Doppler flow velocity waveforms of the umbilical arteries correlate with intravillous blood volume

Intra-uterine growth restriction is associated with increased apoptosis and altered expression of proteins in the p53 pathway in villous trophoblast

Intrauterine growth restriction (IUGR) affects 3-8% of pregnancies and is associated with altered cell turnover in the villous trophoblast, an essential functional cell type of the human placenta. The intrinsic pathway of apoptosis, particularly p53, is important in regulating placental cell turnover in response to damage. We hypothesised that expression of proteins in the p53 pathway in placental tissue would be altered in IUGR. Expression of constituents of the p53 pathway was assessed using real-time PCR, Western blotting and immunohistochemistry. p53 mRNA and protein expression was increased in IUGR, which localised to the syncytiotrophoblast. Similar changes were noted in p21 and Bax expression. There was no change in the expression of Mdm2, Bak and Bcl-2. The association between altered trophoblast cell turnover in IUGR and increased p53 expression is reminiscent of that following exposure to hypoxia. These observations provide further insight into the potential pathogenesis of IUGR. Further research is required to elicit the role and interactions of p53 and its place in the pathogenesis of IUGR.

Endothelin-1 and leptin as markers of intrauterine growth restriction

OBJECTIVE

To explore the role of endothelin-1 (ET-1) and leptin in intrauterine growth restriction (IUGR) among preeclamptic and non-pre-eclamptic women.

METHODS

Forty three patients with a pregnancy complicated by IUGR, 23 cases with severe pre-eclampsia and 20 cases of non-pre-eclamptic were enrolled. Control group comprised 15 cases with uncomplicated pregnancy. Blood samples from umbilical artery and maternal venous blood were collected at the time of delivery for analysis of ET-1 and leptin levels. Mode of delivery, birth weight and Apgar score were also recorded.

RESULTS

The mean maternal and fetal ET-1 level was significantly higher in pregnancies complicated by IUGR than in control group. The mean maternal leptin level was significantly higher in pre-eclamptic patients when compared to non-preeclamptic and control groups. Mean fetal leptin level was significantly lower in patients compared to control; however, when fetal leptin corrected to fetal weight, it was insignificantly different in the both groups. E-mail: m. alhaggar@yahoo.co.uk.

CONCLUSION

Maternal plasma ET-1 and leptin correlate with the degree of fetal growth restriction originating from deterioration of placental function. Maternal plasma leptin and ET-1 levels may reflect deterioration in fetal growth.

Evidence for a role of TGF-beta1 in the expression and regulation of alpha-SMA in fetal growth restricted placentae

There is evidence that alpha-smooth muscle actin (alpha-SMA) is a protein that plays a pivotal role in the production of contractile forces and it is induced by transforming growth factor-beta1 (TGF-beta1). We have analysed the expression of alpha-SMA, TGF-beta1, its receptor RI and the activator phospho-Smad2 in (a) fetal growth restriction pre-eclamptic placentae characterised by early onset and absence of end diastolic velocities in the umbilical arteries (FGR-AED) and (b) control placentae accurately matched for gestational age. The study was performed by immunohistochemical, quantitative Western blotting, ELISA, RT-PCR and in vitro analyses. We found that TGF-beta1 stimulates alpha-SMA production in chorionic villi cultured in vitro. In addition, we observed that in vivo TGF-beta1 concentration is significantly higher in FGR-AED placental samples than in control placentae and that this growth factor could have a paracrine action on villous stroma myofibroblasts expressing TGF-beta1 receptors and phospho-Smad2. Indeed, we report that alpha-SMA undergoes a redistribution in FGR-AED placental villous tree, i.e. we show that alpha-SMA is enhanced in medium and small stem villi and significantly decreased in the peripheral villi. Our data allow us to consider TGF-beta1 and alpha-SMA as key molecules related to FGR-AED placental villous tree phenotypic changes responsible for increased impedance to blood flow observable in this pathology.

Endothelin and platelet-activating factor: significance in the pathophysiology of ischemia/reperfusion-induced fetal growth restriction in the rat

OBJECTIVE

The objective of the study was to evaluate the role of endothelin-1 and platelet-activating factor in ischemia/reperfusion-induced fetal growth restriction in the rat.

STUDY DESIGN

On day 17 of gestation, the right uterine and ovarian arteries were occluded for 30 minutes in experimental but not sham-operated rats. All rats received endothelin receptor A antagonist, A-127722 (10 mg/kg per day), platelet-activating factor antagonist, WEB-2086 (1 mg/kg), or vehicle. On gestational day 21, litter size, fetal viability, and fetal and placental weights were recorded. Reverse transcription-polymerase chain reaction for phospholipase A2-IIA and preproendothelin-1 messenger ribonucleic acid was performed on uterus and placentas from each uterine horn. Groups were compared statistically by analysis of variance.

RESULTS

Ischemia/reperfusion reduced fetal weights, in both the ischemic horn and the nonischemic horn (P < .001). Antagonism of either endothelin receptor A or platelet-activating factor normalized fetal growth in both horns. Neither placental weight nor the incidence of fetal demise was affected by ischemia/reperfusion. Phospholipase A2-IIA and preproendothelin-1 messenger ribonucleic acid expression did not differ between right and left uterine horns in any group. Uterine and placental tissues in the ischemia/reperfusion group exhibited increased phospholipase A2-IIA (P < .01) but not preproendothelin-1.

CONCLUSION

Endothelin-1 and platelet-activating factor are both important mediators in the pathophysiology of ischemia/reperfusion-induced fetal growth restriction in the rat, contributing to the fetal growth restriction observed in both the ischemic and nonischemic horns. Antagonism of either mediator produces normal fetal growth in this model of fetal growth restriction.

Histomorphometric characterisation of shared and non-shared cotyledonary villus territories of monochorionic placentae in relation to pregnancy complications

OBJECTIVE

Theoretical estimates and physiological inferences suggest that the structure of a shared cotyledon differs from a non-shared cotyledon. The aim of this study was to characterise the histomorphometry of terminal villi in shared and non-shared cotyledons in monochorionic placentae, both from uncomplicated twins and from those with twin-twin transfusion syndrome (TTTS) or discordant growth restriction (DeltaIUGR).

METHODS

Forty-one monochorionic placentae from Caucasian non-smokers were obtained at caesarean section. Their vascular anatomy and placental territories were ascertained by dye injection. After fixation, full thickness histological blocks were obtained by systematic random sampling from each twin's territory and the shared cotyledons. Fifty randomly selected terminal villi were assessed for: (i) median villus diameter (ii) median villus capillary diameter (iii) median fetomaternal diffusion distance (iv) median no. of capillaries/villus (v) degree of vascularization (median percentage cross-sectional area of terminal villi occupied by capillaries) using a stage micrometer and image analysis programme. The histomorphometric findings were then correlated with birthweight discordance, placental territory discordance and DeltaAVAs (no. of AVAs from smaller twin (donor) to larger twin (recipient) minus no. of AVAs from larger to smaller twin).

RESULTS

Histomorphometric variables were similar in shared and non-shared cotyledons of uncomplicated MCDA twins. However, the median diameter of terminal villi in shared cotyledons in DeltaIUGR and TTTS placentae was significantly smaller [51.2 microm (48.2-58.3), p<0.001 and 52.6 microm (53.1-50.4), p<0.001], and had a similar number of smaller capillaries, larger fetomaternal diffusion distance and reduced vascularization compared to non-shared IUGR and TTTS placentae. However, Deltadiameter (defined as the difference between median diameters of terminal villi in large minus small twins' territories) rose with increasing birthweight discordance (Pearson correlation coefficient=0.82, p<0.001). Multiple linear regression analysis revealed that Deltadiameter was influenced by placental territory discordance (p<0.001) and birthweight discordance (p<0.01): log10 Deltadiameter=1.38+(0.01 x birthweight discordance)+(0.56 x log10 placental territory discordance) (R2=0.82, p<0.001), but there was no significant relationship with DeltaAVA and AAA. In the TTTS group, Deltadiameter correlated significantly with DeltaAVA only: log10Deltadiameter=1.44+(0.02 x DeltaAVA) (R2=0.3, p<0.001).

CONCLUSIONS

This is the first study to characterise the histomorphometry of shared and non-shared cotyledons in MC twins. The findings suggest that abnormal placentation, rather than placental vascular anatomy may be responsible for DeltaIUGR in MC twins, whereas TTTS arises from imbalance in interfetal transfusion with resultant differing terminal villus histomorphometric features in donor, recipient and shared cotyledons.

Perinatal outcome following amniotic septostomy in chronic TTTS is independent of placental angioarchitecture

OBJECTIVES

To determine whether the vascular anatomy of monochorial placenta influences the success of amniotic septostomy for the treatment of chronic mid-trimester twin-twin transfusion syndrome, we report placental anastomoses and perinatal data of 13 pregnancies treated by amniotic septostomy in combination with amnioreduction (AR). The placental anastomoses were delineated postnatally by perfusion studies. Perinatal outcome was also evaluated in relation to umbilical artery Doppler waveform of the donor twin.

RESULTS

The median gestational age at septostomy was 21 weeks (range 18 to 25.5 weeks). Amniotic septostomy in combination with single AR procedure successfully resolved polyhydramnios in all cases. The median gestational age at delivery and the septostomy to delivery interval were 27 weeks (range 20 to 34 weeks) and 4 weeks (range 0.3 to 13.6 weeks), respectively. Of the 26 fetuses, 10 died in utero and four died within a week of life, with a combined survival rate of 46%. There was no relation between the clinical outcome and angioarchitecture of the placenta. However, pregnancy loss was higher in the donor twin with absent end-diastolic flow umbilical artery Doppler waveform than those with end-diastolic flow (85 vs 17%; p < 0.001).

CONCLUSION

This study suggests that although amniotic septostomy is a promising method for the correction of oligohydramnios and/or polyhydramnios, perinatal survival rate does not depend on angioarchitecture of the placenta. Instead, umbilical artery Doppler waveform of the donor twin may be a better marker for survival rate.

Decreased vascularization and cell proliferation in placentas of intrauterine growth-restricted fetuses with abnormal umbilical artery flow velocity waveforms

OBJECTIVE

The purpose of this study was to compare the morphologic features of placentas in severe intrauterine fetal growth restriction with abnormal umbilical artery blood flow velocity waveforms and normal gestation.

STUDY DESIGN

Immunohistochemical methods were used to evaluate cell proliferation, vascular density, and alpha-smooth muscle actin expression by stromal cells in a group of 9 age-matched intrauterine growth-restricted and control placentas at 25 to 41 weeks of gestation.

RESULTS

Fewer MIB1-positive nuclei were observed in both trophoblast and stromal cell populations in intrauterine growth restriction, which indicates fewer cells in cycle. Furthermore, a greatly reduced vascular density was observed, along with higher levels of alpha-smooth muscle actin expression in stromal cells.

CONCLUSION

Intrauterine growth-restricted placentas show reduced cell proliferation in both trophoblast and stromal cell compartments. Peripheral villous vascularization is highly reduced.

Stereological quantification of placental villus vascularization and its relation to umbilical artery Doppler flow in intrauterine growth restriction

The aim of this study was to investigate the changes in the number of vessels within tertiary stem villi and intermediate/terminal villi which may be responsible for the abnormalities in placental vascular resistance and Doppler velocity index values in growth-restricted fetuses. The placentas of 20 cases with intrauterine growth restriction and 30 cases which were appropriate for gestational age were studied. The umbilical artery resistance index, pulsatility index and systolic to diastolic ratio were measured in each case. The vessels were quantified by a stereological method described previously and vascular surface density and the volume portion of the villi were calculated. The placentas of preterm and term cases with intrauterine growth restriction displayed significant reductions in the vascular surface density of stem and intermediate/terminal villi and volume portion of intermediate/terminal villi stroma when compared with gestation-matched normally grown cases (p<0.05). There was no significant correlation between Doppler index values of the umbilical artery and the stereological parameters of the intermediate/terminal and stem villi in the intrauterine growth restriction group (p>0.05). Some of the pregnancies with intrauterine growth restriction (six patients) with normal Doppler flow velocity waveforms had reduced vascularization in the placentas, and these pregnancies were found to have no perinatal complications. We conclude that,although the placental villi show reduced vascularization in pregnancies with intrauterine growth restriction, the Doppler indices may be normal and this normal flow pattern is related to reduced complication rate.

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.

Oxygen and placental vascular development

Human embryogenesis takes place in a hypoxic environment because the trophoblast shell excludes entry of maternal blood. The first fetal-placental villi develop as trophoblast sprouts. These are invaded by allantoic mesoderm to form secondary villi and are transformed, by vasculogenesis, into tertiary villi. The placental barrier to maternal blood is gradually breached between 8-12 weeks of gestation, due to invasion of placental-bed uteroplacental spiral arteries by the extravillous trophoblast (EVT). Placental oxygen tension thus rises and a phase of branching angiogenesis continues until 24 weeks. Thereafter a gradual shift takes place favoring non-branching angiogenesis. Gas-exchanging terminal villi thus form which are essential for rapid fetal growth and development of a high-flow, low-resistance fetal-placental circulation. Inadequate invasion of the uteroplacental spiral arteries by EVT results in placental ischemia and the development of obstetrical complications--preeclampsia and/or intrauterine growth restriction (IUGR). Placental villi often show evidence of continued branching angiogenesis, as is the case with anemic pregnancy, and pregnancy at high altitude. These structural alterations may reflect continued hypoxia-driven activity of vascular endothelial growth factor (VEGF). By contrast, a minority of severe early-onset IUGR pregnancies exhibit reduced fetal-placental blood flow with elongated maldeveloped villous capillaries. Placenta-like growth factor (PIGF) expression is increased while trophoblast proliferation is reduced, suggesting "hyperoxia" in the placental villous tree. IUGR may thus have two phenotypes--a more common hypoxic and a rarer hyperoxic type. While this concept is gaining acceptance, we have no insight as to the initiating mechanism(s).

Vascular Doppler techniques

Doppler ultrasound used for the assessment of the fetal umbilical circulation in the human pregnancy has been reported in the scientific literature since the early 1980s and has been rigorously evaluated by randomized, controlled trials. The consensus of the reviewers of these trials is that there do appear to be grounds for including umbilical artery Doppler ultrasound studies in the management of high-risk pregnancies. There is no apparent benefit for low-risk pregnancies or later gestation. Other fetal vascular beds are currently undergoing prospective studies and some limited randomized, controlled trials have been reported; but to date they are not at a point of development to be considered part of clinical management.