Placental aging monitored by gray scale echography

Ultrasound evaluation of the placenta in healthy and placental syndrome pregnancies: A systematic review

INTRODUCTION

An antepartum screening method to determine normal and abnormal placental function is desirable in the prevention of maternal and fetal pregnancy complications. Placental appearance can easily be obtained and evaluated using 2D ultrasonography, but surprisingly little is known about the change in placental appearance during gestation. Aim of this systematic review was to describe the antepartum placental appearance in placenta syndrome (PS) pregnancies, and to compare this to the appearance in healthy pregnancies.

METHODS

A systematic review investigating placental thickness, -lakes and/or -calcifications by ultrasound examination in both uncomplicated (reference group) and PS pregnancies in relation to gestational age was performed. English literature was searched using PubMed (NCBI), EMBASE (Ovid) and the Cochrane Library, from database inception until September 2020. Data on placental thickness was presented as a continuous variable or as the proportion of abnormal placental thickness. Data on placental lakes and -calcifications was presented as prevalence (%). There was no restriction applied on the definition of placental lakes or -calcifications. Due to heterogeneity, pooling of the results was not performed.

RESULTS

A total of 28 studies were included describing 1719 PS cases; consisting of 370 (21 %) cases with preeclampsia or pregnancy induced hypertension, 1341 (78 %) cases with fetal growth restriction (FGR) or small for gestational age (SGA), and 8 (1%) cases with combined clinical expressions. In addition, the reference group comprised 3315 pregnant women. Placental thickness showed an increase between the first and second trimester, which was higher in PS- compared to uncomplicated pregnancies. Placental lakes were frequently observed in FGR and SGA pregnancies, especially in the second trimester. Grade 3 calcifications were most prominent in the PS pregnancies, specifically in the late second and third trimester. Moreover, in the reference group, no grade 3 calcifications were reported before 35 weeks of gestation.

CONCLUSION

Placental appearance in PS-pregnancies shows higher placental thickness and greater presence of placental lakes and -calcifications compared to uncomplicated pregnancies. Standardized definitions of (ab-)normal placental appearance and longitudinal research in both healthy and complicated pregnancies are needed to improve personalized obstetric care.

A role for cellular senescence in birth timing

Senescence contributes to the local and systemic aging of tissues and has been associated with age-related diseases. Recently, roles for this process during pregnancy have come to light, the dysregulation of which has been associated with adverse pregnancy outcomes such as preterm birth. Here, we summarize recent advances that support a role for senescence in birth timing and propose new aspects of study in this emerging field.

No correlation between ultrasound placental grading at 31-34 weeks of gestation and a surrogate estimate of organ function at term obtained by stereological analysis

We test the experimental hypothesis that early changes in the ultrasound appearance of the placenta reflect poor or reduced placental function. The sonographic (Grannum) grade of placental maturity was compared to placental function as expressed by the morphometric oxygen diffusive conductance of the villous membrane. Ultrasonography was used to assess the Grannum grade of 32 placentas at 31-34 weeks of gestation. Indications for the scans included a history of previous fetal abnormalities, previous fetal growth problems or suspicion of IUGR. Placentas were classified from grade 0 (most immature) to grade III (most mature). We did not exclude smokers or complicated pregnancies as we aimed to correlate the early appearance of mature placentas with placental function. After delivery, microscopical fields on formalin-fixed, trichrome-stained histological sections of each placenta were obtained by multistage systematic uniform random sampling. Using design-based stereological methods, the exchange surface areas of peripheral (terminal and intermediate) villi and their fetal capillaries and the arithmetic and harmonic mean thicknesses of the villous membrane (maternal surface of villous trophoblast to adluminal surface of vascular endothelium) were estimated. An index of the variability in thickness of this membrane, and an estimate of its oxygen diffusive conductance, were derived secondarily as were estimates of the mean diameters and total lengths of villi and fetal capillaries. Group comparisons were drawn using analysis of variance. We found no significant differences in placental volume or composition or in the dimensions or diffusive conductances of the villous membrane. Subsequent exclusion of smokers did not alter these main findings. Grannum grades at 31-34 weeks of gestation appear not to provide reliable predictors of the functional capacity of the term placenta as expressed by the surrogate measure, morphometric diffusive conductance.

Placental lakes on sonographic examination: correlation with obstetric outcome and pathologic findings

PURPOSE

The aim of this study was to compare pregnancy outcome and pathologic findings in cases of placental lake visualized on sonography in pregnancies without concurrent fetal or maternal disease.

METHODS

Placental aspect was evaluated sonographically in 4,106 singleton pregnancies without maternal or fetal disease at between 15 and 34 weeks3 gestation. Fifty-nine cases presenting with placental lakes were followed through the end of pregnancy. Obstetric outcome was compared with that of cases with sonographically normal placental aspects (n=37). Macroscopic and microscopic examinations for pathology were also performed in a few cases in both groups.

RESULTS

Placental lakes were present in 2.2% (92/4,106) of the cases. No statistically significant difference was observed in birth weight, gestational age at delivery, adverse obstetric outcome, and macroscopic or microscopic results between the control and study groups.

CONCLUSION

Our findings do not seem to indicate an increase in the risk for an adverse pregnancy outcome in cases presenting with placental lakes.

Forty years of obstetric ultrasound 1957-1997: from A-scope to three dimensions

In this article, we record the history of obstetric ultrasound as it developed worldwide in the second half of the twentieth century. The technological advances during this period saw the evolution of equipment from the original adapted metal flaw detectors producing a simple A-scan to the modern, purpose built, real-time colour flow machines with three-dimensional capability (Fig. 1). Clinically, ultrasound began as a research tool, but the poor quality of the images led to the ridicule of many of the early investigators. However, because of their perseverance, ultrasound developed into an imaging modality providing immense diagnostic capabilities and facilitating with precision many invasive procedures, diagnostic and therapeutic, both of which have made significant contributions to patient care. In this history, we recall the people, the personalities, and the problems they encountered during the development of ultrasound and how these problems were resolved, so that ultrasound now is available for use in the care of pregnant women throughout the developed world.

Sonographic, stereological and Doppler flow velocimetric assessments of placental maturity

OBJECTIVE

To determine whether sonographic assessments of increasing placental maturity are associated with changes in the theoretical diffusing capacity of the organ and with changes in vascular resistance.

DESIGN

Placental maturity was assessed sonographically in 10 organs: five were classified as completely immature and five as completely mature. Doppler flow velocimetric recordings were obtained shortly before delivery performed by elective caesarean section. Placental biopsies taken immediately after delivery were analysed stereologically.

RESULTS

No differences were observed in either placental weight or volume, but the morphometric diffusing capacity of the villous membrane was 40% higher in the mature than in the immature placentas. Doppler indices did not alter with increasing placental maturity.

CONCLUSIONS

Normal term placentas differ significantly in their diffusion characteristics, even when organ weight and volume remain constant. Umbilical vascular resistance may be heavily influenced by the number of parallel circulatory units offered by the placental lobules.

Intraplacental sonolucent spaces: incidences and relevance to chorionic villus sampling

Detailed ultrasound examination of the placentae from 293 consecutive women requesting first-trimester chorionic villus sampling (CVS) showed evidence of intraplacental sonolucent spaces with varying density in 42.3 per cent of these placentae. Their presence, however, did not complicate the subsequent course of these women's pregnancies. Their prime significance relates to CVS, where inadvertent entry into these areas can lead to bleeding and contamination of the villus specimens with blood. A search for these spaces should be made before sampling, and when present, they should be avoided wherever possible.

Perfusion fixation for placental morphologic investigation

Fifty placentas were collected after vaginal delivery or cesarean section from normal and abnormal pregnancies and were fixed under different conditions of perfusion using a peristaltic roller pump. In each case a physiologic-heparin perfusate was used for less than 10 minutes, followed by a buffered solution of glutaraldehyde-formaldehyde. The best results were obtained with placentas from cesarean sections perfused immediately after delivery with a pressure maintained under 60 mm Hg. Placentas of this group were fixed within 30 minutes and electron microscopy demonstrated good preservation of cellular ultrastructure. Perfusion fixation could be performed up to 6 hours after delivery with satisfactory histologic results. In these cases, electron microscopy revealed ischemic changes 10 minutes after delivery and severe necrosis 1 hour after delivery. When the perfusion pressure was maintained over 60 mm Hg, diffuse damage of the villous morphology was observed. Histomorphometric analysis showed significant differences between terminal villi from nonperfused (immersed-fixed) placentas and perfused-fixed placentas. The mean barrier and trophoblastic thicknesses and the mean volume fraction of trophoblast were significantly (P less than .001) increased in the nonperfused group compared with the perfused group.

Ultrasonographic assessment of placental abnormalities

Current ultrasonographic techniques offer a novel approach for the identification of a wide variety of placental abnormalities usually described postnatally by the pathologist. Placental vascular lesions, placental tumors, and abnormal placentation are potentially associated with perinatal complications and their diagnosis in utero may influence the pregnancy management. An ultrasonographic classification of placental lesions that is based on their location, size, echogenicity, and number is proposed. Repeated ultrasonographic examination, together with biologic investigations, is important for the prenatal differential diagnosis of most these lesions and for full understanding of their pathophysiologic characteristics and significance.

Ultrasonographically observed preterm grade III placenta and perinatal outcome

Ultrasound studies of placenta were conducted in 270 singleton normal pregnancies. Women were enrolled between 31 and 34 weeks of gestation and were followed up for the outcome of pregnancy. Women with grade III placental maturity comprised the study group (n = 64) and those with grade I placenta were enrolled as control group (n = 206). Another 100 normal women were enrolled to note the prevalence of grade III placenta at term. There was an increased incidence of intrauterine growth retardation (6.20%) and fetal distress (7.8%) in the study group compared with the control group (nil), which was statistically significant. The incidence of low birth weight was also higher (34.37%) in the study group compared with the control group (22.33%). Three women in the study group developed preeclampsia at subsequent follow up visit but none in control group (P less than 0.01). Prevalence rate of grade III placenta at term was 28%. In view of these findings preterm grade III placenta is found to be a sensitive predictor of poor perinatal outcome.

The value of ultrasonic placental grading: no correlation with intrauterine growth retardation or with maternal smoking

In a prospective study the usefulness of placental grading in detecting IUGR has been evaluated. Those who were echoscopically examined within one week before delivery were taken into the study (n = 137). Changes in placental tissue increased clearly as pregnancy progressed and in 42% (57/137) the placentae reached Grade III. Increasing placental grading is associated with normal maturation of the placenta. Post partum examination of the placenta correlated well with the echoscopic picture (accuracy = 80.5%). No relationship was found in an unselected group between Grade III and IUGR at term. When a Grade III placenta was first seen before 36 weeks, in three out of five cases a growth retarded neonate was born. The effects of maternal smoking habits during pregnancy on birth weight and placenta were examined. There were no significant differences in mean placental weight, placental ratio and placental grading as the amount of cigarettes increased. The mean birth weight and birth weight percentile decreased significantly when the mother smoked more than 10 cigarettes per day.

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

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

The ultrasound display of intervillous circulation

An ultrasonographic study of acoustic holes in the placenta shows that these contain maternal blood. The pattern of the maternal circulation can be visualized by ultrasonography, maternal blood entering the intervillous space in a continuous fashion with only a slight pulsatile pattern. Stasis of maternal blood and intervillous thrombus formation can also be distinguished.

An anatomic basis for ultrasound images of the human placenta

Placentas after uneventful pregnancies were perfused under physiologic pressure in the fetal vessels, expanded to their predelivery volume, fixated with 4% formaldehyde, and compared to their ultrasound images in pregnancy. The placentas showed a side arrangement of the fetal cotyledons in contact with the basal plate. The centers of the cotyledons showed an empty space in which the spiral arteries ended. These spaces in the placenta corresponded with transsonic areas of ultrasound. The central spaces were surrounded by a relatively dense shell of villi containing the more or less fibrotic stem villi. This explained the areas of increased echo-density, as seen by ultrasound during the last trimester of pregnancy. The fetal cotyledons, composed of a central cavity and a dense villous shell, were separated by a reticular area. The veins ended at the basal plate in these intercotyledonary areas.

Placental ultrasonographic biochemical and histochemical studies in human fetuses affected with Niemann-Pick disease type A

Placental ultrasonographic, bio- and histochemical studies were performed on four unrelated fetuses affected with Niemann-Pick disease Type A, following prostaglandin-induced abortion at about the 19th week of gestation. An accumulation of sphingomyelin in the placentae of affected fetuses indicates the essential role of the enzyme sphingomyelinase, even during the early stages of gestation. A fair correlation between histochemical localization of sphingomyelin in the placentae and ultrasonographic findings was found, indicating the value of ultrasonic echo wave information in the diagnosis of metabolic disorders.

The relationship of placental grade, fetal lung maturity, and neonatal outcome in normal and complicated pregnancies

Ultrasonically diagnosed maturity changes in the placenta, Grades 0 to III, have been previously shown to correlate with fetal lung maturity. In a prospective study of 230 term and preterm complicated pregnancies, we compared the relationship between sonographic placental grading, amniotic fluid phospholipids, and neonatal outcome. The frequencies of gestational age less than 38 weeks, lecithin/sphingomyelin (L/S) ratio less than 2.0, negative phosphatidylglycerol, and neonatal hyaline membrane disease were found to decrease as placental grade advanced from 0 to III. Patients were divided into subgroups on the basis of maternal complications. In patients with Grade III placentas, the frequencies of gestational age less than 38 weeks and L/S ratio less than 2.0 were significantly increased when the subgroup of patients with chronic hypertension was compared individually to both of the subgroups, repeat cesarean section deliveries, and Classes A, B, and C diabetes mellitus (both with p less than 0.05) All three infants who developed hyaline membrane disease in association with Grade III placentas were from pregnancies of less than 38 weeks complicated by chronic hypertension. These findings suggest that the presence of a Grade III placenta is affected by both gestational age and pregnancy complications. Hence, when an elective cesarean section delivery is being planned near term gestation, a Grade III placenta is a reliable predictor of lung maturity. In preterm complicated pregnancies, an ultrasound-diagnosed Grade III placenta may still be associated with hyaline membrane disease.

Detection of intrauterine growth retardation: a new use for sonographic placental grading

Intrauterine growth retardation (IUGR) is a major source of perinatal death and long-term neurobehavioral morbidity, but its diagnosis antenatally remains difficult. Advanced placental maturity (Grade III), as determined on ultrasound examination, has previously been reported to be a marker of term gestation. In this study of 109 pregnancies which resulted in the birth of infants weighing less than or equal to 2,700 gm, the hypothesis that a Grade III placenta, according to Grannum's classification, can differentiate small-for-gestational age (SGA) infants from small non-SGA infants was tested. Of the study patients, 44 had Grade III placentas and 65 had non-Grade III (0, I, II) placentas within 1 week of delivery. The presence of a Grade III placenta was followed by the delivery of a SGA infant 59% of the time, and 62% of the SGA infants could be correctly identified (p less than 0.001). The association of a Grade III placenta and SGA birth was maintained in patients at less than or equal to 34 weeks of gestation--Grade III placenta was significantly related to the delivery of SGA infants with a true positive rate of 62% and a sensitivity of 66% (p less than 0.008). These results were consistent with the concept that for small fetuses documentation of "maturity" can be used to discriminate those with IUGR from those without this problem. Furthermore, placental "maturation," as detected sonographically, appears to be accelerated in association with IUGR, consistent with the anatomic concept of premature placental senescence. Thus, in situations in which the fetus is known to be small, sonographic grading of the placenta may be helpful in detecting IUGR.

Second-trimester placental changes associated with elevated maternal serum alpha-fetoprotein

Measuring maternal serum alpha-fetoprotein (AFP) levels in the second trimester is an effective screening test for identifying pregnancies at increased risk for neural tube defects. In the absence of a neural tube defect there are many nonpathologic and pathologic causes for elevated AFP including underestimated gestational age, twin gestation, impending fetal death, and rare fetal malformations. In this series, intraplacental sonolucent spaces were detected in a significant percentage of second trimester pregnancies with elevated serum AFP in the absence of any other cause for the elevation. It is postulated that these cystic spaces are a conduit for the transfer of fetal blood into the maternal circulation, thus accounting for the nonpathologic AFP elevation in the maternal serum.

Changes in placental ultrasonic appearance. II. Pathologic significance of Grade III placental changes

Changes in placental texture and structure on ultrasonic examination have been suggested as correlating to advancing fetal pulmonary maturity. The association of preterm appearance of Grade III changes in the placenta in the complicated pregnancy suggests that these changes are associated with a decrease in placental function and premature senescence of the placenta. Placentas were routinely graded on all obstetric examinations performed during a 1-year period of time. Those pregnancies in which Grade III changes in the placenta prior to term were reviewed. A high incidence (78%) of perinatal problems were found in association with preterm appearance of Grade III changes. Perinatal complications included maternal hypertensive disorders, intrauterine growth retardation, abruptio placentae, and fetal distress in labor. The high incidence of these disorders in preterm pregnancies with Grade III changes in the placenta suggests that the sonographic changes found reflect placental dysfunction or senescence rather than normal maturational development. The appearance of Grade III changes in the placenta in the preterm pregnancy is suggested as a predictive indicator of potential perinatal problems in late pregnancy.

The correlation of ultrasonic placental grading and fetal pulmonary maturation in five hundred sixty-three pregnancies

In a previous study, it was suggested that the presence of a grade III placenta correlates 100% with a mature lecithin/sphingomyelin (L/S) ratio and may replace amniocentesis in confirming fetal lung maturity. In this study that hypothesis was tested in 563 pregnancies. All patients underwent amniocentesis and simultaneously had placental grading. The correlations of placental grade with an L/S ration greater than or equal to 2 were: grade 0, 17%; grade I, 68%; grade II, 91%. The correlations of placental grade with the presence of phosphatidylglycerol (PG) were: grade 0, 17; grade 1, 41%; grade II, 79%; grade II, 75%. The false positive rates associated with grade III placenta were, therefore, 7% for mature L/S ratio and 25% for PG present: when combined with a biparietal diameter greater than or equal to 9.0 cm, a grade III placenta incorrectly predicted lung maturity in 8.5%. We conclude that placental grading is not accurate enough to replace amniocentesis as the standard test of fetal pulmonary maturity.

Real-time ultrasound of the placenta in assessment of fetal pulmonic maturity

The use of ultrasound is a noninvasive method of assessing fetal maturity. However, in order for it to be a substitute for amniocentesis, a high degree of accuracy is required. Static ultrasound examination of placental development has revealed certain patterns of maturity which have suggested to be predictors of fetal pulmonary maturity. This study analyzes 100 patients near term for the accuracy of placental grade in predicting pulmonary maturity when measured by the lecithin/sphingomyelin ratio and by clinical development of the respiratory distress syndrome in the neonate. A mature placental grade (Grade III) determined by real-time sonography corresponded to fetal lung maturity in all cases (n = 15). Placental grade as determined by this methodology appeared to be an accurate predictor of fetal maturity in the population examined.

The ultrasonic changes in the maturing placenta and their relation to fetal pulmonic maturity

A practical classification of placental maturity changes has been developed based on a review of multiple ultrasound evaluations of placental texture over a 4 year period. This classification grades placentas from 0 to 3 according to specific ultrasonic findings at the basal and chorionic plates as well as within the substance of the organ itself. The placentas of 129 patients were graded according to this system at the time of ultrasound evaluation. Eighty-six patients had placentas classified as Grade 1 or greater and all of these had lecithin-sphingomyelin (L/S) ratio determinations performed. Mature L/S ratios (2.0) were found in 68% of Grade I (21/31), 88% of Grade II (28/32), and 100% of Grade III placentas (23/23). These results suggest a correlation between maturational changes of the placenta as seen by ultrasound and fetal pulmonic maturity as indicated by L/S ratio.

Distribution of the bulk of the normal placenta. Review and classification of 800 cases by ultrasonography

A series of 800 ultrasonographic placentographies is reviewed and categorized by the location of the main bulk of the placenta. It represents, to our knowledge, the first such study of the undisturbed placenta and demonstrates a remarkably even distribution with frequent overlapping of more than one uterine sector. A simple form of categorization is presented and the clinical implications and value of ultrasonography are underscored.