Evaluation of fetal kidney growth using ultrasound: A systematic review

The thrifty phenotype hypothesis: The association between ultrasound and Doppler studies in fetal growth restriction and the development of adult disease

Barker pioneered the idea that the epidemic of coronary heart disease in Western countries in the 20th century, which paradoxically coincided with improved standards of living and nutrition, has its origin in fetal life. Indeed, there is substantial evidence associating low birthweight because of fetal growth restriction with an increased risk of vascular disease in later adult life. These conclusions led to the second part of the Barker hypothesis, the thrifty phenotype, in which adaptation to undernutrition in fetal life leads to permanent metabolic and endocrine changes. Such changes are beneficial if the undernutrition persists after birth but may predispose the individual to obesity and impaired glucose tolerance if conditions improve. The hypothesis assumes that a poor nutrient supply during a critical period of in utero life may "program" a permanent structural or functional change in the fetus, thereby altering the distribution of cell types, gene expression, or both. The fetus, in response to placental undernutrition and to maintain sufficient vascular supply to the brain, decreases resistance to blood flow in the middle cerebral artery. Simultaneously, because of the limited blood supply to the fetus, the arterial redistribution process is accompanied by increased resistance to flow to other fetal vital organs, such as the heart, kidneys, liver, and pancreas. It may explain why individuals exposed to ischemic changes in utero develop dyslipidemia, lower nephron number, and impaired glucose tolerance, all factors contributing to metabolic syndrome later in life. Nevertheless, support for the hypotheses comes mainly from studies in rodents and retrospective epidemiologic studies. This review focused on ultrasound and Doppler studies of human fetal growth restriction in several fetal organs: the placenta, fetal circulation, brain, heart, kidneys, adrenal glands, liver, and pancreas. Support for the hypothesis was provided by animal studies involving conditions that create fetuses with growth restriction with effects on various fetal organs and by human studies that correlate impaired fetal circulation with the in utero development and function of fetal organs.

Measurement of the Brain Volume/Liver Volume Ratio by Three-Dimensional MRI in Appropriate-for-Gestational Age Fetuses and Those With Fetal Growth Restriction

BACKGROUND

Fetal growth restriction (FGR) is associated with a high fetal brain volume/liver volume (FBV/FLV) ratio. Ultrasound may not always be reliable, which has prompted further investigation of MRI techniques.

PURPOSE

To determine the relationship between FBV/FLV ratio, as measured by MRI, and gestational age (GA) in normal fetuses and those with FGR.

STUDY TYPE

Retrospective.

POPULATION

One hundred and forty seven singleton pregnancies including 105 appropriate-for-gestational age (AGA) fetuses and 42 FGR fetuses.

FIELD STRENGTH/SEQUENCE

Three-dimensional fast imaging employing steady-state acquisition at 1.5 T.

ASSESSMENT

The FBV and FLV were measured by three radiologists. The inter- and intraobserver agreements, the correlation between FBV/FLV ratio, and advancing GA were evaluated; the diagnostic value of FBV/FLV ratio was evaluated and compared with head circumference/abdominal circumference (HC/AC) ratio measured by ultrasound.

STATISTICAL TESTS

Intraclass correlation coefficient (ICC) was used to determine inter- and intraobserver agreements. Regression analysis was used to assess the correlation between FBV/FLV ratio and advancing GA. The diagnostic value of the FBV/FLV ratio was examined by the area under the receiver operating characteristic (ROC) curve.

RESULTS

The inter- and intraobserver agreements were excellent with an interobserver ICC of 0.984 and intra-observer ICCs of 0.989, 0.994, and 0.995. The FBV/FLV ratio in AGA fetuses decreased significantly with advancing GA (Pearson correlation coefficient = -0.844). The FBV/FLV ratio in FGR fetuses was significantly higher than that in AGA fetuses. To identify fetuses at high risk for FGR using the FBV/FLV ratio, the area under the ROC curve was 0.978, with an optimal cut-off value of 4.10. The sensitivity of FBV/FLV ratio in identifying FGR was significantly higher than that of HC/AC ratio (0.929 vs. 0.529).

DATA CONCLUSION

An inverse correlation exists between FBV/FLV ratio and advancing GA in normal fetuses. A high FBV/FLV ratio may be used to ascertain fetuses at high risk for FGR.

LEVEL OF EVIDENCE

3 Technical Efficacy Stage: 3.

The Long-Term Effect of Preterm Birth on Renal Function: A Meta-Analysis

The preterm-born adult population is ever increasing following improved survival rates of premature births. We conducted a meta-analysis to investigate long-term effects of preterm birth on renal function in preterm-born survivors. We searched PubMed and EMBASE to identify studies that compared renal function in preterm-born survivors and full-term-born controls, published until 2 February 2019. A random effects model with standardized mean difference (SMD) was used for meta-analyses. Heterogeneity of the studies was evaluated using Higgin’s I² statistics. Risk of bias was assessed using the Newcastle–Ottawa quality assessment scale. Of a total of 24,388 articles screened, 27 articles were finally included. Compared to full-term-born controls, glomerular filtration rate and effective renal plasma flow were significantly decreased in preterm survivors (SMD −0.54, 95% confidence interval (CI), −0.85 to −0.22, p = 0.0008; SMD −0.39, 95% CI, −0.74 to −0.04, p = 0.03, respectively). Length and volume of the kidneys were significantly decreased in the preterm group compared to the full-term controls (SMD −0.73, 95% CI, −1.04 to −0.41, p < 0.001; SMD −0.82, 95% CI, −1.05 to −0.60, p < 0.001, respectively). However, serum levels of blood urea nitrogen, creatinine, and cystatin C showed no significant difference. The urine microalbumin to creatinine ratio was significantly increased in the preterm group. Both systolic and diastolic blood pressures were also significantly elevated in the preterm group, although the plasma renin level did not differ. This meta-analysis demonstrates that preterm-born survivors may be subject to decreased glomerular filtration, increased albuminuria, decreased kidney size and volume, and hypertension even though their laboratory results may not yet deteriorate.

Gestational echobiometry in brachycephalic bitches using high-definition ultrasonography

ABSTRACT: The objective of the present study was to obtain echobiometric values for the most important canine maternal-fetal tissues using high-definition ultrasonography (HDUS) trying to update the formulas for predicting gestational age. Twelve healthy bitches of brachycephalic breeds weighing 7-13kg and aged one to four years were included. The fetuses were analyzed every day using conventional and high-definition ultrasonography from the eighth day after artificial insemination until the day of delivery, using the ACUSON S2000/SIEMENS ultrasound equipment and specific software. Embryonic and fetal structures; diameter of the embryonic vesicle; length of the embryo; biparietal diameter, abdominal length and kidney height; length of the femur, humerus, scapula, radius, and tibia; thickening of the stomach wall; adrenal length; and cardiac size were measured. These variables were correlated with gestational and adjusted tested according to regression models. The results obtained (P<0.001) for: lateral diameter of the gestational sac (R2=81.8%); length of the embryo (R2=85.7%); biparietal (R2=99.1%) and abdominal diameter (R2=97.2%); thickness of the gastric wall (R2=86.9%); length of the femur (R2=96.6%), radius (R2=97.5%), humerus (R2=96.5%), scapula (R2=95.8%) and tibia (R2=97.3%); kidney length (R2=95.8%) and height (R2=96.0%); adrenal length (R2=89.6%); heart length (R2=93.0%) and height (R2=91.5%) of the canine fetuses showed significant correlation with gestational days. This allowed monitoring fetal growth and estimation of age with high accuracy in different gestational periods.

[Genital abnormalities: Contextualization of a neglected area in prenatal diagnosis]

OBJECTIVE

To reflect on how the area of genital abnormalities has fallen behind in prenatal diagnosis.

METHODS

Based on the thesis that prenatal diagnosis of genital abnormalities has scarcely developed, a comparison with other areas of prenatal diagnosis and with its postnatal counterpart is presented; different explanations for this situation are examined; and a reflection is presented on ways to expand this field of knowledge.

CONCLUSIONS

Compared to other disciplines, prenatal diagnosis of genital abnormalities finds itself lagging behind in terms of diagnostic tools, management protocols and scientific literature. Potential causes include a perception of low prevalence and limited importance, or exploration challenges. Integration of current knowledge, together with the acquisition of the appropriate tools and translation to clinical medicine, would be a way to make this discipline stronger.

Fetal kidney charts of a novel measurement of the renal parenchymal thickness to evaluate fetal kidney growth and potential function

OBJECTIVE

The objective of this study was to develop new standard growth charts for fetal renal parenchymal thickness, length, and volume to define normal ranges for use in clinical practice and to assess the reliability of these measurements.

METHODS

This was a prospective, longitudinal study of 72 low-risk singleton pregnancies undergoing serial ultrasound examinations at least every four weeks. Multiple renal measurements were performed on both kidneys at each scan. The renal parenchymal thickness was measured in the mid-sagittal plane. Standard charts were developed and the intra and interobserver reliability for the renal measurements was analysed.

RESULTS

Standard charts were developed for fetal renal parenchymal thickness, length, and volume.

CONCLUSION

We present novel charts, which demonstrate the growth of the fetal renal parenchyma during pregnancy. They will be useful in clinical practice to identify any alterations from these normal ranges, which may be an important criterion for assisting prenatal diagnosis of renal pathologies and future studies in the prediction of kidney function.

Can measurement of the foetal renal parenchymal thickness with ultrasound be used as an indirect measure of nephron number?

Chronic kidney disease continues to be under recognised and is associated with a significant global health burden and costs. An adverse intrauterine environment may result in a depleted nephron number and an increased risk of chronic kidney disease. Antenatal ultrasound was used to measure the foetal renal parenchymal thickness (RPT), as a novel method to estimate nephron number. Foetal renal artery blood flow was also assessed. This prospective, longitudinal study evaluated the foetal kidneys of 102 appropriately grown and 30 foetal growth-restricted foetuses between 20 and 37 weeks gestational age (GA) to provide vital knowledge on the influences foetal growth restriction has on the developing kidneys. The foetal RPT and renal artery blood flow were measured at least every 4 weeks using ultrasound. The RPT was found to be significantly thinner in growth-restricted foetuses compared to appropriately grown foetuses [likelihood ratio (LR) = 21.06, P ≤ 0.0001] and the difference increases with GA. In foetuses with the same head circumference, a growth-restricted foetus was more likely to have a thinner parenchyma than an appropriately grown foetus (LR = 8.9, P = 0.0028), supporting the principle that growth-restricted foetuses preferentially shunt blood towards the brain. No significant difference was seen in the renal arteries between appropriately grown and growth-restricted foetuses. Measurement of the RPT appears to be a more sensitive measure than current methods. It has the potential to identify infants with a possible reduced nephron endowment allowing for monitoring and interventions to be focused on individuals at a higher risk of developing future hypertension and chronic kidney disease.

The Effect of Preterm Birth on Renal Development and Renal Health Outcome

Preterm birth is associated with adverse renal health outcomes including hypertension, chronic kidney disease, and an increased rate of progression to end-stage renal failure. This review explores the antenatal, perinatal, and postnatal factors that affect the functional nephron mass of an individual and contribute to long-term kidney outcome. Health-care professionals have opportunities to increase their awareness of the risks to kidney health in this population. Optimizing maternal health around the time of conception and during pregnancy, providing kidney-focused supportive care in the NICU during postnatal nephrogenesis, and avoiding accelerating nephron loss throughout life may all contribute to improved long-term outcomes. There is a need for ongoing research into the long-term kidney outcomes of preterm survivors in mid-to-late adulthood as well as a need for further research into interventions that may improve ex utero nephrogenesis.

The Relationship between the Fetal Volume-Corrected Renal Artery Pulsatility Index and Amniotic Fluid Volume

INTRODUCTION

To evaluate if the volume-corrected renal artery pulsatility index (vcRA-PI) is more closely related to the amniotic fluid level than the uncorrected or the gestational age (GA)-adjusted RA-PI.

METHODS

RA-PI and kidney volume were measured in low- and high-risk pregnancies at 17-38 weeks. Fetal anomalies associated with nonrenal causes of abnormal amniotic fluid volume were excluded. The vcRA-PI was calculated by dividing the RA-PI by the renal volume. The RA-PI was adjusted for GA, to obtain the GA-adjusted RA-PI. The uncorrected, GA-adjusted, and the vcRA-PI were related to the amniotic fluid level using nonparametric tests and receiver operating characteristic (ROC) curve analyses.

RESULTS

146 examinations from 59 pregnancies were reviewed. Of these, 16 had oligo- and 15 had polyhydramnios. A higher vcRA-PI was associated with oligohydramnios (OR 2.54, 95% CI 1.67-3.86, p < 0.001), while the uncorrected RA-PI and GA-adjusted RA-PI were not able to predict oligohydramnios. ROC curve analysis showed a high predictive accuracy of the vcRA-PI for oligohydramnios (AUC 0.84, 95% CI 0.72-0.94). On the other hand, the uncorrected RA-PI and GA-adjusted RA-PI significantly predicted polyhydramnios (p = 0.04 and 0.02, respectively), while the vcRA-PI did not.

CONCLUSION

The vcRA-PI is superior to the uncorrected and the GA-adjusted RA-PI in predicting oligohydramnios.

The renal parenchyma-evaluation of a novel ultrasound measurement to assess fetal renal development: protocol for an observational longitudinal study

INTRODUCTION

Disorders of fetal growth, such as intrauterine growth restriction (IUGR) and large for gestational age (LGA), have been found to have a profound effect on the development of the fetal kidney. Abnormal kidney development is associated with hypertension and chronic kidney disease later in life. This study will use a novel ultrasound measurement to assess the renal parenchymal growth and kidney arterial blood flow in the fetus to evaluate the development of the fetal kidneys and provide an indirect estimate of nephron number. Measurements in normally grown, IUGR and LGA fetuses will be compared to determine if changes in renal parenchymal growth can be detected in utero.

METHODS AND ANALYSIS

This longitudinal, prospective, observational study will be conducted over 12 months in the Ultrasound Department of the Townsville Hospital, Australia. The study will compare fetal renal parenchymal thickness (RPT) and renal artery Doppler flow between IUGR fetuses and appropriately grown fetuses, and LGA fetuses and appropriately grown fetuses between 16 and 40 weeks. The fetal RPT to renal volume ratio will also be compared, and correlations between RPT, renal parenchymal echogenicity, fetal Doppler indices and amniotic fluid levels will be analysed.

ETHICS AND DISSEMINATION

This study was approved by the Townsville Health District Human Research Ethics Committee. The study results will form part of a thesis and will be published in peer-reviewed journals and disseminated at international conferences.