Venous drainage of the human uterus: respiratory gas studies in normal and fetal growth-retarded pregnancies

The effect of maternal position on placental blood flow and fetoplacental oxygenation in late gestation fetal growth restriction: a magnetic resonance imaging study

Fetal growth restriction (FGR) and maternal supine going-to-sleep position are both risk factors for late stillbirth. This study aimed to use magnetic resonance imaging (MRI) to quantify the effect of maternal supine position on maternal-placental and fetoplacental blood flow, placental oxygen transfer and fetal oxygenation in FGR and healthy pregnancies. Twelve women with FGR and 27 women with healthy pregnancies at 34-38 weeks' gestation underwent MRI in both left lateral and supine positions. Phase-contrast MRI and a functional MRI technique (DECIDE) were used to measure blood flow in the maternal internal iliac arteries (IIAs) and umbilical vein (UV), placental oxygen transfer (placental flux), fetal oxygen saturation (FO2 ), and fetal oxygen delivery (delivery flux). The presence of FGR, compared to healthy pregnancies, was associated with a 7.8% lower FO2 (P = 0.02), reduced placental flux, and reduced delivery flux. Maternal supine positioning caused a 3.8% reduction in FO2 (P = 0.001), and significant reductions in total IIA flow, placental flux, UV flow and delivery flux compared to maternal left lateral position. The effect of maternal supine position on fetal oxygen delivery was independent of FGR pregnancy, meaning that supine positioning has an additive effect of reducing fetal oxygenation further in women with FGR, compared to women with appropriately grown for age pregnancies. Meanwhile, the effect of maternal supine positioning on placental oxygen transfer was not independent of the effect of FGR. Therefore, growth-restricted fetuses, which are chronically hypoxaemic, experience a relatively greater decline in oxygen transfer when mothers lie supine in late gestation compared to appropriately growing fetuses. KEY POINTS: Fetal growth restriction (FGR) is the most common risk factor associated with stillbirth, and early recognition and timely delivery is vital to reduce this risk. Maternal supine going-to-sleep position is found to increase the risk of late stillbirth but when combined with having a FGR pregnancy, maternal supine position leads to 15 times greater odds of stillbirth compared to supine sleeping with appropriately grown for age (AGA) pregnancies. Using MRI, this study quantifies the chronic hypoxaemia experienced by growth-restricted fetuses due to 13.5% lower placental oxygen transfer and 26% lower fetal oxygen delivery compared to AGA fetuses. With maternal supine positioning, there is a 23% reduction in maternal-placental blood flow and a further 14% reduction in fetal oxygen delivery for both FGR and AGA pregnancies, but this effect is proportionally greater for growth-restricted fetuses. This knowledge emphasises the importance of avoiding supine positioning in late pregnancy, particularly for vulnerable FGR pregnancies.

Maternal Oxygen Administration during Labor: A Controversial Practice

Oxygen administration to the mother is commonly performed during labor, especially in the case of a non-reassuring fetal heart rate, aiming to increase oxygen diffusion through the placenta to fetal tissues. The benefits and potential risks are controversial, especially when the mother is not hypoxemic. Its impact on placental gas exchange and the fetal acid-base equilibrium is not fully understood and it probably affects the sensible placental oxygen equilibrium causing a time-dependent vasoconstriction of umbilical and placental vessels. Hyperoxia might also cause the generation of radical oxygen species, raising concerns for the developing fetal cells. Moreover, this practice affects the maternal cardiovascular system, causing alterations of the cardiac index, heart rate and vascular resistance, and unclear effects on uterine blood flow. In conclusion, there is no evidence that maternal oxygen administration can provide any benefit in the case of a non-reassuring fetal heart rate pattern, while possible collateral effects warn of its utilization. Oxygen administration during labor should be reserved for cases of maternal hypoxia.

Fetal oxygen and glucose utilization of uncomplicated monochorionic twins: Adapting to the intrauterine environment

INTRODUCTION

Monochorionic twins (MC) develop under unique intrauterine conditions and show a high risk of compromise during fetal life. Here we describe umbilical vein blood flow (UVBF) and fetal oxygen and glucose utilization in uncomplicated MC twins and investigate possible differences within twin-pairs according to birth-order.

METHODS

Prospective single-center study on 48 uncomplicated MC twins enrolled at the time of elective cesarean delivery. Ultrasound measurements of UVBF for Twin 1 and Twin 2 labelled according to birth-order were performed before spinal anesthesia. Umbilical arterial and venous blood samples were collected for each twin after fetal delivery, and fetal oxygen and glucose deliveries and uptakes were computed.

RESULTS

All twins were delivered within 2 min from one-another under steady-state conditions at 36.4 weeks of median gestational age (IQR 36.0-37.0). Birthweight and umbilical cord gas analyses were within physiological ranges for all twins. Second-born twins showed significantly lower UVBF, measured before delivery, and lower median birthweight compared to first-borns. Moreover, median values of estimated fetal oxygen and glucose consumption were lower in second compared to first MC twins.

DISCUSSION

Uncomplicated MC twins show different birthweight, oxygenation and metabolic rates based on their position in utero, hinting at pre-existing conditions possibly deriving by uneven vascular and metabolic distribution of the two placental territories. The innovative findings of this study emphasize the biological uniqueness of these pregnancies and prompt further physiological studies on MC twins and placenta metabolism.

Why is human uterine artery blood flow during pregnancy so high?

In healthy near-term women, blood flow to the uteroplacental circulation is estimated as 841 mL/min, which is greater than in other mammalian species. We argue that as uterine venous Po2 sets the upper limit for O2 diffusion to the fetus, high uterine artery blood flow serves to narrow the maternal arterial-to-uterine venous Po2 gradient and thereby raise uterine vein Po2. In support, we show that the reported levels for uterine artery blood flow agree with what is required to maintain normal fetal growth. Although residence at high altitudes (>2,500 m) depresses fetal growth, not all populations are equally affected; Tibetans and Andeans have higher levels of uterine artery blood flow than newcomers and exhibit normal fetal growth. Estimates of uterine venous Po2 from the umbilical blood-gas data available from healthy Andean pregnancies indicate that their high levels of uterine artery blood flow are consistent with their reported, normal birth weights. Unknown, however, are the effects on placental gas exchange of the lower levels of uterine artery blood flow seen in high-altitude newcomers or hypoxia-associated pregnancy complications. We speculate that, by widening the maternal artery to uterine vein Po2 gradient, lower levels of uterine artery blood flow prompt metabolic changes that slow fetal growth to match O2 supply.

An MRI approach to assess placental function in healthy humans and sheep

KEY POINTS

Human placental function is evaluated using non-invasive Doppler ultrasound of umbilical and uterine artery pulsatility indices as measures of resistance in placental vascular beds, while measurement of placental oxygen consumption ( V O 2 ) is only possible during Caesarean delivery. This study shows the feasibility of using magnetic resonance imaging (MRI) in utero to measure blood flow and oxygen content in uterine and umbilical vessels to calculate oxygen delivery to and V O 2 by the gravid uterus, uteroplacenta and fetus. Normal late gestational human uteroplacental V O 2 by MRI was ∼4 ml min^-1  kg^-1 fetal weight, which was similar to our MRI measurements in sheep and to those previously measured using invasive techniques. Our MRI approach can quantify uteroplacental V O 2 , which involves the quantification of maternal- and fetal-placental blood flows, fetal oxygen delivery and V O 2 , and the oxygen gradient between uterine- and umbilical-venous blood, providing a comprehensive assessment of placental function with clinical potential.

ABSTRACT

It has not been feasible to perform routine clinical measurement of human placental oxygen consumption ( V O 2 ) and in vitro studies do not reflect true metabolism in utero. Here we propose an MRI method to non-invasively quantify in utero placental and fetal oxygen delivery ( D O 2 ) and V O 2 in healthy humans and sheep. Women (n = 20) and Merino sheep (n = 10; 23 sets of measurements) with singleton pregnancies underwent an MRI in late gestation (36 ± 2 weeks and 128 ± 9 days, respectively; mean ± SD). Blood flow (phase-contrast) and oxygen content (T1 and T2 relaxometry) were measured in the major uterine- and umbilical-placental vessels, allowing calculation of uteroplacental and fetal D O 2 and V O 2 . Maternal D O 2 (ml min^-1  kg^-1 fetus) to the gravid uterus was similar in humans and sheep (human = 54 ± 15, sheep = 53 ± 21, P = 0.854), while fetal D O 2 (human = 25 ± 4, sheep = 22 ± 5, P = 0.049) was slightly lower in sheep. Uteroplacental and fetal V O 2 (ml min^-1  kg^-1 fetus; uteroplacental: human = 4.1 ± 1.5, sheep = 3.5 ± 1.9, P = 0.281; fetus: human = 6.8 ± 1.3, sheep = 7.2 ± 1.7, P = 0.426) were similar between species. Late gestational uteroplacental:fetal V O 2 ratio did not change with age (human, P = 0.256; sheep, P = 0.121). Human umbilical blood flow (ml min^-1  kg^-1 fetus) decreased with advancing age (P = 0.008), while fetal V O 2 was preserved through an increase in oxygen extraction (P = 0.046). By contrast, sheep fetal V O 2 was preserved through stable umbilical flow (ml min^-1  kg^-1 ; P = 0.443) and oxygen extraction (P = 0.582). MRI derived measurements of uteroplacental and fetal V O 2 between humans and sheep were similar and in keeping with prior data obtained using invasive techniques. Taken together, these data confirm the reliability of our approach, which offers a novel clinical 'placental function test'.

Hemodynamic Complications in Pregnancy: Preeclampsia and Beyond

Normal pregnancy is a complex and dynamic process that requires significant adaptation from the maternal system. Failure of this adaptive process in pregnancy contributes to many pregnancy related disorders, including the hypertensive disorders of pregnancy. This article discusses placental development and how abnormalities in the process of vascular remodeling contribute to the multisystem maternal and fetal disease that is preeclampsia and fetal growth restriction. We review some of the consequences of this condition on the mother and fetus, aspects of the clinical management of preeclampsia and how it can influence both mother and infant in the postnatal period and beyond.

Fetal Oxygen and Glucose Consumption in Human Pregnancy Complicated by Fetal Growth Restriction

In healthy pregnancy, glucose and oxygen availability are essential for fetal growth and well being. However, how substrate delivery and fetal uptake are affected in human pregnancy complicated by fetal growth restriction (FGR) is still unknown. Here, we show that the human FGR fetus has a strikingly reduced umbilical uptake of both oxygen and glucose. In 30 healthy term and 32 FGR human pregnancies, umbilical volume flow (Qumb) and parallel umbilical vein (uv) and artery (ua) blood samples were obtained at elective Cesarean section to calculate fetal glucose and oxygen uptake as Qumb · Δ (uv-ua) differences. Umbilical blood flow was significantly lower in FGR pregnancy (-63%; P<0.001) but not when normalized for fetal body weight. FGR pregnancy had significantly lower umbilical oxygen delivery and uptake, both as absolute values (delivery: -78%; uptake: -78%) and normalized (delivery: -50%; uptake: -48%) for fetal body weight (all P<0.001). Umbilical glucose absolute delivery and uptake were significantly reduced (delivery: -68%; uptake: -72%) but only glucose uptake was decreased when normalized for fetal body weight (-30%; P<0.05). The glucose/oxygen quotient was significantly increased (+100%; P<0.05) while glucose clearance was significantly decreased (71%; P<0.001) in FGR pregnancy (both P<0.05). The human fetus in FGR pregnancy triggers compensatory mechanisms to reduce its metabolic rate, matching the proportion of substrate consumption relative to oxygen delivery as a survival strategy during complicated pregnancy.

Minimally invasive radical hysterectomy: an analysis of oncologic outcomes from Hospital Italiano (Argentina)

BACKGROUND

The Laparoscopic Approach to Cervical Cancer (LACC) trial demonstrated a higher rate of disease recurrence and worse disease-free survival in patients who underwent minimally invasive radical hysterectomy.

OBJECTIVES

To evaluate surgical and oncological outcome of laparoscopic radical hysterectomy performed at Hospital Italiano in Buenos Aires, Argentina.

METHODS

This retrospective study included all patients with cervical cancer, 2009 FIGO stage IA1, with lymphovascular invasion to IB1 (<4 cm) who underwent a laparoscopic radical hysterectomy between June 2010 and June 2015. Patients were eligible if they had squamous cell carcinoma, adenocarcinoma, or adenosquamous carcinoma, and no lymph node involvement by imaging. Patients must have undergone a type C1 radical hysterectomy. Only patients who were treated by a laparoscopic approach were included. Patients were excluded if histopathology showed a component of neuroendocrine carcinoma before or after surgery; if they had synchronous primary tumors, history of abdominal or pelvic radiotherapy, or were operated on at an outside institution; and if they had only surgery and no follow-up in our institution. Relapse rate and disease-free survival were evaluated using the Kaplan-Meier method.

RESULTS

A total of 108 patients were evaluated. The median age was 41 years (range 27-70). Distribution of histologic sub-types was squamous carcinoma in 77 patients (71%), adenocarcinoma in 27 patients (25%), and adenosquamous carcinoma in four patients (4%). Ninety-nine patients (92%) had stage IB1 tumors and 58 (54%) patients had tumors ≤2 cm. The median surgical time was 240 min (range 190-290), the median estimated blood loss was 140 mL (range 50-500) and the transfusion rate was 3.7%. The median length of hospital stay was 2 days (range 1-11). The median follow-up time was 39 months (range 11-83). The global recurrence rate after laparoscopic radical hysterectomy was 15% (16/108). According to tumor size, the recurrence rate was 12% in patients with tumors ≤2 cm (7/58) and 18% in patients with tumors >2 cm (9/50) (OR=0.76; 95% CI 0.26 to 2.22; p=0.62) The 3- and 5-year relapse rate was 17% (95% CI 11% to 27%). The 3- and 5-year disease-free survival was 81% (95% CI 71% to 88%) and 70% (95% CI 43% to 86%), respectively. Overall survival at 3 years was 87% (95% CI 76% to 93%).

CONCLUSION

The recurrence rate after laparoscopic radical hysterectomy was 15%, and in tumors ≤2 cm it was 12%. The 3-year disease-free survival was 81%. Given these results our hospital has changed the approach to open radical hysterectomy.

Uterine and fetal placental Doppler indices are associated with maternal cardiovascular function

BACKGROUND

The mechanism underlying fetal-placental Doppler index changes in preeclampsia and/or fetal growth restriction are unknown, although both are associated with maternal cardiovascular dysfunction.

OBJECTIVE

We sought to investigate whether there was a relationship between maternal cardiac output and vascular resistance and fetoplacental Doppler findings in healthy and complicated pregnancy.

STUDY DESIGN

Women with healthy pregnancies (n=62), preeclamptic pregnancies (n=13), preeclamptic pregnancies with fetal growth restriction (n=15), or fetal growth restricted pregnancies (n=17) from 24-40 weeks gestation were included. All of them underwent measurement of cardiac output with the use of an inert gas rebreathing technique and derivation of peripheral vascular resistance. Uterine and fetal Doppler indices were recorded; the latter were z scored to account for gestation. Associations were determined by polynomial regression analyses.

RESULTS

Mean uterine artery pulsatility index was higher in fetal growth restriction (1.37; P=.026) and preeclampsia+fetal growth restriction (1.63; P=.001) but not preeclampsia (0.92; P=1) compared with control subjects (0.8). There was a negative relationship between uterine pulsatility index and cardiac output (r²=0.101; P=.025) and umbilical pulsatility index z score and cardiac output (r²=0.078; P=.0015), and there were positive associations between uterine pulsatility index and peripheral vascular resistance (r²=0.150; P=.003) and umbilical pulsatility index z score and peripheral vascular resistance (r²= 0.145; P=.001). There was no significant relationship between cardiac output and peripheral vascular resistance with cerebral Doppler indices.

CONCLUSION

Uterine artery Doppler change is abnormally elevated in fetal growth restriction with and without preeclampsia, but not in preeclampsia, which may explain the limited sensitivity of uterine artery Doppler changes for all these complications when considered in aggregate. Furthermore, impedance within fetoplacental arterial vessels is at least, in part, associated with maternal cardiovascular function. This relationship may have important implications for fetal surveillance and would inform therapeutic options in those pathologic pregnancy conditions currently, and perhaps erroneously, attributed purely to placental maldevelopment. Uterine and fetal placental Doppler indices are associated significantly with maternal cardiovascular function. The classic description of uterine and fetal Doppler changes being initiated by placental maldevelopment is a less plausible explanation for the pathogenesis of the conditions than that relating to maternal cardiovascular changes.

Matrix Metalloproteinase Release From Placental Explants of Pregnancies Complicated by Intrauterine Growth Restriction

OBJECTIVE

There is evidence of impaired placental development in intrauterine growth restriction (IUGR). Matrix metalloproteinases (MMPs) are extracellular matrix-degrading enzymes that are released by placental cells during tissue remodeling processes. We hypothesized 1) that release of MMP-2 and -9 is decreased and/or release of tissue inhibitors of metalloproteinases (TIMPs) is increased from placental explants in pregnancies complicated by IUGR and 2) that oxygen levels affect such release.

METHODS

Placental villous explants from normal (n = 7) and IUGR (n = 7) pregnancies were cultured at high (20%) and low (3%) oxygen levels for 24 hours. Supernatants were analyzed for MMP-2 and MMP-9 by zymography and for TIMP-1 and -2 by western blot analysis.

RESULTS

: At 20% oxygen there was significantly reduced MMP-2 (P < .05) and TIMP-1 (P < .01) release and a trend for decreased MMP-9 release (P = .07) in explants from IUGR pregnancies compared with normal pregnancies; however, there were no differences at 3% oxygen. TIMP-2 was below detectable levels in all samples. Although MMP-2 and TIMP-1 release was significantly reduced at 3% compared with 20% oxygen in explants from both normal (P < .001; P < .05) and IUGR (P < .05) pregnancies, MMP-2 release changed less in IUGR compared with normal explant cultures. There were no significant effects of oxygen on MMP-9 release.

CONCLUSION

Placental explants from IUGR pregnancies demonstrated reduced MMP-2, MMP-9, and TIMP-1 release compared with explants from normal pregnancies at high (20%) but not low (3%) oxygen.

Impaired Angiogenic Potential of Human Placental Mesenchymal Stromal Cells in Intrauterine Growth Restriction

Human placental mesenchymal stromal cells (pMSCs) have never been investigated in intrauterine growth restriction (IUGR). We characterized cells isolated from placental membranes and the basal disc of six IUGR and five physiological placentas. Cell viability and proliferation were assessed every 7 days during a 6-week culture. Expression of hematopoietic, stem, endothelial, and mesenchymal markers was evaluated by flow cytometry. We characterized the multipotency of pMSCs and the expression of genes involved in mitochondrial content and function. Cell viability was high in all samples, and proliferation rate was lower in IUGR compared with control cells. All samples presented a starting heterogeneous population, shifting during culture toward homogeneity for mesenchymal markers and occurring earlier in IUGR than in controls. In vitro multipotency of IUGR-derived pMSCs was restricted because their capacity for adipocyte differentiation was increased, whereas their ability to differentiate toward endothelial cell lineage was decreased. Mitochondrial content and function were higher in IUGR pMSCs than controls, possibly indicating a shift from anaerobic to aerobic metabolism, with the loss of the metabolic characteristics that are typical of undifferentiated multipotent cells.

SIGNIFICANCE

This study demonstrates that the loss of endothelial differentiation potential and the increase of adipogenic ability are likely to play a significant role in the vicious cycle of abnormal placental development in intrauterine growth restriction (IUGR). This is the first observation of a potential role for placental mesenchymal stromal cells in intrauterine growth restriction, thus leading to new perspectives for the treatment of IUGR.

Placental oxygen transport estimated by the hyperoxic placental BOLD MRI response

Estimating placental oxygen transport capacity is highly desirable, as impaired placental function is associated with fetal growth restriction (FGR) and poor neonatal outcome. In clinical obstetrics, a noninvasive method to estimate the placental oxygen transport is not available, and the current methods focus on fetal well-being rather than on direct assessment of placental function. In this article, we aim to estimate the placental oxygen transport using the hyperoxic placental blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) response. In 21 normal pregnancies and in four cases of severe early onset FGR, placental BOLD MRI was performed in a 1.5 Tesla MRI system (TR:8000 msec, TE:50 msec, Flip angle:90). Placental histological examination was performed in the FGR cases. In normal pregnancies, the average hyperoxic placental BOLD response was 12.6 ± 5.4% (mean ± SD). In the FGR cases, the hyperoxic BOLD response was abnormal only in cases with histological signs of maternal hypoperfusion of the placenta. The hyperoxic placental BOLD response is mainly derived from an increase in the saturation of maternal venous blood. In the normal placenta, the pO₂ of the umbilical vein is closely related to the pO₂ of the uterine vein. Therefore, the hyperoxic placental BOLD response may reflect the placental oxygen supply to the fetus. In early onset FGR, the placental oxygen transport is reduced mainly because of the maternal hypoperfusion, and in these cases the placental BOLD response might be altered. Thus, the placental BOLD MRI might provide direct noninvasive assessment of placental oxygen transport.

UNDERSTANDING THE PLACENTAL AETIOLOGY OF FETAL GROWTH RESTRICTION; COULD THIS LEAD TO PERSONALIZED MANAGEMENT STRATEGIES?

Fetal growth restriction (FGR) is defined as the failure of a fetus to attain its full genetic growth potential. It is a leading cause of stillbirth, prematurity, cerebral palsy and perinatal mortality. Small size at birth increases surviving infants’ lifelong risk of adverse health outcomes associated with the metabolic syndrome. The pathophysiology of abnormal fetal growth is extremely complex and incompletely understood, with a plethora of genetic, signalling and metabolic candidates under investigation, many of which may result in abnormal structure and function of the placenta. In contrast to, or maybe because of, the underlying complexities of FGR, the strategies clinicians have for identifying and managing this outcome are conspicuously limited. Current clinical practice is restricted to identifying pregnancies at risk of FGR, and when FGR is detected, using intensive monitoring to guide the timing of delivery to optimise fetal outcomes. Abnormal Doppler indices in the umbilical artery are strongly associated with poor perinatal outcomes and are currently the “gold standard” for clinical surveillance of the growth-restricted fetus.

Elevated plasma norepinephrine inhibits insulin secretion, but adrenergic blockade reveals enhanced β-cell responsiveness in an ovine model of placental insufficiency at 0.7 of gestation

In pregnancies complicated by placental insufficiency (PI), fetal hypoglycemia and hypoxemia progressively worsen during the third trimester, which increases circulating norepinephrine (NE). Pharmacological adrenergic blockade (ADR-block) at 0.9 gestation revealed that NE inhibits insulin secretion and enhanced β-cell responsiveness in fetuses with PI-induced intrauterine growth restriction (IUGR). NE concentrations in PI fetuses at 0.7 gestation were threefold greater compared with age-matched controls, but the levels were similar to near-term controls. Therefore, our objective was to determine whether elevations in plasma NE concentrations inhibit insulin secretion and produce compensatory β-cell responsiveness in PI fetuses at 0.7 gestation. Fetal insulin was measured under basal, glucose-stimulated insulin secretion (GSIS) and glucose-potentiated arginine-stimulated insulin secretion (GPAIS) conditions in the absence and presence of an ADR-block. Placental weights were 38% lower (P < 0.05) in PI fetus than in controls, but fetal weights were not different. PI fetuses had lower (P < 0.05) basal blood oxygen content, plasma glucose, insulin-like growth factor-1 and insulin concentrations and greater plasma NE concentrations (891 ± 211 v. 292 ± 65 pg/ml; P < 0.05) than controls. GSIS was lower in PI fetuses than in controls (0.34 ± 0.03 v. 1.08 ± 0.06 ng/ml; P < 0.05). ADR-block increased GSIS in PI fetuses (1.19 ± 0.11 ng/ml; P < 0.05) but decreased GSIS in controls (0.86 ± 0.02 ng/ml; P < 0.05). Similarly, GPAIS was 44% lower (P < 0.05) in PI fetuses than in controls, and ADR-block increased (P < 0.05) GPAIS in PI fetuses but not in controls. Insulin content per islet was not different between treatments. We conclude that elevations in fetal plasma NE suppress insulin concentrations, and that compensatory β-cell stimulus-secretion responsiveness is present before IUGR.

Placental mitochondrial content and function in intrauterine growth restriction and preeclampsia

Intrauterine growth restriction (IUGR) and pregnancy hypertensive disorders such as preeclampsia (PE) associated with IUGR share a common placental phenotype called "placental insufficiency", originating in early gestation when high availability of energy is required. Here, we assess mitochondrial content and the expression and activity of respiratory chain complexes (RCC) in placental cells of these pathologies. We measured mitochondrial (mt)DNA and nuclear respiratory factor 1 (NRF1) expression in placental tissue and cytotrophoblast cells, gene and protein expressions of RCC (real-time PCR and Western blotting) and their oxygen consumption, using the innovative technique of high-resolution respirometry. We analyzed eight IUGR, six PE, and eight uncomplicated human pregnancies delivered by elective cesarean section. We found lower mRNA levels of complex II, III, and IV in IUGR cytotrophoblast cells but no differences at the protein level, suggesting a posttranscriptional compensatory regulation. mtDNA was increased in IUGR placentas. Both mtDNA and NRF1 expression were instead significantly lower in their isolated cytotrophoblast cells. Finally, cytotrophoblast RCC activity was significantly increased in placentas of IUGR fetuses. No significant differences were found in PE placentas. This study provides genuine new data into the complex physiology of placental oxygenation in IUGR fetuses. The higher mitochondrial content in IUGR placental tissue is reversed in cytotrophoblast cells, which instead present higher mitochondrial functionality. This suggests different mitochondrial content and activity depending on the placental cell lineage. Increased placental oxygen consumption might represent a limiting step in fetal growth restriction, preventing adequate oxygen delivery to the fetus.

Umbilical uptakes and transplacental concentration ratios of amino acids in severe fetal growth restriction

BACKGROUND

This study examines the relationship between placental amino acid (AA) transport and fetal AA demand in an ovine fetal growth restriction (FGR) model in which placental underdevelopment induces fetal hypoxemia and hypoglycemia.

METHODS

Umbilical uptakes of AA, oxygen, glucose, and lactate were measured near term in eight experimental ewes (FGR group) and in eight controls (C group).

RESULTS

The FGR group demonstrated significantly reduced umbilical uptakes of oxygen, glucose, lactate, and 11 AAs per kg fetus. The combined uptake of glucose, lactate, and AAs, expressed as nutrient/oxygen quotients, was reduced almost to 1.00 (FGR: 1.05 vs. C: 1.32, P ≤ 0.02). In contrast to a decrease in umbilical glucose concentration, all but one of the AAs that were transported from placenta to fetus demonstrated normal or elevated fetal concentrations, and five of the essential AAs were transported against a significantly higher feto/maternal (F/M) concentration ratio. This ratio peaked at the lowest fetal oxygen levels.

CONCLUSION

We conclude that, in the hypoxic FGR fetus, the reduction in AA uptake is not due to a disproportionally small placental AA transport capacity. It is the consequence of decreased fetal oxidative metabolism and growth rate, which together reduce fetal AA demand.

The timing and duration of hypoxia determine gene expression patterns in cultured human trophoblasts

OBJECTIVE

Exposure of cultured trophoblasts to hypoxia is commonly used to interrogate the molecular mechanisms underlying placental hypoxic injury. We examined the effect of levels, durations, and patterns of hypoxia on gene expression patterns in primary human trophoblasts.

STUDY DESIGN

We exposed primary term human trophoblasts to either standard culture conditions (O(2) = 20%) or to static or alternating levels of oxygen (O(2) = 8%, or O(2) = 0%) either early or late in culture, and analyzed the expression of 34 genes that are known to be regulated in placentas from pregnancies complicated by fetal growth restriction (FGR).

RESULTS

Using multidimensional scale analysis, Euclidean distance, and hierarchical clustering, we found that gene expression patterns in cells exposed to O(2) = 8% were similar to patterns observed in O(2) = 20%, but more distant from patterns in O(2) = 0%. Alternating atmospheric oxygen (8% vs. 0%) yielded intermediate results. Changes in oxygen levels over a longer period had a greater effect on gene expression than short-term changes. Gene expression patterns in cultured trophoblasts did not fully capture expression patterns observed in biopsies from FGR placentas vs. control.

CONCLUSIONS

The level, duration, and patterns of hypoxia are critical in determining trophoblast gene expression, and therefore germane for analysis of trophoblast hypoxic injury.

Fetal oxygenation and maternal ventilation

In the past 20 years, measurements of umbilical blood flow and umbilical venous PO2, oxygen saturation, pH, and oxygen capacity have provided reliable information about the state of oxygenation of normal and growth restricted human fetuses. However, no comparable information is available about the uterine circulation. Therefore, understanding of oxygen transport across the human placenta and the effect of maternal ventilation on fetal oxygenation is tentative, and currently based on a model that is derived from evidence in another species. The main purpose of this model is to illustrate the kind of information that is needed to make further progress in this area.

Placental size and the prediction of severe early-onset intrauterine growth restriction in women with low pregnancy-associated plasma protein-A

OBJECTIVES

Screening studies for trisomy 21 demonstrate that low maternal serum pregnancy-associated plasma protein-A (PAPP-A) at 11-13 weeks' gestation is associated with stillbirth, intrauterine growth restriction (IUGR) and pre-eclampsia in chromosomally normal fetuses. However, the strength of these associations is too weak to justify screening for these placental insufficiency syndromes. Our objective was to evaluate placental size and uterine artery (UtA) Doppler imaging as second-stage screening tests for women with low PAPP-A.

METHODS

We prospectively studied 90 normal singleton pregnancies with first-trimester PAPP-A </= 0.30 multiples of the median. Maternal serum alpha-fetoprotein (AFP) at 15-18 weeks' gestation, and second-trimester placental size and UtA Doppler indices were assessed as predictors of pregnancy outcome.

RESULTS

The risks of IUGR, preterm delivery before 32 weeks' gestation and stillbirth were significantly associated with small placental size (relative risk (RR), 3.96; 95% CI, 2.21-5.98; RR, 3.96; 95% CI, 2.21-5.98; and RR, 6.44, 95% CI, 2.74-14.54, respectively) and elevated AFP (RR, 3.67; 95% CI, 1.78-7.71; RR, 2.48; 95% CI, 1.23-4.94; and RR, 5.14; 95% CI, 1.66-16.85, respectively), but not with abnormal UtA Doppler indices. The combination of elevated AFP and small placental size further increased the risk of IUGR (RR, 4.88; 95% CI, 2.88-5.31), delivery before 32 weeks' gestation (RR, 4.25; 95% CI, 2.38-4.98) and stillbirth (RR, 7.44; 95% CI, 3.04-3.75).

CONCLUSIONS

Small placental size and elevated AFP, but not UtA Doppler indices, identify women with low PAPP-A at high risk of IUGR, extreme preterm delivery and stillbirth. These additional screening tests may directly improve perinatal outcomes in women with low PAPP-A.

Rheological and physiological consequences of conversion of the maternal spiral arteries for uteroplacental blood flow during human pregnancy

Physiological conversion of the maternal spiral arteries is key to a successful human pregnancy. It involves loss of smooth muscle and the elastic lamina from the vessel wall as far as the inner third of the myometrium, and is associated with a 5–10-fold dilation at the vessel mouth. Failure of conversion accompanies common complications of pregnancy, such as early-onset preeclampsia and fetal growth restriction. Here, we model the effects of terminal dilation on inflow of blood into the placental intervillous space at term, using dimensions in the literature derived from three-dimensional reconstructions. We observe that dilation slows the rate of flow from 2 to 3 m/s in the non-dilated part of an artery of 0.4–0.5 mm diameter to approximately 10 cm/s at the 2.5 mm diameter mouth, depending on the exact radius and viscosity. This rate predicts a transit time through the intervillous space of approximately 25 s, which matches observed times closely. The model shows that in the absence of conversion blood will enter the intervillous space as a turbulent jet at rates of 1–2 m/s. We speculate that the high momentum will damage villous architecture, rupturing anchoring villi and creating echogenic cystic lesions as evidenced by ultrasound. The retention of smooth muscle will also increase the risk of spontaneous vasoconstriction and ischaemia–reperfusion injury, generating oxidative stress. Dilation has a surprisingly modest impact on total blood flow, and so we suggest the placental pathology associated with deficient conversion is dominated by rheological consequences rather than chronic hypoxia.

An animal model of placental insufficiency-induced intrauterine growth restriction

Intrauterine growth restriction (IUGR), often associated with functional placental insufficiency, results in increased perinatal mortality and morbidity. For obvious reasons, many questions regarding the progression of IUGR pregnancies cannot be addressed experimentally in humans, predicating the use of animal models. Although no animal model fully recapitulates human pregnancy, the pregnant sheep has been used extensively to investigate maternal-fetal interactions. In sheep, surgical placement of catheters in both the maternal and fetal vasculature allows repeated sampling from nonanesthetized pregnancies. Considerable insight has been gained on placental oxygen and nutrient transfer and utilization from use of pregnant sheep, often confirmed in the human once appropriate technologies became available. This review will focus on one sheep model, used to examine the impact of placental insufficiency-induced IUGR on oxygen and nutrient transport and utilization.

Bax, Bak and mitochondrial oxidants are involved in hypoxia-reoxygenation-induced apoptosis in human placenta

Although apoptosis is prominent in placental cells in pregnancy complications such as preeclampsia, the cause is unknown. We surmised that hypoxia-reoxygenation (HR) is the mechanism and hypothesized that mitochondrial oxidants and Bcl-2 proteins cause HR-induced placental apoptosis. Our goal was studying expression of five Bcl-2 proteins--Bcl-2, Bcl-xL, Bax, Bak, Bad--and testing effects of diazoxide and cyclosporine A on oxidative stress and apoptosis in villous tissues subjected to HR. Term human placentas were obtained from normal pregnancies following elective caesarean deliveries. Villous tissues were subjected to "repetitive HR" (one hour at 2% O(2) then one hour at 8% O(2), alternatively, for a total of 6h) or "prolonged HR" (3h at 2% O(2) then 3h of 8% O(2)). Samples maintained at 2% and 8% O(2) served as hypoxic and normoxic controls, respectively. Prolonged HR caused the most severe villous apoptotic changes, increased the expression of Bax and Bak mRNA and protein and reduced the expression of Bcl-2 mRNA. Pre-administration of diazoxide and cyclosporine A reduced TUNEL-positive nuclei and levels of nitrotyrosine and 4-hydroxy-2-nonenol after prolonged HR. Thus, duration of hypoxia and reoxygenation is important in determining severity of HR-induced apoptosis in placenta. These apoptotic changes are closely associated with Bax and Bak effects and oxidative stress in mitochondria.

The maternal plasma soluble vascular endothelial growth factor receptor-1 concentration is elevated in SGA and the magnitude of the increase relates to Doppler abnormalities in the maternal and fetal circulation

OBJECTIVES

The soluble form of vascular endothelial growth factor receptor-1 (sVEGFR-1), an antagonist to vascular endothelial growth factor and placental growth factor, has been implicated in the pathophysiology of preeclampsia. Preeclampsia and pregnancy complicated with small for gestational age (SGA) fetuses share some pathophysiologic derangements, such as failure of physiologic transformation of the spiral arteries, endothelial cell dysfunction, and leukocyte activation. The objectives of this study were to: (1) determine whether plasma concentrations of sVEGFR-1 in mothers with SGA fetuses without preeclampsia at the time of diagnosis are different from those in patients with preeclampsia or normal pregnant women, and (2) examine the relationship between plasma concentrations of sVEGFR-1 and Doppler velocimetry in uterine and umbilical arteries in patients with preeclampsia and those with SGA.

STUDY DESIGN

A cross-sectional study was conducted to determine the concentrations of the soluble form of VEGFR-1 in plasma obtained from normal pregnant women (n = 135), women with SGA fetuses (n = 53), and patients with preeclampsia (n = 112). Patients with SGA fetuses and those with preeclampsia were sub-classified according to the results of uterine and umbilical artery Doppler velocimetry examinations. Plasma concentrations of sVEGFR-1 were determined by an ELISA. Since these concentrations change with gestational age, differences among various subgroups were statistically estimated with the delta value, defined as the difference between the observed and expected plasma sVEGFR-1 concentration. The expected values were derived from regression analysis of plasma sVEGFR-1 concentrations in normal pregnancy. Regression analysis and univariate and multivariate analysis were employed.

RESULTS

(1) Mothers with SGA fetuses had a mean plasma concentration of sVEGFR-1 higher than normal pregnant women (p < 0.001), but lower than patients with preeclampsia (p < 0.001). (2) Among patients with SGA fetuses, only those with abnormal uterine artery Doppler velocimetry had a mean plasma sVEGFR-1 concentration significantly higher than normal pregnant women (p < 0.001). (3) Among mothers with SGA fetuses in whom Doppler velocimetry was performed (n = 41), those with abnormalities in both the uterine and umbilical artery velocimetry had the highest mean delta of sVEGFR-1 plasma concentration (mean +/- standard deviation (SD): 0.69 +/- 0.29). Conversely, patients who had normal Doppler velocimetry in both uterine and umbilical arteries had the lowest mean delta (mean +/- SD: 0.09 +/- 0.29) of sVEGFR-1 plasma concentrations (ANOVA; p < 0.001). (4) Among patients with preeclampsia in whom Doppler velocimetry was performed (n = 69), those with abnormalities in both the uterine and umbilical artery velocimetry had the highest mean delta sVEGFR-1 plasma concentration (mean +/- SD: 1.01 +/- 0.22) among all groups classified (ANOVA; p < 0.001). (5) Among patients with SGA and those with preeclampsia, there was a relationship (Chi-square for trend p < 0.001 for both) between the severity of Doppler velocimetry abnormalities and the proportion of patients who had high delta sVEGFR-1 plasma concentrations (defined as a concentration two standard deviations (2SD) above the mean delta of normal pregnant women). (6) Multiple regression analysis suggested that the diagnostic category (e.g., SGA or preeclampsia), Doppler abnormalities, and gestational age at blood sampling were associated with an increase in plasma sVEGFR-1 concentrations (p < 0.001).

CONCLUSIONS

These observations provide support for the participation of the soluble receptor of vascular endothelial growth factor in the pathophysiology of SGA with abnormal uterine artery Doppler velocimetry and preeclampsia. An excess of sVEGFR-1 is released into the maternal circulation of patients with preeclampsia and those with SGA fetuses, as abnormalities of impedance to blood flow involve uterine and umbilical circulation.

Determinants of adverse perinatal outcome in high-risk women with abnormal uterine artery Doppler images

OBJECTIVE

The purpose of this study was to evaluate the prognostic role of placental ultrasound imaging at 19-23 weeks of gestation in clinically high-risk women with abnormal uterine artery Doppler (UTAD).

STUDY DESIGN

Placentas of 60 women with abnormal UTAD were examined at 19-23 weeks of gestation for shape and texture abnormalities. Findings were correlated with clinical outcomes (preterm delivery at <32 weeks of gestation; birth weight <10th percentile [small for gestational age]; preeclampsia/hemolysis, elevated liver enzymes, low platelets; early-onset intrauterine growth restriction with abnormal umbilical artery Doppler; and intrauterine fetal death) and maternal serum screening data. Placental disease was reviewed by 2 perinatal pathologists.

RESULTS

Women with abnormal placental shape at 19-23 weeks of gestation (n = 28) had higher odds of intrauterine fetal death (odds ratio, 4.5; 95% CI, 1.3-15.6), delivery at <32 weeks of gestation (odds ratio, 4.7; 95% CI, 1.6-14.1]), and intrauterine growth restriction (odds ratio, 4.7; 95% CI, 1.4-15.1]) than did the women with a normal placental shape. Thirty-two of 41 placentas (74%) weighed <10th percentile, and 36 of 43 placentas (83%) had ischemic-thrombotic pathologic condition. There was no association between abnormal placental shape at 19-23 weeks of gestation and placental weight, but 5 of 6 placentas that were <10 cm long were <10th percentile for weight at delivery. There was a poor correlation between measures of ultrasound texture at 19-23 weeks of gestation and the presence of specific lesions at delivery.

CONCLUSION

Combined abnormal UTAD and placental dysmorphologic condition before fetal viability identifies a subset of women who are at risk of adverse outcomes. Placental size is critical in the determination of the outcome in this situation because of the very high prevalence of destructive lesions, although present methods of placental imaging have significant limitations.

Placental expression of soluble fms-like tyrosine kinase 1 is increased in singletons and twin pregnancies with intrauterine growth restriction

OBJECTIVE

Intrauterine growth restriction (IUGR) is characterized by decreased placental perfusion. Low oxygen has been shown to increase soluble fms-like tyrosine kinase 1 (sFlt-1) expression in the human placenta. The objective of this study was to examine sFlt-1 expression in different types of IUGR pregnancies, including early-onset severe cases characterized by abnormal umbilical and uterine artery Doppler and discordant IUGR twins in which the normal cotwin represents the optimal control because both placentas share the same uterine environment.

PATIENTS

Placentas from four subgroups were collected: early severe IUGR with umbilical artery absent end diastolic flow (n = 19), small for gestational age with normal uterine and umbilical artery Doppler (n = 11), severely growth-restricted dichorionic and monochorionic twins with abnormal umbilical artery Doppler (n = 9), preeclamptic twins (n = 3), and age-matched normal singletons (n = 19) and twin controls (n = 8).

RESULTS

Expression of sFlt-1 mRNA and protein was significantly increased in IUGR placentas compared with small for gestational age and normal control placentas. sFlt-1 expression levels were also significantly greater in the small IUGR twin placentas from discordant twin pregnancies compared with the normal cotwin. In preeclamptic twins, sFlt-1 expression was increased in only one of the two placentas.

CONCLUSIONS

Our results demonstrate that sFlt-1 expression is increased in severe IUGR placentas with abnormal umbilical artery Doppler of singletons and also in discordant IUGR twins. Reduced placental perfusion may contribute to the increased expression of sFlt-1 in IUGR pregnancies. Our data are compatible with differential sFlt-1 expression in placentas from discordant twins.

Severe intrauterine growth restriction pregnancies have increased placental endoglin levels: hypoxic regulation via transforming growth factor-beta 3

Endoglin, a co-receptor for transforming growth factor (TGF)-beta 1 and -beta 3 is expressed in the human placenta and plays an important role in the pathogenesis of preeclampsia. Because preeclampsia is associated with hypoxia, and because TGF-beta 3 is overexpressed in preeclamptic pregnancies, we examined the effect of oxygen and TGF-beta 3 on placental endoglin expression and investigated its expression in pathological models of placental hypoxia such as intrauterine growth restriction (IUGR) pregnancies. Endoglin expression was high at 4 to 9 weeks of gestation, when oxygen tension is low, and decreased after 10 weeks, when oxygen tension increases. Exposure of villous explants to low oxygen (3% O2) resulted in elevated expression of both membrane and soluble endoglin compared to standard conditions (20% O2). Moreover, addition of TGF-beta 3 to villous explants under low oxygen conditions increased the expression of endoglin compared to nontreated explants whereas addition of TGF-beta 3-neutralizing antibodies inhibited the low oxygen stimulatory effect on endoglin expression. Endoglin and soluble endoglin expression were significantly increased in placentas of IUGR singletons compared to controls and in the IUGR twin placentas relative to both the control co-twin and the normal twins. These data demonstrate that oxygen regulates the placental expression of endoglin via TGF-beta 3. Reduced placental perfusion leading to placental hypoxia might contribute to the increased expression of endoglin in IUGR pregnancies.

Increased insulin sensitivity and maintenance of glucose utilization rates in fetal sheep with placental insufficiency and intrauterine growth restriction

In this study we determined body weight-specific fetal (umbilical) glucose uptake (UGU), utilization (GUR), and production rates (GPR) and insulin action in intrauterine growth-restricted (IUGR) fetal sheep. During basal conditions, UGU from the placenta was 33% lower in IUGR fetuses, but GUR was not different between IUGR and control fetuses. The difference between glucose utilization and UGU rates in the IUGR fetuses demonstrated the presence and rate of fetal GPR (41% of GUR). The mRNA concentrations of the gluconeogenic enzymes glucose-6-phophatase and PEPCK were higher in the livers of IUGR fetuses, perhaps in response to CREB activation, as phosphorylated CREB/total CREB was increased 4.2-fold. A hyperglycemic clamp resulted in similar rates of glucose uptake and utilization in IUGR and control fetuses. The nearly identical GURs in IUGR and control fetuses at both basal and high glucose concentrations occurred at mean plasma insulin concentrations in the IUGR fetuses that were approximately 70% lower than controls, indicating increased insulin sensitivity. Furthermore, under basal conditions, hepatic glycogen content was similar, skeletal muscle glycogen was increased 2.2-fold, the fraction of fetal GUR that was oxidized was 32% lower, and GLUT1 and GLUT4 concentrations in liver and skeletal muscle were the same in IUGR fetuses compared with controls. These results indicate that insulin-responsive fetal tissues (liver and skeletal muscle) adapt to the hypoglycemic-hypoinsulinemic IUGR environment with mechanisms that promote glucose utilization, particularly for glucose storage, including increased insulin action, glucose production, shunting of glucose utilization to glycogen production, and maintenance of glucose transporter concentrations.

The pregnant sheep as a model for human pregnancy

Successful outcome of human pregnancy not only impacts the quality of infant life and well-being, but considerable evidence now suggests that what happens during fetal development may well impact health and well-being into adulthood. Consequently, a thorough understanding of the developmental events that occur between conception and delivery is needed. For obvious ethical reasons, many of the questions remaining about the progression of human pregnancy cannot be answered directly, necessitating the use of appropriate animal models. A variety of animal models exist for the study of both normal and compromised pregnancies, including laboratory rodents, non-human primates and domestic ruminants. While all of these animal models have merit, most suffer from the inability to repetitively sample from both the maternal and fetal side of the placenta, limiting their usefulness in the study of placental or fetal physiology under non-stressed in vivo conditions. No animal model truly recapitulates human pregnancy, yet the pregnant sheep has been used extensively to investigate maternal-fetal interactions. This is due in part to the ability to surgically place and maintain catheters in both the maternal and fetal vasculature, allowing repeated sampling from non-anesthetized pregnancies. Considerable insight has been gained on placental oxygen and nutrient transfer and utilization from use of pregnant sheep. These findings were often confirmed in human pregnancies once appropriate technologies became available. The purpose of this review is to provide an overview of human and sheep pregnancy, with emphasis placed on placental development and function as an organ of nutrient transfer.

Fetal effects of maternal supplementary oxygen during Caesarean section

PURPOSE OF REVIEW

This review summarises the current issues, knowledge and research on the effects of maternal supplementary oxygen therapy on the fetus during Caesarean section. This is a controversial subject since supplementary oxygen has the potential to confer both benefits and also harm to the fetus, depending on the circumstances.

RECENT FINDINGS

For elective Caesarean section, breathing room air under regional anaesthesia or 30% oxygen under general anaesthesia is not associated with either maternal or fetal hypoxia. A prolonged uterine-incision-to-delivery (U-D) interval of up to 310 s is not a major factor per se for development of fetal hypoxia or acidosis, and no benefits could be derived from breathing supplementary oxygen in this situation. Although it appears rational to provide supplementary oxygen in the presence of a hypoxic or compromised fetus, to achieve meaningful increases in fetal oxygenation, a very high inspired oxygen fraction (FiO2) is required. However, it still remains unclear whether this is beneficial for the fetus. The process of damage to the hypoxic fetus is one of oxidative stress mediated by free radicals generated during reperfusion (ischaemia-reperfusion injury). Independently, hyperoxia from breathing supplementary oxygen also induces formation of free radicals by direct mitochondrial electron transfer. Although hyperoxia could lessen the severity of fetal hypoxia, there is also a theoretical risk of an enhanced reperfusion injury. This issue has not been resolved in a clinical study, but an animal study reported enhanced formation of free radicals after an episode of fetal hypoxia in the group receiving supplementary oxygen.

SUMMARY

For elective Caesarean section, current evidence suggests that supplementary oxygen is unnecessary. For emergency Caesarean section, further data are required before a conclusion can be made for its beneficial and adverse effects. Improvement of fetal oxygenation should be the primary objective, and this is achievable in the short term by using a very high FiO2. Although there is also a possibility of an enhanced reperfusion injury, particularly in the preterm and non-labouring patients, further data are necessary before a conclusion can be made.

Placental HIF-1 alpha, HIF-2 alpha, membrane and soluble VEGF receptor-1 proteins are not increased in normotensive pregnancies complicated by late-onset intrauterine growth restriction

Inadequate trophoblast invasion and spiral artery remodeling leading to poor placental perfusion are believed to underlie the pregnancy pathologies preeclampsia (PE) and intrauterine growth restriction (IUGR). The main objective of this study was to investigate hypoxia-inducible transcription factor-alpha (HIF-alpha) and downstream genes (VEGF receptor-1) Flt-1 and soluble fms-like tyrosine kinase 1 (sFlt-1) proteins in IUGR placentas. Placentas from normal pregnant (NP; n = 18), PE (n = 18), and IUGR (n = 10) patients were investigated. Normotensive patients with IUGR delivered babies at >or= 37 wk of gestation with birth weights of <10% and asymmetrical growth. HIF-1 alpha, -2 alpha, Flt-1, and sFlt-1 protein, and mRNA were assessed by Western and Northern blot analyses, respectively. The results are expressed as ratios of the densitometric values for each pair of pathologic and normal placentas, a ratio of 1.0 indicating no difference. Comparable to our earlier studies, the PE/NP ratios for HIF-1 alpha, -2 alpha, and Flt proteins were significantly increased by 50-100% (all P < 0.01 vs. 1.0). Unexpectedly, the IUGR/NP ratios for HIF-1 alpha and -2 alpha proteins were 1.03 +/- 0.07 and 0.96 +/- 0.16, respectively, and for Flt and sFlt were 1.14 +/- 0.15 and 0.95 +/- 0.12, respectively (all P = not significant vs. 1.0). Northern blot analysis revealed comparable levels of HIF-alpha mRNA in abnormal and normal placentas. In contrast to PE, HIF-alpha proteins and regulated genes are not increased in placentas from normotensive pregnant women delivering small, asymmetrically grown babies >or= 37 wk of gestation. The absence of an increase in HIF-alpha protein is not due to insufficient HIF-alpha mRNA for protein synthesis. Thus, the placentas from women with PE and late IUGR are fundamentally different at the molecular level.

Development and mechanisms of fetal hypoxia in severe fetal growth restriction

Severe fetal growth restriction (FGR) is often associated with hypoxia. We studied FGR hypoxia in an experimental model which is produced by exposing pregnant ewes to a hyperthermic environment. The study utilized simultaneous measurements of several relevant factors, e.g., uterine and umbilical blood flows and O(2) uptakes. Sixteen ewes were divided equally into control (C) and hyperthermic (HT) groups. Hyperthermia (40 degrees C for 12h/35 degrees C for 12h; approximately 35% relative humidity, RH) was maintained for 80 days commencing at approximately 38 days gestational age (dGA term 147+/-3 days). All ewes were then placed in a control environment ( approximately 21 degrees C, 24h; approximately 30% RH) and studied at approximately 134 dGA. Mean HT placental and fetal weights were 39% and 45% of C, respectively (p<0.0001), umbilical O(2) uptake/kg fetus was 76% of C (p<0.01) and umbilical venous PO(2) was reduced (20.2 vs. 29.7 Torr, p<0.001). Contrary to the hypothesis that FGR hypoxia is due to maternal placental hypoperfusion, uterine flow was not reduced in relation to O(2) uptake. The uterine-umbilical venous PO(2) difference was enlarged (38 vs. 23 Torr, p<0.0001). This difference is the expression of a balance between developmental changes in placental structure and oxidative metabolism, which have opposite effects in terms of fetal oxygenation. We postulate that FGR hypoxia results from disproportionate underdevelopment of those changes which allow for a progressive increase in umbilical O(2) uptake.

Amnion degeneration over fetal placental surface vessels possibly resulting from focal hypoxia: a case report

The monoamnionic placenta of this twin gestation had focal amnion necrosis, but this was present only over the fetal surface vessels of one twin; this twin also developed cerebral atrophy. We hypothesize that this degeneration is due to a more severely reduced oxygen tension in its vessels. The placental amnion epithelium may undergo several degenerative processes, including amnion nodosum and changes due to meconium staining. Sonography had disclosed what appeared to be a dividing membrane, but this was not found at birth when monoamnionic twins with entangled cords presented. The amnion degeneration was present only over the large surface fetal vessels of the placenta of that twin who also developed central nervous system degeneration, and macrophage infiltration was confined to the same lesions. Focal hypoxia from entangling cords may have caused this defect.

Human fetal growth and organ development: 50 years of discoveries

Knowledge about human fetal growth and organ development has greatly developed in the last 50 years. Anatomists and physiologists had already described some crucial aspects, for example, the circulation of blood during intrauterine life through the fetal heart, the liver as well as the placenta. However, only in the last century physiologic studies were performed in animal models. In the human fetus, the introduction of ultrasound and Doppler velocimetry has provided data about the growth and development of the fetus and of the circulation through the different fetal districts. Moreover, in the last 2 decades we have learned about fetal oxygenation and fetal nutrient supply caused by the availability of fetal blood samples obtained under relatively steady state conditions. These studies, together with studies using stable isotope methodologies, have clarified some aspects of the supply of the major nutrients for the fetus such as glucose, amino acids, and fatty acids. At the same time, the relevance of placental function has been recognized as a major determinant of fetal diseases leading to intrauterine growth restriction. More recently, the availability of new tools such as 3-dimensional ultrasound and magnetic resonance imaging, have made possible the evaluation of the growth and development of fetal organs. This knowledge in the healthy fetus will improve the ability of clinicians to recognize abnormal phenotypes of the different fetal organs, thus allowing to stage fetal diseases.

Attenuated insulin release and storage in fetal sheep pancreatic islets with intrauterine growth restriction

We determined in vivo and in vitro pancreatic islet insulin secretion and glucose metabolism in fetuses with intrauterine growth restriction (IUGR) caused by chronic placental insufficiency to identify functional deficits in the fetal pancreas that might be caused by nutrient restriction. Plasma insulin concentrations in the IUGR fetuses were 69% lower at baseline and 76% lower after glucose-stimulated insulin secretion (GSIS). Similar deficits were observed with arginine-stimulated insulin secretion. Fetal islets, immunopositive for insulin and glucagon, secreted insulin in response to increasing glucose and KCl concentrations. Insulin release as a fraction of total insulin content was greater in glucose-stimulated IUGR islets, but the mass of insulin released per IUGR islet was lower because of their 82% lower insulin content. A deficiency in islet glucose metabolism was found in the rate of islet glucose oxidation at maximal stimulatory glucose concentrations (11 mmol/liter). Thus, pancreatic islets from nutritionally deprived IUGR fetuses caused by chronic placental insufficiency have impaired insulin secretion caused by reduced glucose-stimulated glucose oxidation rates, insulin biosynthesis, and insulin content. This impaired GSIS occurs despite an increased fractional rate of insulin release that results from a greater proportion of releasable insulin as a result of lower insulin stores. Because this animal model recapitulates the human pathology of chronic placental insufficiency and IUGR, the beta-cell GSIS dysfunction in this model might indicate mechanisms that are developmentally adaptive for fetal survival but in later life might predispose offspring to adult-onset diabetes that has been previously associated with IUGR.

Placental morphometry and Doppler flow velocimetry in cases of chronic human fetal hypoxia

OBJECTIVE

To investigate the structural basis of abnormal Doppler waveforms in the utero-placental circulations in cases of chronic fetal hypoxia.

STUDY DESIGN

Morphometric analysis was performed on placental samples from 58 pregnancies with abnormal Doppler waveforms in the uterine, placental and umbilical circulations at 32-34 weeks, and 10 pregnancies with normal waveforms.

RESULTS

The volume of placental villi reduced from 350.5 cm3 in controls to 286.4 cm3 (P<0.05) in the severest cases. The volume of the fetal capillaries reduced from 59.7 cm3 to 20.5 cm3 (P<0.05). These reductions were associated with increased placental infarction. The myometrial segments of the spiral arteries were severely constricted, demonstrating failure of physiological conversion secondary to deficient trophoblast invasion.

CONCLUSION

The placental vascular bed is greatly reduced in cases of chronic fetal hypoxia. We propose impaired placental perfusion causes oxidative stress and regression of the fetal vasculature, leading to fetal growth retardation and distress.

Placental phenotypes of intrauterine growth

The placenta is essential to nutrition before birth. Recent work has shown that a range of clearly defined alterations can be found in the placentas of infants with intrauterine growth restriction (IUGR). In the mouse, a placental specific knockout of a single imprinted gene, encoding IGF-2, results in one pattern of alterations in placenta structure and function which leads to IUGR. We speculate that the alterations in the human placenta can also be grouped into patterns, or phenotypes, that are associated with specific patterns of fetal growth. Identifying the placental phenotypes of different fetal growth patterns will improve the ability of clinicians to recognize high-risk patients, of laboratory scientists to disentangle the complexities of IUGR, and of public health teams to target interventions aimed at ameliorating the long-term adverse effects of inadequate intrauterine growth.

Prognostic Value of Umbilical Artery Doppler Studies in Unselected Preterm Deliveries

OBJECTIVE

To evaluate the prognostic value of umbilical artery Doppler studies in premature deliveries.

METHODS

In this cohort study of 582 singleton pregnancies delivered between 24 and 35 weeks of gestation, we evaluated the ratio of peak-systolic to end-diastolic (S/D) blood flow velocities in the umbilical artery of all the patients. The correlations among the results of the Doppler studies, short-term neonatal complications, and the infants' neurodevelopmental outcome at 2 years were studied by univariable and multivariable methods.

RESULTS

The prevalences of either neonatal death or cerebral palsy among the 266 (45.7%) growth restricted fetuses were 3.4% (3/88) in pregnancies with a S/D ratio below the 95th percentile, 4.9% (5/103) in pregnancies with a S/D at or above the 95th percentile, and 17.3% (13/75) in those with absent or reversed end-diastolic blood flow in the umbilical artery (P for trend = .001). The corresponding figures in the 316 pregnancies with adequate fetal growth were 6.4% (15/234) and 4.3% (3/69) among pregnancies with a S/D ratio below and at or above 95th percentile, respectively, whereas no cases of either neonatal death or cerebral palsy were recorded in the 13 pregnancies with adequate fetal growth and absent or reversed end-diastolic blood flow velocity (P for trend = .28; chi(2) for heterogeneity of linear trends compared with growth-restricted infants = 7.02, P = .008). In logistic regression, in pregnancies complicated by fetal growth restriction, absent or reversed end-diastolic blood flow in the umbilical artery was still associated with an increased risk of either neonatal death or cerebral palsy even after adjustment for gestational age and proportion of expected birth weight, (odds ratio 3.2, 95% confidence interval 1.18-8.66, P = .02).

CONCLUSION

Absent or reversed end-diastolic flow in the umbilical artery is an independent predictor of either neonatal death or cerebral palsy in preterm growth-restricted fetuses. In the absence of fetal growth restriction, umbilical artery Doppler study was associated with none of the infant outcome parameters studied.

Diminished beta-cell replication contributes to reduced beta-cell mass in fetal sheep with intrauterine growth restriction

Human fetuses with severe intrauterine growth restriction (IUGR) have less pancreatic endocrine tissue and exhibit beta-cell dysfunction, which may limit beta-cell function in later life and contribute to their increased incidence of noninsulin-dependent diabetes mellitus. Three factors, replication, apoptosis, and neoformation, contribute to fetal beta-cell mass. We studied an ovine model of IUGR to understand whether nutrient deficits lead to decreased rates of fetal pancreatic beta-cell replication, increased rates of apoptosis, or lower rates of differentiation. At 90% of term gestation, IUGR fetal and pancreatic weights were 58% and 59% less than pair-fed control, respectively. We identified a selective impairment of beta-cell mass compared with other pancreatic cell types in IUGR fetuses. Insulin and insulin mRNA contents were less than other pancreatic endocrine hormones in IUGR fetuses, as were pancreatic insulin positive area (42%) and beta-cell mass (76%). Pancreatic beta-cell apoptosis was not different between treatments. beta-cell capacity for cell cycling, determined by proliferating cell nuclear antigen (PCNA) immunostaining, was not different between treatment groups. However, the percentage of beta-cells actually undergoing mitosis was 72% lower in IUGR fetuses. These results indicate that in utero nutrient deficits decrease the population of pancreatic beta-cells by lengthening G1, S, and G2 stages of interphase and decreasing mitosis near term. Diminished beta-cell mass in IUGR infants at birth, if not adequately compensated for after birth, may contribute to insufficient insulin production in later life and, thus, a predisposition to noninsulin-dependent diabetes.

Developmental biology of the placenta and the origins of placental insufficiency

Defects in all the trophoblast-differentiating pathways--endovascular, interstitial and chorionic villous--play a role in the pathogenesis of early-onset intra-uterine growth restriction (IUGR). There are two types of extravillous trophoblast: endovascular trophoblast, that forms the definitive placenta by occlusion of the spiral arteriole at the implantation site, and interstitial extravillous trophoblast, responsible for the anatomical erosion of the distal spiral arteriole and the secretion of angiogenic and vasodilator signals to improve uterine blood flow. Defective endovascular erosion may render the basal plate inadequate to meet the demands of the fetus. Failed interstitial invasion of spiral arterioles could lead to failure of local angiogenic and systemic cardiovascular adaptation signals that could be the underlying basis for early-onset IUGR and pre-eclampsia. As debate persists regarding the relative importance of cord, stem and terminal villous pathology, the study of factors controlling trophoblast turnover from immature intermediate villi to conductance stem villi and gas-exchanging terminal villi, translation of our knowledge from mouse placental genetics into human placental development, and defining causes of thrombo-occlusive damage to the placenta would help our understanding of the pathophysiology of early-onset IUGR.

The relationship between transplacental O2 diffusion and placental expression of PlGF, VEGF and their receptors in a placental insufficiency model of fetal growth restriction

Placental growth factor (PlGF) and vascular endothelial growth factor (VEGF) are involved in placental angiogenesis through interactions with the VEGFR-1 and VEGFR-2 receptors. The placenta of pregnancies whose outcome is fetal growth restriction (FGR) are characterized by abnormal angiogenic development, classically associated with hypoxia. The present study evaluated the near-term expression of this growth factor family in an ovine model of placental insufficiency-FGR, in relationship to uteroplacental oxygenation. Compared to controls, FGR pregnancies demonstrated a 37% increase in uterine blood flow (FGR vs. control, 610.86+/-48.48 vs. 443.17+/-37.39 ml min(-1) (kg fetus)(-1); P<0.04), which was associated with an increased maternal uterine venous PO2 (58.13+/-1.00 vs. 52.89+/-1.26 mmHg; P<0.02), increased umbilical artery systolic/diastolic ratio (3.90+/-0.33 vs. 2.12+/-0.26, P<0.05), and fetal hypoxia (arterial PO2; 12.79+/-0.97 vs. 18.65+/-1.6 mmHg, P<0.005). Maternal caruncle PlGF mRNA was increased in FGR (P<0.02), while fetal cotyledon VEGF mRNA was reduced (P<0.02). VEGFR-1 mRNA was also reduced in FGR fetal cotyledon (P<0.001) but was not altered in caruncle tissue. Immunoblot analysis of PlGF and VEGF demonstrated single bands at 19,000 and 18,600 Mr, respectively. Caruncle PlGF concentration was increased (P<0.04), while cotyledon VEGF was decreased (P<0.05) in FGR placentae. The data establish that uterine blood flow is not reduced in relationship to metabolic demands in this FGR model and that the transplacental PO2 gradient is increased, maintaining umbilical oxygen uptake per unit of tissue. Furthermore, these data suggest that an increased transplacental gradient of oxygen generates changes in angiogenic growth factors, which may underline the pathophysiology of the post-placental hypoxic FGR.

Intralobular differences in antioxidant enzyme expression and activity reflect the pattern of maternal arterial bloodflow within the human placenta

The aim was to determine whether the activities and mRNA concentrations of antioxidant enzymes in human placental tissues reflect the prevailing oxygen tension or developmental maturity of the villi. Advantage was taken of contrasting gradients within lobules of the mature placenta. The central region is well-oxygenated compared to the periphery, owing to the direction of maternal blood flow. However, central villi are morphologically and enzymatically immature compared to peripheral villi. Activity of catalase (t=8.72, P< 0.001) and glutathione peroxidase (t=2.17,P< 0.05) was higher in central than peripheral villi, but no difference was detected for total superoxide dismutase (t=1.08, P> 0.05). The degree of change in catalase activity across the lobule correlated closely with the radius (r=-0.70, P< 0.01). The mRNA concentration was higher in the centre for catalase (t=2.81, P< 0.05) and for glutathione peroxidase (t=3.33, P< 0.05), but no differences were found for copper/zinc or manganese superoxide dismutase. In separate experiments, first trimester villi cultured under 10 per cent oxygen contained higher concentrations of catalase mRNA than controls maintained under 2.5 per cent oxygen. We conclude that the activities of catalase and glutathione peroxidase reflect gradients established by the pattern of maternal intralobular bloodflow, and that oxygen tension is one regulatory factor in vitro.

Carbon monoxide disposition and permeability-surface area product in the foetal circulation of the perfused term human placenta

In order to estimate the placental barrier to gas transfer, a novel carbon monoxide (CO) wash-in method was used to estimate the permeability-surface area (PS) product for the transfer of gas across the foetal circulation in the perfused human term placenta. The PS product for CO was 0.0096+/-0.006 ml/s/g or 0.012+/-0.007 ml/s/g using compartmental or Crone-Renkin analysis, respectively. Using this result and a published estimate of the placental capillary surface area, the permeability coefficient to CO across the foetal circulation was found to be approximately 4 x 10(-5)cm/s. This result is compatible with the hypothesis that the foetal circulation of the human placenta imposes a potentially significant barrier to gas transfer.

Cationic amino acid transporter activity in the syncytiotrophoblast microvillous plasma membrane and oxygenation of the uteroplacental unit

The purpose of this study was to determine whether there is any relationship between the activity of cationic amino acid transporters in the microvillous plasma membrane (MVM) of the syncytiotrophoblast and the oxygenation of the uteroplacental unit. Oxygenation data were obtained at the time of caesarean section from the uterine veins, the maternal radial artery and the umbilical vessels of 7 normal (AGA) and 13 intrauterine growth restricted (IUGR) pregnancies. Microvillous plasma membranes were isolated from the same placentas and the activity of the system y(+) and y(+)L cationic amino acid transporters determined by measuring (3)H- l -arginine uptake in the presence and absence of l -glutamine. In IUGR pregnancies uterine venous Po(2) was significantly higher (AGA=44.7+/-8.0 mmHg; IUGR=57.2+/-2.3 mmHg, P< 0.05) and umbilical venous Po(2) was significantly lower (AGA=33.4+/-3.0 mmHg; IUGR=25.1+/-2.0 mmHg, P< 0.05) than in AGA pregnancies. System y(+)L activity, but not system y(+) activity, was inversely correlated with uterine venous Po(2) (P< 0.01; r(2)=0.4) in AGA and IUGR pregnancies. In IUGR pregnancies without associated maternal pre-eclampsia, y(+)L activity, but not y(+) activity, was also directly related to the umbilical O(2) content difference (P< 0.01; r(2)=0.9). A significant negative correlation was found between system y(+) and the umbilical O(2) content difference in AGA pregnancies (P< 0.01; r(2)=0.9). Our data are consistent with the hypothesis that in IUGR fetuses uterine oxygenation is not reduced and can be increased. The inverse correlation between system y(+)L activity and uterine venous Po(2) and the correlations with umbilical venous-arterial O(2) content difference suggest a relationship between cationic amino acid transporter activity and oxygen tension in the uteroplacental unit.

Placental development in normal and compromised pregnancies-- a review

Intrauterine growth restriction (IUGR) is a significant cause of infant mortality and morbidity. It is now clear that IUGR infants exhibit higher rates of coronary heart disease, type 2-diabetes, hypertension and stroke as adults. Therefore, fetal growth not only impacts the outcome of the perinatal period, but also impacts adult well-being. The etiologies of IUGR are numerous, but are often associated with abnormalities in placental structure and function. The process of implantation and placentation requires the production of a plethora of growth factors, cell-adhesion molecules, extracellular matrix proteins, hormones and transcription factors. Many of these exhibit altered expression within the placenta of IUGR pregnancies. However, it has been difficult to fully assess their role during the development of placental insufficiency (PI) in the human, underscoring the need for animal models. Using an ovine model of PI-IUGR we have observed changes in the expression of vascular endothelial growth factor, placental growth factor, their common receptors, as well as angiopoietin 2 and its receptor, Tie 2. We found that changes in these growth factors can be associated with both acute and chronic changes in placental vascular structure and function. These studies and others are providing needed insight into the developmental chronology of placental insufficiency.