Polyol concentrations in the fluid compartments of the human conceptus during the first trimester of pregnancy: maintenance of redox potential in a low oxygen environment.

Polyols are sugar alcohols formed by the reduction of aldoses and ketoses. Production is favored under conditions of low oxygenation, when it may provide an alternative means to production of lactate for regulating the oxidation-reduction balance of pyridine nucleotides. Polyols also act as important organic osmolytes and as precursors of cell membrane components. We measured free sugar and polyol concentrations in matched samples of maternal serum, intervillous fluid, coelomic fluid, and amniotic fluid from normal human pregnancies at 5-12 wk gestational age. The concentrations of fructose, inositol, sorbitol, erythritol, and ribitol were significantly higher in coelomic and amniotic fluids than in maternal serum, but the reverse was the case for glucose and glycerol. Intervillous fluid concentrations of inositol, mannitol, and sorbitol were also significantly higher than those in maternal serum. These results demonstrate that the polyol pathway, considered vestigial in adult tissues, is highly active in the human conceptus during early pregnancy. The pathway may serve to maintain ATP concentrations and cellular redox potential while the embryo develops in a low oxygen environment. Polyols may also play important physiological roles in development of the human conceptus, possibly drawing water and solutes across the placenta and expanding the gestational sac.

Uterine glands provide histiotrophic nutrition for the human fetus during the first trimester of pregnancy.

Providing adequate nutrition to the fetus is key to a successful pregnancy. The interstitial form of implantation displayed by the human blastocyst is generally associated with early onset of maternal blood flow to the developing placenta, and hence hemotrophic exchange. However, the recent finding that the maternal intraplacental circulation is not fully established until the third month of gestation suggests that human fetal nutrition may be initially histiotrophic. We therefore investigated activity of the uterine glands during early pregnancy. We demonstrate here that these glands remain active until at least wk 10 of pregnancy, and that their secretions are delivered freely into the placental intervillous space. We also demonstrate phagocytic uptake by the placental syncytiotrophoblast of two glycoproteins, the mucin MUC-1 and glycodelin A, synthesized in the maternal glands. Glycodelin was also detected within the epithelium of the secondary yolk sac lining the exocoelomic cavity, indicating that the yolk sac may play an important role in nutrient exchange before vascularisation of the chorionic villi. Our findings demonstrate that the uterine glands are an important source of nutrients during organogenesis, when metabolism is essentially anaerobic.

Distribution and transfer pathways of antioxidant molecules inside the first trimester human gestational sac.

The first-trimester human placenta has limited antioxidant enzyme capacity. We investigated the distribution and transfer pathways of antioxidant molecules inside the first trimester gestational sac. The coelomic fluid of the exocoelomic cavity, which borders the inside of the first-trimester placenta, contained a very low level of reduced glutathione. Glutathione disulfide was undetectable in most coelomic samples, suggesting that the role of glutathione-related detoxification system is limited in fetal fluid compartments. The coelomic fluid contained similar concentrations of ascorbic and uric acid to maternal plasma. The levels of alpha- and gamma-tocopherol were lower in coelomic fluid, compared with maternal plasma. The presence of these molecules inside the early gestational sac suggests that they may play an essential role in the fetal tissues' antioxidant capacity at a time when the fetus is most vulnerable to oxidative stress. We also demonstrated by immunostaining the presence of alpha-tocopherol transfer protein in the cytoplasm of trophoblastic cells, glandular epithelium of the decidua, and mesothelial layer of the secondary yolk sac. This finding indicates that the uterine glands and the secondary yolk sac play key roles in supplying this essential vitamin to the developing fetus before the placental circulations are established.

The contribution of placental oxidative stress to early pregnancy failure.

In cases of miscarriage, onset of the maternal blood flow to the placenta is precocious and disorganized compared with this event in normal pregnancy. We sought to determine whether this difference is associated with excessive levels of oxidative damage and stress in the placental tissues. Morphological and immunohistochemical markers of cellular stress and damage, including expression of heat shock protein 70, formation of N-Tyr residues, and lipid peroxidation, were increased in tissues obtained from missed miscarriages compared with controls. The effect was greatest in those pregnancies of shorter than 77 days' duration and with evidence of recent fetal demise. It was associated with increased apoptosis and decreased numbers of mitotic cells, indicating that oxidative stress overwhelms cellular antioxidant defense systems. No differences were observed between miscarriages with normal and abnormal karyotypes. The spectrum of villous changes occurring after fetal demise indicates that the duration of placental retention in utero after fetal demise is a critical determinant of villous histology. The causes of many miscarriages remain unclear; however, our findings indicate that placental oxidative stress with resultant damage to the syncytiotrophoblast, secondary to early onset of the maternal circulation, may provide a final common mechanism.

Endometrial glands as a source of nutrients, growth factors and cytokines during the first trimester of human pregnancy: a morphological and immunohistochemical study.

BACKGROUND: The maternal circulation to the human placenta is not fully established until 10-12 weeks of pregnancy. During the first trimester the intervillous space is filled by a clear fluid, in part derived from secretions from the endometrial glands via openings in the basal plate. The aim was to determine the activity of the glands throughout the first trimester, and to identify components of the secretions. METHODS: Samples of human decidua basalis from 5-14 weeks gestational age were examined by transmission electron microscopy and immunohistochemically. An archival collection of placenta-in-situ samples was also reviewed. RESULTS: The thickness of the endometrium beneath the implantation site reduced from approximately 5 mm at 6 weeks to 1 mm at 14 weeks of gestation. The glandular epithelium also transformed from tall columnar cells, packed with secretory organelles, to a low cuboidal layer over this period. The lumens of the glands were always filled with precipitated secretions, and communications with the intervillous space could be traced until at least 10 weeks. The glandular epithelium reacted strongly for leukaemia inhibitory factor, vascular endothelial growth factor, epidermal growth factor, transforming growth factor beta, alpha tocopherol transfer protein, MUC-1 and glycodelin, and weakly for lactoferrin. As gestation advanced uterine natural killer cells became closely approximated to the basal surface of the epithelium. These cells were also immunopositive for epidermal growth factor. CONCLUSIONS: Morphologically the endometrial glands are best developed and most active during early human pregnancy. The glands gradually regress over the first trimester, but still communicate with the intervillous space until at least 10 weeks. Hence, they could provide an important source of nutrients, growth factors and cytokines for the feto-placental unit. The endometrium may therefore play a greater role in regulating placental growth and differentiation post-implantation than previously appreciated.

Comparison of ultrasonographic and Doppler mapping of the intervillous circulation in normal and abnormal early pregnancies.

OBJECTIVE: To assess the value of ultrasonography and Doppler imaging in characterizing the intervillous circulation in normal and abnormal early pregnancy. DESIGN: Cross-sectional study. SETTING: Tertiary care academic hospital. PATIENT(S): Eighty-five normal pregnancies and 125 missed miscarriages at 7 to 13 weeks of gestation. INTERVENTION(S): Grey-scale ultrasonography was used to evaluate the placental anatomy and detect moving echoes inside the intervillous space, and color power Doppler imaging was used to detect continuous venous-like flow in the placental tissue. MAIN OUTCOME MEASURE(S): Degree of agreement between two investigators for use of grey-scale imaging, comparison of detection of moving echoes in normal and abnormal pregnancies, and comparison of detection of intervillous circulation with grey-scale and color Doppler imaging in abnormal pregnancies. RESULT(S): The overall degree of agreement between the two investigators was good. A significantly different distribution of blood flow was found between normal and abnormal pregnancies at 7 to 9 weeks and 10 to 11 weeks but not at 12 to 13 weeks. Intervillous moving echoes were detected by grey-scale imaging significantly more frequently than an intervillous blood flow was detected with color Doppler imaging. CONCLUSION(S): In early pregnancy failure, there is a premature and diffuse onset of intervillous blood flow that can be detected by grey-scale imaging. This abnormal blood flow pattern may increase the oxidative stress on the early placental tissue and subsequently impair placental development.

Relationship among maternal serum endocrinology, placental karyotype, and intervillous circulation in early pregnancy failure.

OBJECTIVE: To evaluate the relationship among maternal serum endocrinology, placental karyotype, and intervillous blood flow in missed miscarriage. DESIGN: Cross-sectional study of maternal serum, transvaginal ultrasound/Doppler, and placental cytogenetic and immunohistochemical investigations. SETTING: Tertiary care academic hospital. PATIENT(S): One hundred fifty-two women with missed miscarriage between 7 and 13 weeks of gestation. INTERVENTION(S): Ultrasound features, placental intervillous circulation findings on color Doppler imaging, and maternal serum level of alpha-fetoprotein (AFP), beta-hCG, E(2), P, and inhibin A were compared retrospectively with placenta karyotype and hCG immunochemistry. MAIN OUTCOME MEASURES: Data were analyzed according to karyotype results, presence or absence of an intervillous circulation, and delay between fetal demise and evacuation. RESULT(S): The presence of intervillous blood flow and serum concentrations of the different hormones were independent of placental karyotype. Serum beta-hCG and P were significantly higher in cases with intervillous blood flow. No difference in immunostaining for beta-hCG was found between placental tissues from normal pregnancies and missed miscarriages, but significantly higher villous beta-hCG content was found on Western blotting in miscarriage with a recent fetal demise. CONCLUSION(S): The excessive entry of maternal blood inside the placenta in the early stage of most miscarriages is unrelated to conceptus karyotype, and hCG features may reflect a temporary attempt of the trophoblast to stabilize after the initial oxidative insult.

Oxygen, early embryonic metabolism and free radical-mediated embryopathies.

Free radicals, once the preserve of chemists, are now recognized as playing a central role in many biological systems. They are formed as an inevitable by-product of aerobic respiration and various cytoplasmic processes at a rate dependent upon the prevailing oxygen tension. At physiological concentrations, oxygen and nitrogen free radical species play key roles in intracellular signalling, regulating many homeostatic mechanisms and mediating stress responses. If concentrations exceed cellular defences, however, then indiscriminate damage may occur to lipids, proteins and DNA. Cell function may be perturbed, and in the most severe cases apoptosis may result. Although there are significant species differences, many aspects of early mammalian development, from fertilization through to differentiation of the principal organ systems, take place in vivo in a low oxygen environment. This may serve to protect the embryo from free radical damage, for exposure of early embryos to ambient oxygen concentrations or the products of maternal metabolic disorders is often associated with reduced viability and an increased rate of congenital malformations. Administration of free radical scavengers, including vitamins C and E, can mitigate many of these effects, indicating the importance of a balanced maternal diet to successful reproduction.

Trophoblastic oxidative stress in relation to temporal and regional differences in maternal placental blood flow in normal and abnormal early pregnancies.

Onset of the maternal-placental circulation was studied by Doppler ultrasonography in 65 pairs of age-matched normal and abnormal pregnancies. In normal pregnancies intervillous blood flow increased with gestational age, being detected in 9 of 25 cases at 8 to 9 weeks but in 18 of 20 at 12 to 13 weeks (P = 0.001). By contrast, in abnormal pregnancies flow was detected in nearly all cases (22 of 25) at 8 to 9 weeks (P < 0.001). In addition, regional differences were observed between the groups. Early flow was restricted to the peripheral regions of most normal placentas (P < 0.001), whereas in missed miscarriages it was most common in central regions or throughout the placenta (P < 0.05 and P < 0.001, respectively). Immunoreactivity for heat shock protein 70 and nitrotyrosine residues was greater in samples from peripheral than from central regions of normal placentas (P = 0.028 and P = 0.019, respectively), and from missed miscarriages compared to controls (P = 0.005 and P = 0.001, respectively). Our results indicate that oxidative damage to the trophoblast, induced by premature and widespread onset of the maternal placental circulation secondary to shallow trophoblast invasion, is a key factor in early pregnancy loss. High oxygen concentrations in the periphery of normal early placentas may similarly induce local regression of the villi, leading to formation of the chorion laeve.