CHORIODECIDUAL AND MYOMETRIAL BLOOD-FLOW

Pre-eclampsia and Fetal Growth Restriction: How Morphometrically Different is the Placenta?

Both pre-eclampsia (PET) and fetal growth restriction (FGR) pose a heavy burden on fetal and maternal health and may disrupt pregnancy outcome. Using design based stereological techniques, placental vascular and villous morphology were assessed to determine the individual role played by both PET and FGR on placental growth during the third trimester. The following placentas delivered between 25 and 41 weeks of gestation were included into the study; controls (n=16), PET (n=20), FGR (n=17) and PET-FGR (n=16). Each placenta was uniformly randomly sampled and the sampled tissue processed to paraffin. Sections were stained with a CD34 antibody and the following morphometric parameters estimated: volumes, surface areas, length, diameters and the shape factor of the villous (terminal and intermediate) and vascular placental features. For stereologically estimated parameters pure PET had an effect on IVS and terminal villi volume only. FGR alone or when coexisting with PET contributed towards significant reductions in volumetric and surface area terminal villous and vascular features. FGR factors also contributed towards a significant reduction in the lengths of all parameters estimated and in the terminal villi diameter. Additionally, FGR was associated with a significant difference in shape factor indices for both intermediate and terminal villi. This study has shown that PET on its own has limited influence on the placental morphology studied, since the vascular features estimated do not differ stereologically from age matched normal controls. However, placental morphology is different between PET and PET-FGR and between PET-FGR and FGR. PET and FGR may have a cumulative effect on placental villous and vascular morphology as seen in the PET-FGR but there is no synergistic effect. These morphological abnormalities may have major physiological implications in terms of placental function and fetal growth.

A contemporary view of the human placenta

Our current knowledge of the human placenta is briefly reviewed. Particular stress is placed upon the considerable functional reserve capacity of the placenta, the unimportance of most visible abnormalities of the placenta, the lack of any evidence that the placenta ages during gestation and the lack of significance of placental weight. The effects on the placenta of infection and of maternal cigarette smoking are considered and the concept of placental insufficiency critically discussed. It is concluded that most cases of 'placental insufficiency' are, in reality, examples of maternal vascular insufficiency resulting from inadequate placentation during the early stages of pregnancy.

The use of Doppler ultrasound in the study of fetal cardiovascular physiology

Doppler velocimetry of the uteroplacental and umbilical arteries provides an opportunity for the safe, reproducible and repeatable study of these circulations and already has led to an increased knowledge of the pathophysiology of pregnancy induced hypertension and intra-uterine growth retardation. This technique, which has only recently been introduced widely into obstetrics, also permits the study of the cardiovascular effects on the fetus of maternally administered drugs. The use of Doppler for these purposes is illustrated with particular reference to intra-uterine growth retardation and the use of the antihypertensive drugs, atenolol and nifedipine.

Lipid peroxidation in pregnancy: new perspectives on preeclampsia

Basic research during the past two decades has led to increased awareness of the role of lipid peroxidation in various physiologic and pathophysiologic processes. A number of reports indicate that preeclampsia is associated with elevated blood levels of lipid peroxidation products. In view of its potentially destructive character, uncontrolled lipid peroxidation has been suggested as an etiologic factor in preeclampsia. The present article summarizes current information regarding the occurrence of lipid peroxidation in normal and preeclamptic pregnancy. Recent progress concerning our understanding of the process of lipid peroxidation and its role in cardiovascular disease is also reviewed. This information is used to discuss potential mechanisms by which lipid peroxidation might contribute to the pathogenesis of preeclampsia.

The uterine artery blood flow velocity waveform in pathological pregnancy

Uterine artery blood flow velocity waveforms (FVW) were recorded longitudinally in 41 women with undisturbed pregnancy as well as in 32 women with complicated pregnancy at 4-week intervals from a gestational age of 18 weeks onwards. Of these women, four did not complete the study. In a second group of 76 patients at least one FVW was recorded after admission to the obstetrical department because of complicated pregnancy. The Pulsatility-Index (PI) for normal pregnancy was based on the results of the 41 women with undisturbed pregnancy (Mulders et al. (1988) Early Hum. Dev., 17, 55-70). The complete study group (n = 145) was divided in two groups, based on the value of the last measured uterine artery PI before delivery in the abnormal PI group (PI greater than or equal to 1.02 before 32 weeks or PI greater than or equal to 0.91 after 32 weeks, n = 38) hypertension, fetal distress during pregnancy, premature delivery, small for gestational age babies (SGA) and lower placental weight were all significantly increased. In each of the groups of patients with either SGA, fetal distress during pregnancy, pre-existing hypertension with proteinuria and pregnancy-induced hypertension with or without proteinuria the mean PI was significantly increased as compared to the results in normal pregnancy. Sensitivity and specificity of the last uterine artery PI for the detection of SGA and/or fetal distress during pregnancy were 48.8% and 82.7%, respectively. The longitudinally studied women (n = 73) were divided in two groups, based on uterine artery PI before 32 weeks of gestation; in the abnormal PI group (PI greater than or equal to 1.02, n = 12) pregnancy was more complicated by premature delivery and low birth weight. Sensitivity for the early prediction of pathological pregnancies (at least one pathological phenomenon as mentioned above) was 30.4%, whereas specificity was 90.0%.

Placental glycolysis and energy metabolism in preeclampsia

We examined the possibility that in preeclampsia complicated by fetal growth retardation, placental energy state is low either because of impaired glycolysis or because of ischemia resulting from reduced maternal placental blood flow. Concentrations of pyruvate and lactate, but not of glycogen and glucose, were significantly low in placentas of mothers with severe preeclampsia, supporting previous indirect evidence of inhibited glycolysis. Nevertheless, direct measurements of adenine nucleotide concentrations did not indicate reduced placental energy level in the preeclamptic placentas. This along with a lack of change of the ratio of lactate/pyruvate concentration (an indication of the redox state of cytoplasmic reduced nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide) is also evidence against the hypothesis of general placental ischemia leading to energy deficiency. However, as glycolysis is an important source of precursors, particularly pyruvate, for synthesis of amino acids and lipids, these results suggest that there is a significant metabolic abnormality in placentas of mothers with severe preeclampsia.

Do placental weights have clinical significance?

This study attempted to determine if placental size has implications for fetal/neonatal health and for subsequent childhood growth and development. 38,351 placentas were trimmed and weighed in a standardized way. The following factors were found to be associated with low placental weight: low maternal pregravid body weight, low pregnancy weight gain, high maternal hemoglobin levels during pregnancy, gestational hypertension, paid employment outside the home during pregnancy, and low parity. Taking these factors into consideration, placentas that were underweight for birth weight were associated with high hemoglobin values in neonates and lower-than-expected body size in later childhood. Overweight placentas, largely a result of villous edema, were associated with the following neonatal evidences of acute antenatal hypoxia: low Apgar scores, the respiratory distress syndrome, neurologic abnormalities, and neonatal death. Some of the neurologic abnormalities persisted so that at patient age of 7 years, they were 33 per cent more frequent when placentas had been overweight than when they had been of normal weight (P less than .001).

Obstetric factors associated with cord blood gas values at birth

Values of pH, base deficit and Pco2 in 885 unselected samples of umbilical blood collected at birth were related to pregnancy and delivery details. An increase in acidosis in both umbilical vein and artery was associated with placental abruption, maternal pethidine, pre-eclampsia, primigravidity, vaginal operative delivery for fetal distress and a long second stage of labour. Increased acidosis in arterial, but not venous, blood occurred with cord entanglement, vaginal breech delivery, postmaturity, high birthweight and a long first stage of labour. The relationship between obstetric factors and the acid-base state of the neonate suggests a possible role for cord blood gas measurements in assessing the results of obstetric practice.

Inadequate maternal vascular response to placentation in pregnancies complicated by pre-eclampsia and by small-for-gestational age infants

An examination of the maternal vascular response to placentation shows that physiological changes in the placental bed normally extend from the decidua into the inner myometrium. In pre-eclampsia and in a proportion of pregnancies with small-for-gestational age infants (SGA) the physiological changes are restricted to the decidual segments alone. In addition, complete absence of physiological changes throughout the entire length of some spiral arteries is seen in pre-eclampsia and SGA. This new observation is confirmed in a study of basal plates of placentas from abnormal pregnancies. Intraluminal endovascular trophoblast may be seen in the placental bed spiral arteries in the third trimester in pre-eclampsia and SGA, a feature not seen beyond the second trimester in normal pregnancy. These findings point to a defect in the normal interaction between migratory trophoblast and maternal uterine tissues in pre-eclampsia and in SGA.

The placental bed biopsy: review from three European centers

This review derives from extensive experience with the placental bed biopsy technique in three centers over the last 30 years. A placental bed biopsy, usually taken at cesarean section, must include basal decidua and subjacent myometrium from the central zone of the placental site. Attention is drawn specifically to the sampling errors and to the pitfalls in morphologic interpretation of tissues, both maternal and fetal, that are continuously changing throughout the course of pregnancy. The features of the normal placental bed and of vascular lesions in pathologic pregnancies are briefly reviewed. Extension and elaboration of the technique and its more widespread use could contribute to the elucidation of many of the unresolved problems in human pregnancy.

Vasoactive intestinal polypeptide as a neurotransmitter in the female genital tract

Vasoactive intestinal polypeptide (VIP) has been demonstrated in nerve fibers of the female genital tract localized in synaptic vesicles. The VIP-containing nerve fibers seem to innervate nonvascular smooth muscle, blood vessels, and epithelial cells. Evidence is accumulating that VIP fulfills a number of the classical criteria to be a neurotransmitter in the female genital tract. It is likely that VIP is the mediator of genital functions, which are controlled by noncholinergic, nonadrenergic nerve fibers. VIP seems to play a role in the local nervous control of uterine smooth muscle, e.g., opening of the uterotubal junctions, and to be involved in vasodilatation in the uterus as wells as the vagina. In conclusion, a third or peptidergic division of the autonomic nervous system seems to participate in the nervous control of reproduction.

Invited review. A contemporary approach to placental pathology

A brief description is given of the significance of gross and histological abnormalities of the placenta. The question of placental ageing is discussed and the possible ill-effects of inflammation and immune-mediated damage to the placenta considered. Finally, the pathology of the utero-placental vasculature is outlined, and the view is expressed that most cases of apparent 'placental insufficiency' are, in reality, due to maternal vascular insufficiency.

Measurement of myometrial blood flow in rabbits by washout of xenon-133 after atraumatic local labelling

In vivo experiments were performed on the uterine tissue of non-pregnant estradiol treated rabbit anesthetized with sodium pentobarbitone. The average blood flow calculated from the washout of Xenon-133 after atraumatic labelling from the uterine surface was 25.4 ml . min-1.(100 g)-1 (range 7.4-66.6), and after local injection of a tracer in isotonic saline directly into the myometrium 24.4 ml.min-1.(100 g)-1(range 8.7-45.3). During the experiments a monoexponential washout curve was found for the whole washout process both after atraumatic labelling and when the injected volume was 5 microliter. No trauma of injection was observed using this injection volume. The results support the applicability of a monocompartmental model for the washout of inert gas from the myometrium. Thus myometrial blood flow can be calculated from the Xenon-133 washout rate at any time interval during the washout process.

An ultrastructural and ultrahistochemical study of the human placenta in maternal pre-eclampsia

At the electronoptical level the placental villi of the pre-eclamptic woman are characterized by focal syncytial necrosis, loss and distortion of microvilli, dilatation of syncytial rough endoplasmic reticulum, decreased syncytial pinocytotic activity, a reduced number of syncytial secretory droplets, cytotrophoblastic hyperplasia, degeneration of occasional cytotrophoblastic cells, thickening of the trophoblastic basement membrane and the presence of small fetal capillaries with bulbous endothelial cells. Ultrahistochemical studies show reduced alkaline phosphatase and dehydrogenase activity in the syncytiotrophoblast but an increased acid phosphatase activity. It is suggested that all the observed morphological abnormalities, with the exception of cytotrophoblast cell degeneration, are explicable solely on the basis of utero-placental ischaemia and that no other aetiological factor need be invoked: the cause of the cytotrophoblast cell degeneration is, however, unknown. The ultrastructural findings indicate that there is a decrease in the transfer and synthetic activity of the trophoblast and that cellular respiration is also probably depressed. Nevertheless, there is some evidence that changes of a compensatory nature, designed to limit the effects of the tissue damage, are brought into play.

Placental intervillous blood flow measured by inhaled 133Xe clearance in relation to induction of epidural analgesia

A method of determining placental intervillous blood flow (IBF) using an inhaled 133Xe technique is described. The method was used to investigate the effect on IBF of epidural analgesia with an initial dose of 37.5 mg bupivacaine. There was no statistically significant reduction in IBF following the initial dose of bupivacaine in spite of a small but statistically significant reduction in mean blood pressure. There was no significant correlation between the change in mean blood pressure and the percentage change in IBF following epidural block although the single largest percentage reduction in IBF was associated with the largest fall in mean blood pressure.

Causes of the excessive rates of perinatal mortality and prematurity in pregnancies complicated by maternal urinary-tract infections

The study was undertaken to determine the causes of the more frequent pre-term deliveries, fetal and neonatal deaths associated with maternal urinary-tract infections during pregnancy. The combined perinatal mortality rate for eight common placental and fetal disorders was 42 per thousand births in the infected vs. 21 per thousand in the noninfected, owing to a greater mortality from noninfectious placental and fetal disorders in the gestations with the urinary-tract infections (P less than 0.001). All the mortality excess took place when the urinary-tract infections occurred within 15 days of delivery. Death rates were highest when the urinary-tract infections coexisted with maternal hypertension and acetonuria.Hydramnios, amniotic-fluid bacterial infections and abruptio placentae were responsible for two thirds of the more frequent preterm deliveries in the pregnancies complicated by urinary-tract infections.

Ultrastructure of the placenta in prolonged pregnancy

An electron-microscopic study has shown that in placentae from prolonged pregnancies there is hyperplasia of the villous cytotrophoblastic cells, degeneration of occasional isolated cytotrophoblastic cells, a paucity of syncytial microvilli in some areas and microvillous proliferation in others, abnormalities of microvillous form, focal syncytial necrosis, dilatation of syncytial endoplasmic reticulum, decreased synctial pinocytic activity, a reduced size and number of syncytial mitochondira, thickening of the trophoblastic basement membrane and contraction, blebbing and vacuolation of endothelial cells of the stromal foetal villous capillaries. Many of these morphological changes indicate that there is, in prolonged pregnancy, a decline in trophoblastic functional activity but it is suggested that this is due, not to placental senescence, but to a relatively mild, sustained uteroplacental ischaemia. Although there is morphological evidence to suggest that compensatory mechanisms come into play to limit the effects on the placenta of uteroplacental ischaemia the changes in the foetal capillaries, which are of unknown pathogenesis, will result in decreased foetal perfusion of the placenta and thus restrict still further adequate materno-foetal transfer.

Fetal growth retardation and the arteries of the placental bed

The morphology of the placental bed spiral arteries was studied in 68 pregnancies complicated by fetal growth retardation and in 40 pregnancies with a normally grown fetus. When the birth weight was normal the extent and depth of physiological vascular changes were normal except in those pregnancies complicated by pre-eclampsia. When the birth weight was low and the mothers were normotensive the extent and depth of physiological vascular changes were either normal or restricted, and in all patients with hypertension and a baby with low birth weight the physiological changes were restricted to the decidual segments of the spiral (uteroplacental) arteries. Acute atherosis was only found in pregnancies complicated by hypertension, particularly if there was proteinuria. We do not believe that there exists an arteriopathy which is common to hypertensive and normotensive pregnancies complicated by fetal growth retardation.

Relation of plasma oestriol to changes in blood pressure in pregnant patients with hypertension

Serial plasma oestriol levels were determined by radioimmunoassay in 24 patients with severe hypertension in pregnancy. No significant correlation could be found between plasma oestriol and percentage change in diastolic blood pressure. It seems unlikely that hypotensive therapy significantly improves fetoplacental function.

Measurement of intervillous and myometrial blood flow by an intravenous 133Xe method

A new 'non-invasive' method for measuring intervillous and myometrial blood flow is presented. After 2 mCi of 133Xe in physiological saline was injected intravenously the patient held her breath for 20 seconds. The tracer entered the placenta as a short bolus and its removal was followed with a scintillation detector. Intervillous and myometrial blood flow per unit volume was calculated from the two-exponential curve. The mean +/-SD intervillous flow in normal pregnancy was 135+/-49 ml/minute/100 ml, the corresponding half time being 0-56+/-0-16 minutes. The myometrial flow was 7-7+/-2-5 ml/minute/100 g. The method gave reproducible results and took only 20 minutes to perform. The dose of radiation to the mother was less than 1 mrad.

The metabolic clearance rate of dehydroisoandrosterone sulfate. IV. Acute effects of induced hypertension, hypotension, and naturesis in normal and hypertensive pregnancies

In the present study, the metabolic clearance rate of dehydroisoandrosterone sulfate (MCRDS) decreased in normotensive gravidas during short-term studies utilizing angiotensin II-induced elevation of blood pressure. Therapy with hydralazine hydrochloride in chronic hypertensive gravidas resulted in a decrease in blood pressure and an accompanying decrease in the MCRDS. A variable response was observed in the apparent volume of distribution of DS (AVDDS) during therapy with hydralazine hydrochloride. Decreases in MCRDS also occurred in chronic hypertensive gravidas following therapy with 40 mg. of intravenously administered furosemide despite a failure of blood pressure to be altered. The AVDDS increased in four of five patients receiving furosemide, suggesting a possible direct action of furosemide upon vascular smooth muscle.

[Studies on placental blood flow under drug induced hypertension (animal experiments) (author's transl)]

Placental blood-flow rates in rabbits were measured by the indirect method of local apparent conductivity. In our experiments, hypertension was produced by injection or infusion of hypertensive drugs. As a result of hypertension we observed a marked decrease in placental blood flow. Vasoconstriction seems to be the pathophysiologic mechanism causing the reduced blood flow rate. Accordingly, the placenta may not be considered as a "priviledged organ" in circulatory regulations. In our experiments, placental ischemia subsequently to ligatures did not produce hypertension so that the production of a placental pressor-substance could not be demonstrated. If we assume a circulus vitiosus hypertension-placental ischemia-hypertension, the hypertension seems to be the primary cause.

Placental scanning with computer-linked gamma camera to detect impaired placental blood flow and intrauterine growth retardation

By retrospective analysis of 65 placental localization studies by a computer-linked gamma camera the isotope studies by a computer-linked gamma camera the isotope uptake patterns were correlated with the eventual outcome of the pregnancies. The uptakes by anterior and lateral placentae were reduced in pregnancies which resulted in growth-retarded babies and statistically unrelated to the gestation of the pregnancy. This simple representation of placental blood flow could be a clinically useful index of placental function.

Pyridoxal phosphate and hypertensive disorders of pregnancy

Pyridoxal phosphate (vitamin B6) concentrations in peripheral and cord blood obtained at the time of delivery were measured in 30 women. The average plasma concentration in nine women with normal pregnancy was 4.3 ng. per milliliter; in 10 women with pre-eclampsia, 3.3 ng. per milliliter; and in nonpregnant women, 17 ng. per milliliter. The average cord blood plasma concentration of normal infants was 28.4 ng. per milliliter, whereas that of infants of pre-eclamptic mothers was 12.2 ng. per milliliter. This twofold difference in the cord plasma concentrations was statistically significant (p smaller than 0.001). Pyridoxal phosphate concentrations in the infants' cord plasma were increased in all pregnancies studied by administration of pyridoxine either orally or intravenously. These findings together with other data, demonstrating (1) that B6 deficiency during pregnancy may lead to abnormal neurologic development in experimental animals and (2) that brain development in infants of toxemic mothers may be retarded, suggest that dietary supplementation with vitamin B6 should be instituted in women at high risk for development of toxemia of pregnancy.

Successful use of oral diazoxide in the treatment of severe toxaemia of pregnancy

Treatment with oral diazoxide for periods of 4 to 10 weeks in hospital allowed adequate control of hypertension with continuation of fetal growth in four patients with severe toxaemia. Two were insulin-dependent diabetics and one of these suffered from renal failure. In all patients albuminuria diminished markedly, while the fluid retention was controlled with frusemide. Three pregnancies were successfully terminated by lower segment caesarean section and in the remaining case vaginal delivery resulted in the birth of a healthy baby. Control of blood sugars presented no problems in the diabetic patients. Only minimal adjustments of insulin dosage were required. One of the non-diabetic patients developed mild hyperglycaemia which responded to tolbutamide. The babies, ranging in age from 5 to 12 months, have continued to thrive.