranes are unique structures of the human placenta , which include the apposition of the trophoblasts (synctio- and cyto-) with the fetal chorionic villous endothelium (Figure 1). These structures are essential for the normal oxygen and nutrient exchange between the maternal and fetal circulations. The formation of the vasculosyncytial membranes is part of normal development of the human placenta and is specifically referred to as villous tree maturation. Defective villous tree maturation can lead to deficient vasculosyncytial membranes that, in turn, have been implicated in nutritional disorders such as fetal growth restriction, respiratory failure of the placenta or fetal hypoxia. We previously reported that 20.7% of placentas of structurally normal cases of fetal death have delayed villous maturation, a condition in which there is insufficient development of the terminal villi, reduced vascularization of the chorionic villi and deficiency of vasculosyncytial membranes .
Chronic fetal hypoxemia can stimulate production and secretion of erythropoietin . As erythropoietin does not cross the placenta and is not stored, increased fetal plasma or amniotic fluid concentrations of this hormone is considered to reflect chronic fetal hypoxemia. The current study was designed to determine whether delayed villous maturation is associated with changes in amniotic fluid erythropoietin concentrations.
This was a retrospective observational study of singleton pregnant women without pre-eclampsia, gestational hypertension, abruption or gestational diabetes mellitus who (a) underwent an elective cesarean section at 37–42 weeks of gestation; (b) had amniotic fluid retrieved at the time of cesarean delivery; (c) had a live-birth newborn; (d) had a placental histologic examination at Hutzel Women’s Hospital, Detroit, MI, USA; and (e) provided written informed consent and agreed for such information to be used for research purposes. Controls (n=61) were pregnancies without villous maturation abnormalities, and cases (n=5) were pregnancies with delayed villous maturation. The collection of data was approved by the Human Investigation Committee of Wayne State University.
Placental histologic examination was performed using hematoxylin and eosin and CD-15 immunohistochemistry by a perinatal pathologist (SJ) blinded to clinical information, except gestational age at delivery. Histologic assessment of delayed villous maturation was made by the presence of a monotonous immature villous population (at least 10 such villi), constituting up to at least one-third of the sampled villi, with (a) substantially more villous stroma; (b) more centralized vessels; (c) fewer and less well-formed vasculosyncytial membranes than that of normal pregnancy for gestational age; (d) recapitulation of the histology of early pregnancy;  and (e) CD-15 positivity . Accelerated villous maturation cannot be ascertained in placentas delivered at term .
Amniotic fluid erythropoietin concentrations were measured using a commercially available specific immunoassay [American Laboratory Products Company (ALPCO), Salem, NH, USA]. The sensitivity of the assay was 1.8 mIU/mL, and coefficients of variation for intra- and inter-assays were 6.1% and 9.2%, respectively. For statistical analysis, a result that was below the limit of detection was replaced by 99% of the minimum observed value.
(1) Concentrations of erythropoietin in the amniotic fluid were measurable only in 41% (25/61) of controls (25th percentile and 50th percentile of amniotic fluid erythropoietin were less than the limit of detection; 75th percentile of amniotic fluid erythropoietin=4.2 mIU/mL). (2) Patients who had delayed villous maturation (n=5) had a significantly higher concentration of amniotic fluid erythropoietin than those in the control group (n=61) (Wilcoxon rank sum test P-value=0.048) (Figure 2).
This study is the first to demonstrate that delayed villous maturation is associated with higher concentrations of amniotic fluid erythropoietin than the absence of these lesions. This observation suggests that the structural abnormalities in the vasculosyncytial membranes may lead to impaired exchange and fetal hypoxemia in a fraction of the cases.
Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.
Research funding: This research was supported, in part, by the Perinatology Research Branch, Division of Obstetrics and Maternal-Fetal Medicine, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, U.S. Department of Health and Human Services (NICHD/NIH/DHHS); and, in part, with Federal funds from NICHD/NIH/DHHS under Contract No. HHSN275201300006C.
Employment or leadership: Dr. Romero has contributed to this work as part of his official duties as an employee of the United States Federal Government.
Competing interests: The funding organization(s) played no role in the study design; in the collection, analysis, and interpretation of data; in the writing of the report; or in the decision to submit the report for publication.
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