Morphometric studies of fetal placental stem arteries in hypertensive disorders ('toxaemia') of pregnancy

Placental morphometrical and histopathology changes in the different clinical presentations of Hypertensive Syndromes in Pregnancy

OBJECTIVE

Even though there are clinical studies emphasizing the diagnosis and the perinatal intercurrent diseases of the Hypertensive Syndromes in Pregnancy, few of these studies establish the clinical forms of the specific hypertensive syndromes with the associated morphological placental alterations. The lack of studies on placental morphology and the etiopathogenesis of the different clinical standards for HSP, together with the need to objectively characterize these morphological placental lesions justify this study.

STUDY DESIGN

A retrospective study was carried out with 91 placentas examined throughout the period from 2000 to 2003. All placentas from patients presenting HSP in this period were included in the study. These were classified according to features well established by the literature such as laboratory and clinical criteria into: gestational hypertension (GH), chronic hypertension (CH), pre-eclampsia (PE) and pre-eclampsia superimposed on chronic hypertension (PSCH).

RESULTS

The number of knots presented a positive correlation with the length of time and severity of the hypertension during gestation (Spearman correlation: 0.253; P = 0.0158). The fibrin deposit was greater in all HSP groups but the pattern of distribution changes in the most severe cases from perivillous to intravillous as in the PSCH group (P = 0.002). There was no statistically significant difference in the area of the stem vessel walls among the groups. The cases with PE and CH presented a larger number of terminal villi vessels (P < 0.001).

CONCLUSION

This report suggests, that although they could be different types of hypertension or an evaluation of the same disease, the final pathway that leads to microscopic lesions in the placenta is the same, with only different intensity due to the severity of the disease.

Development of the placental villous tree and its consequences for fetal growth

Co-ordinated development of the fetal villous tree of the placenta is necessary for continued fetal growth and well-being. Before fetal viability, blood vessel development within the developing immature intermediate villi (IIV) is characterized by branching angiogenesis, such that the placenta expands to produce 10-16 generations of stem villi. Once fetal viability is attained, a developmental switch occurs to form large numbers of gas-exchanging terminal villi (TV) by non-branching angiogenesis in mature intermediate villi (MIV). Several growth factors, including vascular endothelial growth factor (VEGF), placenta growth factor (PlGF), angiopoietins, and angiostatins are produced within the villi and act locally, via their receptors, to control angiogenesis. Their relative contributions to placental vascular development are not fully understood at the present time. Severe early-onset intrauterine growth restriction (IUGR) is characterized by absent/reversed end-diastolic flow velocity (ARED) in the umbilical arteries, leading to fetal hypoxia, acidosis and a substantial rise in perinatal mortality and morbidity. The placentas from such cases show a deficit in peripheral villous development, which may be perpetuated by the effects of oxygen (delivered by maternal blood into the intervillous space) upon VEGF-directed angiogenesis, the so-called 'placental hyperoxia' theory of villous maldevelopment. Trophoblast apoptosis is a significant feature of early-onset IUGR and may explain poor flow-independent transfer of nutrients to the fetus. Finally, since transgenic mouse studies highlight the importance of trophoblast-derived transcription factors for placental villous (labyrinth) development, it is possible that the villous trophoblast controls the orderly development of the underlying mesoderm and blood vessels into the fetal villi.

Computerized microscope morphometry of umbilical vessels from pregnancies with intrauterine growth retardation and abnormal umbilical artery Doppler

Computerized microscope morphometry was used to study cross sections from the vessels of the umbilical cord in placentas of patients with intrauterine growth retardation (IUGR) that displayed either normal or abnormal umbilical arteries (UA) Doppler flow velocity waveforms (FVW). Cords from 63 eutrophic fetuses with normal Doppler (controls), 47 IUGR fetuses with normal Doppler and 32 IUGR fetuses with abnormal Doppler underwent morphometric analysis using a highly optimized microscope environment (HOME) and "CordHOME" software. IUGR with an accompanying normal Doppler versus control showed a reduction of Wharton jelly and both the total and lumen vein areas. IUGR with an accompanying pathological Doppler showed a comparable reduction in wall thickness and areas of every vessel. These findings indicate that the hypoplastic umbilical vessels are associated with an increase in placental vascular resistance that may be the consequence of underdevelopment in response to a chronic reduction in placental blood flow.

Classification of human placental stem villi: review of structural and functional aspects

The stem villi of the human placenta represent the central branches of the villous trees. They are characterized by a condensed fibrous stroma in which the fetal arteries and veins as well as the arterioles and venules are embedded. Functionally they are accepted as the mechanically supporting structures of the villous trees, and they are supposed to control fetal blood flow to the maternofetal exchange area, which is located in the peripheral villi. To obtain further insights into the functions of the stem villi, the recent literature has been reviewed, and some immunohistochemical, ultrastructural, and reconstruction studies have been added. These new studies were aimed at identifying immunohistochemically different subtypes of stem villi, their branching patterns, the distribution of macrophages, the stromal proliferation patterns, and the differentiation of extravascular stromal cells. Our findings demonstrate that the stem villi and their precursors, the immature intermediate villi, can selectively be identified by anti-gamma-smooth muscle (sm) actin staining. Furthermore, the existence of three different subtypes of stem villi is shown; these differ regarding the presence and distribution of gamma-sm actin-positive cells. These cells were immunohistochemically and ultrastructurally identified as smooth muscle cells and myofibroblasts. Increasingly complex coexpression patterns of cytoskeletal proteins reflect a clearly defined differentiation gradient of extravascular stromal cells, which covers the whole range of an undifferentiated germinative layer beneath the trophoblast to highly differentiated myofibroblasts surrounding the medias of the stem vessels. Possible functions of the extravascular contractile system include the regulation of villous turgor and the control of intervillous blood flow impedance.

Color Doppler flow patterns and flow velocity waveforms of the intraplacental fetal circulation in growth-retarded fetuses

OBJECTIVE

We examined intraplacental color Doppler flow patterns and spectral Doppler flow velocity waveforms of villous arteries in pregnancies with intrauterine growth retardation.

STUDY DESIGN

A total of 192 uncomplicated pregnancies and 29 pregnancies with intrauterine growth retardation between 26 and 41 weeks' gestation were examined in this cross-sectional study. Intraplacental color Doppler flow findings and pulsatility indexes of umbilical and villous arteries were correlated with the presence of intrauterine growth retardation and multiple outcome variables. Villous arteries were identified by their intraplacental color Doppler flow image, and flow velocity waveforms were obtained by superimposition of pulse-wave Doppler.

RESULTS

(1) Intraplacental color Doppler flow signals from two or more villous arteries were detected in all 192 normal pregnancies but were undetectable in 8 of 29 fetuses with intrauterine growth retardation (27.6%, p < 0.0001). Absence of intraplacental color Doppler flow signals was associated with fetal distress in 6 of 8 cases (87.5%) and perinatal death in two cases (25.0%), compared with 3 of 21 (14.2%, p < 0.005) and 0 of 21 (not significant) cases of intrauterine growth retardation with detectable intraplacental color Doppler flow. Median Apgar scores at 1 minute were 5 and 8 (p < 0.05), respectively, and at 5 minutes were 8 and 8 (not significant), respectively. (2) Umbilical artery flow velocity waveforms were abnormal (> 95th percentile) in 8 of 21 cases of intrauterine growth retardation (38.0%) with detectable intraplacental color Doppler flow, including two cases with reversed end-diastolic flow. In contrast, the corresponding villous artery flow velocity waveforms were abnormal in only 1 of 21 cases (p < 0.04).

CONCLUSION

(1) Failure to detect intraplacental color Doppler flow signals is associated with intrauterine growth retardation and fetal distress. (2) Flow velocity waveforms of detectable villous arteries are usually normal in intrauterine growth retardation, even in the presence of extremely abnormal umbilical artery flow velocity waveforms.

Hypoxia-induced fetoplacental vasoconstriction in perfused human placental cotyledons

Effects of maternal hypoxia on fetoplacental vascular resistance in the human placenta were investigated in an in vitro model in which single anatomic subunits (cotyledons) from term placentas were perfused at constant flow through both fetal and maternal circuits by means of a physiologic salt solution containing dextran. Acute reduction of oxygen tension in the maternal perfusate induced prompt fetoplacental vasoconstriction that recovered rapidly on restoration of oxygen to the perfusate. The response, hypoxic fetoplacental vasoconstriction, could be repeatedly demonstrated in the same cotyledon. The time course of hypoxic fetoplacental vasoconstriction was inversely related to oxygen tension of maternal arterial and maternal and fetal venous perfusates. Maternal and fetal venous perfusate pH and PCO2 did not change during the response. It is concluded that hypoxic fetoplacental vasoconstriction is triggered by decreased oxygen availability. It is suggested that hypoxic fetoplacental vasoconstriction may play a role in local regulation of human fetoplacental blood flow in vivo and may contribute to poor fetal prognosis in preeclampsia.

Computerized ultrasonic image analysis for placental characterization in normal and hypertensive pregnancies

A technique has been developed for characterizing ultrasonic images of the human placenta by computerized image analysis. An ultrasonic image data base has been assembled from routine obstetric scans collected from 112 patients. A region within the placenta was manually identified in each image, and a series of parameters which mathematically describe the image texture in the region of interest was calculated. Our pilot study has shown that gestational age at scan, placental position and the presence or absence of hypertension can all be correlated with the mathematically defined textural descriptors of the ultrasonic placental image.