Ultrasonic assessment of fetal kidney function in normal and complicated pregnancies

Quantification of Fetal Renal Function Using Fetal Urine Production Rate and Its Reflection on the Amniotic and Fetal Creatinine Levels During Pregnancy

Adequate prediction of fetal exposure of drugs excreted by the kidney requires the incorporation of time-varying renal function parameters into a pharmacokinetic model. Published data on measurements of fetal urinary production rate (FUPR) and creatinine at various gestational ages were collected and integrated for prediction of the fetal glomerular filtration rate (GFR). The predicted GFR values were then compared to neonatal values recorded at birth. Collected data for FUPR across different gestational ages using both 3D (N = 517) and 2D (N = 845) ultrasound methods showed that 2D techniques yield significantly lower estimates of FUPR than 3D (p < 0.0001). A power law function was shown to best capture the change in FUPR with fetal age (FA) for both 2D ( F U P R 2 D ( m L min ) = 0 . 000169     FA 2 . 19 ); and 3D ( F U P R 3 D   ( m L min ) =   3 . 21 × 1 0 - 7   FA 4 . 21 ) data. The predicted FUPR based on the observed 3D data was shown to be strongly linearly related (R ² = 0.95) to measured values of amniotic creatinine concentration (N = 664). The FUPR_3D data together with creatinine levels in the fetal urine and serum resulted in median predicted fetal GFR values of 0.47, 1.2, 2.5, and 4.9 ml/min at 23, 28, 33, and 38 weeks of fetal age (50% CV), respectively. These values are in good agreement with neonatal values observed immediately at birth. The derived FUPR and creatinine functions can be utilized to assess fetal renal maturation and predict fetal renal clearance.

Clinical consequences of developmental programming of low nephron number

Nephron number in humans varies up to 13-fold, likely reflecting the impact of multiple factors on kidney development, including inherited body size and ethnicity, as well as maternal health and nutrition, fetal exposure to gestational diabetes or preeclampsia and other environmental factors, which may potentially be modifiable. Such conditions predispose to low or high offspring birth weight, growth restriction or preterm birth, which have all been associated with increased risks of higher blood pressures and/or kidney dysfunction in later life. Low birth weight, preterm birth, and intrauterine growth restriction are associated with reduced nephron numbers. Humans with hypertension and chronic kidney disease tend to have fewer nephrons than their counterparts with normal blood pressures or kidney function. A developmentally programmed reduction in nephron number therefore enhances an individual's susceptibility to hypertension and kidney disease in later life. A low nephron number at birth may not lead to kidney dysfunction alone except when severe, but in the face of superimposed acute or chronic kidney injury, a kidney endowed with fewer nephrons may be less able to adapt, and overt kidney disease may develop. Given that millions of babies are born either too small, too big or too soon each year, the population impact of altered renal programming is likely to be significant. Many gestational exposures are modifiable, therefore urgent attention is required to implement public health measures to optimize maternal, fetal, and child health, to prevent or mitigate the consequences of developmental programming, to improve the health future generations.

Usefulness of fetal urine production measurement for prediction of perinatal outcomes in uteroplacental insufficiency

OBJECTIVES

To evaluate whether fetal urine production measurement is useful for predicting adverse outcomes in patients with uteroplacental insufficiency.

METHODS

We enrolled patients with uteroplacental insufficiency at 24 to 40 weeks' gestation and normal pregnancies matched for gestational age and divided them into 3 groups according to perinatal outcomes: group 1 (n = 141), a control group of normal pregnancies; group 2 (n = 29), uteroplacental insufficiency without adverse outcomes; and group 3 (n = 18), uteroplacental insufficiency with adverse outcomes. An adverse outcome was defined as 1 or more of the following: (1) cesarean delivery because of fetal distress; (2) admission to the neonatal intensive care unit; (3) cord arterial pH less than 7.15 at birth; and (4) low 5-minute Apgar score (<7). The fetal urine production rate was obtained by serial bladder volume measurement using virtual organ computer-aided analysis. For bladder volume determination, we scanned the bladder in the 3-dimensional mode and defined the bladder surface contour in the reference plane, repeating the rotation of the reference plane with an angle of 30° and determining the surface contour on each plane. Statistical methods, including the Mann-Whitney U test, Fisher exact test, χ(2) test, and Kruskal-Wallis analysis of variance, were used.

RESULTS

Group 3 had a lower mean fetal urine production rate than groups 1 and 2, whereas the urine production rate was not different between groups 1 and 2 (group 1, 49.0 mL/h; group 2, 59.4 mL/h; group 3, 20.7 mL/h; P < .001 between groups 1 and 3 and between groups 2 and 3). This difference between groups 2 and 3 remained significant after adjusting for the amniotic fluid index, umbilical artery Doppler pulsatility index, and presence of fetal growth restriction.

CONCLUSIONS

Uteroplacental insufficiency cases with adverse perinatal outcomes had a lower fetal urine production rate than those without adverse outcomes. This difference might be used to predict adverse perinatal outcomes in uteroplacental insufficiency.

Measuring the rate of fetal urine production using three-dimensional ultrasound during normal pregnancy and pregnancy-associated diabetes

OBJECTIVE

To establish a nomogram of fetal urine production according to gestational age as a predictor for fetal well-being in normal and diabetic women.

STUDY DESIGN

Prospective observational study included 180 pregnant women classified into two groups: Group I (120 women) without any medical complications and Group II (60 women) with gestational diabetes mellitus (GDM). The fetal bladder is measured by the virtual organ computer-aided analysis VOCAL 3D ultrasound scanner.

RESULTS

There was a significant positive correlation between gestational age and fetal urine production rate (UPR) (the mean UPR rate in normal pregnancy at 25, 30, 35, 40 weeks were 12.3, 14.38, 56.13 and 90.73 ml/h, respectively). There was no significant difference regarding UPR ml/h between women with normal pregnancy and those with controlled GDM (p = 0.9). There was a statistically significant difference regarding UPR ml/h between women with normal pregnancy and those with uncontrolled GDM (p = 0.012) and a statistically significant difference between women with controlled GDM and those with uncontrolled GDM (p = 0.03).

CONCLUSION

Fetal UPR is considered to be more reliable as an assessment method for fetal well-being and shows significant increase in patients with uncontrolled gestational DM.

Measurement of fetal urine production to differentiate causes of increased amniotic fluid volume

OBJECTIVES

In polyhydramnios, amniotic fluid (AF) volume can be increased not only as a result of increased fetal urine production, but also due to several other factors, including impairment of both fetal swallowing and gastrointestinal (GI) absorption of AF. Our aim was to evaluate whether measurement of the fetal urine production rate (UPR) can be used to differentiate the causes of increased AF volume.

METHODS

This cross-sectional study included 54 pregnant women with an increased amniotic fluid index (AFI), defined as AFI > or = 18 cm, divided into two groups according to the presence of fetal anomalies that are associated with impairment of fetal swallowing or decreased GI absorption of AF (Group 1, n = 14) or the absence of fetal anomalies (Group 2, n = 40). The control group included 96 normal pregnancies with normal AFI (8 < or = AFI < 18 cm) (Group 3). Fetal UPR was obtained by serial bladder volume measurements (two to four times, with a median interval of 5 min between each) using the rotational method of Virtual Organ Computer-aided AnaLysis (VOCAL()) with three-dimensional ultrasound. To adjust for fetal weight (Wt) and gestational age (GA), UPR_Wt and UPR_SD were calculated using the following formulae: UPR_Wt = measured UPR/estimated fetal weight and UPR_SD = (measured UPR - mean UPR for each GA)/SD of UPR for each GA.

RESULTS

The AFI was increased significantly in Groups 1 and 2 compared with Group 3. However, the median fetal UPR in Group 1 did not differ from that of Group 3, in contrast to the higher median fetal UPR in Group 2 compared with Groups 1 and 3; this difference remained significant after adjusting for GA and estimated fetal weight in terms of UPR_SD and UPR_Wt. In Groups 2 and 3, AFI and UPR had a positive correlation in terms of UPR, UPR_SD and UPR_Wt.

CONCLUSIONS

Our findings that fetal UPR is significantly increased in cases with increased AFI without fetal anomalies, but not in those with increased AFI and fetal anomalies involving decreased GI absorption of AF, might be used to differentiate causes of increased AF volume. In the absence of fetal anomalies, AFI and fetal UPR correlate positively.

Three-dimensional power Doppler analysis of cerebral circulation in normal and growth-restricted fetuses

The objective of the present study was to evaluate fetal cerebral circulation by using three-dimensional (3D) power Doppler ultrasound in normal and growth-restricted fetuses. A total of 100 normal grown fetuses were compared with other 25 with growth restriction (FGR). Three-dimensional power Doppler ultrasound was used to assess fetal cerebral 3D vascular indices: vascularization index, flow index (FI), and vascularization flow index (VFI). Both FI and VFI correlated positively with gestational age. On average, all the 3D vascular indices were increased in fetuses with FGR. The proportion of fetuses detected as having hemodynamic redistribution was higher when using 3D power Doppler indices than by means of the middle cerebral artery pulsatility index (52% versus 20%, P=0.002). In conclusion, two of the three indices increased during gestation. All the fetal cerebral 3D vascular indices are increased in fetuses with FGR. In these fetuses, there were more cases suggesting hemodynamic redistribution than expected by conventional Doppler studies.

Oligohydramnios and associated fetal complications

During intrauterine life the fetus is bathed in amniotic fluid which provides a low resistance space for free movement and a buffer against external trauma. This fluid is produced in early pregnancy largely as a maternal dialysate, then as a fetal transudate. Fetal urine is the most important source of amniotic fluid after 16 weeks gestation. The control of amniotic fluid is complex and poorly understood; it arises from secondary partitioning of water within the fetoplacental extracellular space and reflects fetal fluid balance.

Pathophysiology of amniotic fluid volume homoeostasis

Human and ovine fetuses produce and absorb prodigious amounts of water and electrolytes daily. As will be described, fetal fluid exchange approximates to 300–400ml/kg per day near term. On a per kilogram basis, this is equivalent to an adult ingesting and secreting 15–20 litres per day. Upon delivery, the newborn rapidly adjusts to a much reduced rate of fluid exchange. In this respect, the fetus resembles an amphibian during development: an aquatic phase of in utero gestation and a comparatively arid state following delivery. Although the amphibian-like pattern of development may be partly an example of ‘ontogeny recapitulates phylogeny’, the remarkable volume of fetal fluid exchange suggests an important physiological role for amniotic fluid.

Perinatal bile acid metabolism: bile acid analysis of meconium of preterm and full-term infants

BACKGROUND

Our purpose was to evaluate the metabolism of bile acids in the fetus by analyzing the bile acid composition of meconium of preterm (less than 30 weeks' gestational age) and full-term infants and comparing the results with the bile acid composition of feces of preterm and full-term infants 6 days after delivery.

METHODS

The concentrations of individual bile acids were determined by gas chromatography-mass spectrometry after solvolysis and hydrolysis of bile acid conjugates.

RESULTS

In meconium, the main bile acids were chenodeoxycholic and hyocholic acids. The main bile acid of feces from preterm infants at 6 days of age was the same as that of meconium. We also detected large amounts of secondary bile acids, especially deoxycholic acid and ursodeoxycholic acid. The ratio of cholic acid relative to chenodeoxycholic acid in meconium of preterm and full-term infants and in feces of preterm infants was less than 1, 0.36, 0.55, and 0.55, respectively. The percentage of chenodeoxycholic acid relative to total bile acids in meconium of preterm (P < 0.05) and full-term (P < 0.01) infants was significantly higher than that in feces of 6-day-old full-term infants.

CONCLUSIONS

More than half of the main pathway, at least, for bile acid synthesis in preterm infants may be the acidic pathway until the infants reach about 7 days of age.

Measurement of fetal urine production by three-dimensional ultrasonography in normal pregnancy

OBJECTIVES

Measurement of fetal urine production may provide a means of evaluating amniotic fluid volume, which is difficult to measure directly, and predicting fetal hypoxia. Although there have been some reports on fetal urine production, most of these have used two-dimensional (2D) ultrasonography to measure bladder volume. Three-dimensional (3D) ultrasonography is, however, known to be superior to 2D ultrasonography in some organ volume measurements. Thus, we undertook this study to measure bladder volumes using 3D ultrasonography and to establish a nomogram of fetal urine production rate (UPR) according to gestational age (GA).

METHODS

One hundred and fifty-four women with a normal singleton pregnancy at 24 to 40 weeks' gestation were enrolled in this cross-sectional study. The women had no medical or obstetric complications affecting amniotic fluid volume. Fetal bladder volume was measured using 3D ultrasound imaging and Virtual Organ Computer-aided AnaLysis (VOCAL) with a rotational angle of 30 degrees and manual surface tracing technique. Bladder volume was measured two or three times within a 5-10-min interval and fetal UPR was calculated from serial measurements. When measurements were performed more than twice, we used the mean rate of calculated UPRs. UPR was then plotted against GA to establish the nomogram.

RESULTS

Fetal UPR increased with GA from a median value of 7.3 mL/h at 24 weeks' gestation to 71.4 mL/h at term, and could be calculated from GA using the formula: Ln(UPR) = - 6.29582 + (0.43924 x GA) + (0.000432 x GA2), r2 = 0.63, P = 0.0046. Growth percentiles of UPR according to age are presented.

CONCLUSIONS

Fetal UPR can be easily measured by 3D ultrasound assessment of bladder volume. This modality may be a promising alternative to conventional methods of amniotic fluid volume measurement such as amniotic fluid index and single deepest pocket, and might be an alternative option for predicting fetal hypoxia.

Three-dimensional ultrasound fetal urinary bladder volume measurement: reliability of rotational (VOCALTM) technique using different steps of rotation

OBJECTIVE

The aim of the study was to investigate the inter- and intraobserver reliability in measuring the fetal bladder volume by 3d ultrasound imaging by VOCAL. In addition a comparison of 15 degrees and 30 degrees rotation steps calculation had been performed.

METHODS

Measurements (n = 240) of FB volume were performed in 30 low-risk patients with gestation times ranging from 22 to 39 weeks by two independent observers blind to each other. All fetuses were examined and no ultrasound detectable malformation was found. The volume for each FB was measured twice by the observers who used the Virtual Organ Computed-aided Analysis (VOCAL) technique. Distinct sets of 12 and 6 planes were obtained after sequential rotations of 15 degrees and 30 degrees, respectively. The internal contour of fetal bladder was determined manually and carefully as to exclude adjacent structures from volume calculation. Wilcoxon signed-rank test was used for the comparison of paired samples in the cases of replication within and between observers. Spearman's rank correlation was used to study the relationship among angles. Bland and Altman's graphical approach was used to investigate the agreement between observers.

RESULTS

Both techniques were shown to be highly reliable. No significant difference was found between the measurements of FB volume with the VOCAL technique by varying either the steps of rotation or the observers.

CONCLUSION

Excellent correlations were found for both observers in the use of rotation angles of 15 degrees and 30 degrees . Since a significantly faster evaluation was obtained by using a 30 degrees rotation step it must be preferred to assess the FB volume. Our results show that the VOCAL technique, with a plane rotation of 30 degrees , can be used in a simple way to estimate fetal urine production.

Amniotic fluid index and birth weight: is there a relationship in diabetics with poor glycemic control?

OBJECTIVE

This study was undertaken to evaluate if the previously demonstrated relationship between macrosomia (> 4000 g) and polyhydramnios (> 25 cm) is linear across birth weights (BW) in diabetic patients with poor glycemic control.

STUDY DESIGN

Using a prospectively collected database of patients undergoing amniocentesis for fetal lung maturity for various indications with amniotic fluid index (AFI) obtained < or = 7 days before delivery and BWs available (n = 69), we computed gestational age (GA) specific AFI and BW centiles using standard tables. BW and AFI centiles were analyzed in diabetic patients with poor glycemic control using linear regression and ANOVA, with P < .05 significant.

RESULTS

In the poorly controlled diabetic population, a linear relationship existed between AFI and BW centiles, with the largest BW centiles having the highest AFI centiles (P < .0001).

CONCLUSION

The previously noted relationship between elevated AFI and BW centiles in the general patient population is linear in diabetic patients with poor glycemic control.

Consequences of Intrauterine Growth Restriction for the Kidney

Low birth weight due to intrauterine growth restriction is associated with various diseases in adulthood, such as hypertension, cardiovascular disease, insulin resistance and end-stage renal disease. The purpose of this review is to describe the effects of intrauterine growth restriction on the kidney. Nephrogenesis requires a fine balance of many factors that can be disturbed by intrauterine growth restriction, leading to a low nephron endowment. The compensatory hyperfiltration in the remaining nephrons results in glomerular and systemic hypertension. Hyperfiltration is attributed to several factors, including the renin-angiotensin system (RAS), insulin-like growth factor (IGF-I) and nitric oxide. Data from human and animal studies are presented, and suggest a faltering IGF-I and an inhibited RAS in intrauterine growth restriction. Hyperfiltration makes the kidney more vulnerable during additional kidney disease, and is associated with glomerular damage and kidney failure in the long run. Animal studies have provided a possible therapy with blockage of the RAS at an early stage in order to prevent the compensatory glomerular hyperfiltration, but this is far from being applicable to humans. Research is needed to further unravel the effect of intrauterine growth restriction on the kidney.

Elevated Aldosterone in Amniotic Fluid and Maternal Blood Has Diagnostic Potential in Pregnancies Complicated with a Fetus of Bartter Syndrome

Pregnancies with fetuses affected with the Bartter syndrome, an autosomal recessive disorder of hyperreninism and hyperaldosteronism, are complicated by early onset of polyhydramnios which results in preterm deliveries. We have assessed biochemical changes in amniotic fluid and the mother's blood with a view to early diagnosis. Aldosterone levels of both amniotic fluid and the mother's blood were found to be increased at 27 weeks of gestation, while electrolyte levels did not differ significantly from those reported earlier for controls. After birth the baby suffered from polyuria with hyponatremia, hypomagnesemia and hypercalciuria which could be controlled by treatment with sodium chloride and magnesium. Elevated aldosterone thus might be a useful marker for early diagnostic purposes.

Hemodynamics of the renal artery and descending aorta in fetuses with renal disease using color Doppler ultrasound--longitudinal comparison to normal fetuses

OBJECTIVE

To examine the hemodynamic values of the renal artery (RA) and descending aorta (DA) in normal fetuses, and to compare these values to those of fetuses with renal disease, thus evaluating the usefulness of hemodynamic analysis for the diagnosis of fetal renal disease.

MATERIALS AND METHODS

We examined 46 normal fetuses and 15 fetuses with renal disease (six cases of polycystic kidney (PCK) and nine cases of hydronephrosis). We measured the maximum systolic velocity (Vmax ) of the RA and DA using color Doppler. Measurements were made five times, from the 20th to the 40th week, in both the control and the renal disease group.

RESULTS

In the fetuses with PCK (Potter's syndrome) that died postpartum from non-functional kidneys, the Vmax of the RA and DA in the 35th week were 13 cm/s and 25.4 cm/s, respectively. In the fetus with PCK (Trisomy 9) that died due to non-functional kidneys in the 34th week, the values were 13.3 cm/s and 29.6 cm/s, respectively. These values were well below those of the normal group: more than 1.5 SD below the mean. In two fetuses from the nine with hydronephrosis that had a unilateral non-functional kidney, the RA did not clearly show identifiable blood flow.

CONCLUSIONS

The V max of the RA and DA in fetuses with renal disease correlates with fetal kidney function, particularly the RA Vmax.Vmax of 1.5 SD below the mean should be the lower normal limit.

Avaliação prospectiva do índice de líquido amniótico em gestações normais e complicadas

OBJETIVO: Analisar, prospectivamente, o índice de líquido amniótico em gestantes de baixo risco que apresentaram ou não complicações da gestação e do período perinatal. MATERIAIS E MÉTODOS: Foi estudado, de modo prospectivo, o índice de líquido amniótico de 45 primigestas sem doenças no momento da inclusão no estudo. O índice foi avaliado em quatro períodos da gestação - 18-20, 24-26, 28-30 e 34-36 semanas - e seus valores foram correlacionados com o surgimento de complicações gestacionais e perinatais, Doppler das artérias uterinas, idade gestacional ao parto, vias de parto e o peso dos recém-nascidos. RESULTADOS: O índice de líquido amniótico não mostrou diferença estatística entre as pacientes com gestações normais e complicadas em nenhum dos quatro períodos estudados. Também não mostrou associação com a idade gestacional ao parto, as vias de parto e o peso dos recém-nascidos. Observou-se que a média do índice de líquido amniótico entre 28-30 semanas é mais elevada (p = 0,004) nas pacientes com incisura bilateral do que nas com Doppler normal. CONCLUSÃO: A avaliação prospectiva do índice de líquido amniótico em gestações de baixo risco parece não ser um bom preditor de complicações gestacionais ou perinatais.

Analysis of renal artery hemodynamics in normal fetuses using the color Doppler method

OBJECTIVE

From analysis of fetal renal artery hemodynamics, we attempted to reveal renal glomerular and tubular function in normal fetuses during pregnancy.

DESIGN

The study included 36 cases of normal fetuses from the 20th to the 40th week of gestation; V(max) (the systolic peak velocity of main renal artery), V(mean) (time averages of trace of peak velocity) blood flow were initially measured between 20 and 24 weeks of gestation and every 4 weeks thereafter. The measurement was performed a total of five times in a longitudinal study. In addition, the blood flow waveform was concurrently examined.

RESULTS

The V(max) was 22.02 +/- 0.50 cm/s at 20-24 weeks of gestation. This standard value (100%) was found to increase for each group as follows: 125.2, 149.1, 156.1, and 181.5%. Furthermore, using 20-24()weeks of gestation as the standard, the V(mean) increased after the 37th week of gestation: 186.7%, respectively. At 20-24 weeks of gestation, the blood flow wave forms consisted of 43.2% type I (only systolic waveforms), and 56.8% type II (both systolic and diastolic waveforms). Type III waveforms (waveforms that extended beyond the diastolic to the next systolic component) were not recognized. In the 33- to 36-week group, 82.6% of the waveforms were type II, and in the 37- to 40-week group, 76.2% of the waveforms were type III.

CONCLUSIONS

The V(max) and V(mean) of the renal artery in normal fetuses exhibit a similar rate increase when 20-24 weeks of gestation is compared to 37-40 weeks of gestation. The blood flow waveforms changed as pregnancy progresses; thus, it was inferred that this finding was related to the development of the renal glomerular and renal tubular function.

The amniotic fluid index in late pregnancy

OBJECTIVE

Our purpose was to examine changes in the amniotic fluid index (AFI) in accurately dated term pregnancies both in relation to gestational age and in relation to the onset of spontaneous labor.

STUDY DESIGN

This was a prospective observational study in 137 women with uneventful term pregnancies, in whom 220 AFI measurements were performed. More than one AFI value was available from 51 individuals.

RESULTS

The AFI did not change significantly between 37 and 42 weeks' gestation, but a significant reduction was seen during the last 11 days before the spontaneous onset of labor (R = -0.37, n = 83, p < 0.001). The AFI (corrected for gestational age) within individuals remained stable over periods of up to 2 weeks. Meconium staining of the amniotic fluid was related to gestational age, but not to the AFI or fetal distress at birth. No significant correlation was found between fetal distress and the AFI, or between fetal distress and the reduction in AFI during the last two measurements before labor.

CONCLUSIONS

The reduction of the AFI in pregnancies progressing beyond term is related to the labor process itself rather than to the exact gestational age.

Intrauterine growth restriction in rats is associated with hypertension and renal dysfunction in adulthood

Epidemiological studies have produced evidence that unfavorable intrauterine environments during fetal life may lead to adverse outcomes in adulthood. We have previously shown that a low-sodium diet, given to pregnant rats over the last week of gestation, results in intrauterine growth restriction (IUGR). We hypothesize that pups born with IUGR are more susceptible to the development of hypertension in adulthood. IUGR fetuses and rats aged 1 wk were characterized for organ growth and renal morphogenesis. The adults (12 wk) were evaluated for weight, systolic blood pressure, activity of the renin-angiotensin-aldosterone system (RAAS), and renal function; hearts and kidneys underwent a histological examination. Brain and cardiac ventricle-to-body ratios were increased in IUGR fetuses compared with age-matched controls, whereas the kidney-to-body ratio was unchanged. Systolic blood pressure was elevated in both IUGR male and female adults. Plasma aldosterone levels were not correlated with increased plasma renin activity. Moreover, urinary sodium was decreased, whereas plasma urea was elevated in both males and females, and creatinine levels were augmented only in females, suggesting a glomerular filtration impairment in IUGR. In our model of IUGR induced by a low-sodium diet given to pregnant rats, high blood pressure, alteration of the RAAS, and renal dysfunction are observed in adult life. Differences observed between male and female adults suggest the importance of gender in outcomes in adulthood after IUGR.

A longitudinal study of amniotic fluid index in normal pregnancy in Nigerian women

OBJECTIVE

To establish normal reference values of amniotic fluid index by week of gestation for normal pregnancies in our population.

METHOD

A longitudinal prospective assessment of amniotic fluid index in healthy pregnant women carrying singleton pregnancies. The subjects were recruited at 20 or 22 weeks of gestation and concluded at 40 or 42 weeks of gestation. The numeral data were analyzed on an IBM Personal System 2 computer with statistical and graphical packages.

RESULT

from a mean of 17.18 cm at 20 weeks gestation, the amniotic fluid index rose progressively to a peak of 20.39 cm at 26 weeks gestation. It then gradually declined to a mean of 8.37 cm at 42 weeks gestation.

CONCLUSION

Gestational age specific values of amniotic fluid index should be used and the 5th and 95th percentiles taken as lower and upper limits of normal, respectively.

Fetal urine production and accuracy when estimating fetal urinary bladder volume

OBJECTIVES

The volume of the fetal urinary bladder can be estimated by measuring bladder diameters on an ultrasound image. The calculated urine production rate might reflect the fetal status in compromised pregnancies. The aim of this study was to assess the fetal urine production rate and the accuracy of measurements of diameters and volumes of the bladder.

DESIGN

Urine production rate and the variability in volume measurement error were assessed by ultrasound examinations of fetal bladder images documented on videotapes. In material comprising 101 longitudinal and 90 transverse bladder images, the variability (SD) in distance measurement error was estimated for the bladder diameters. Using this SD, the variability in volume measurement error in the selected bladder image was also calculated.

RESULTS

The urine production rate for fetuses of 20, 25, 30, 35 and 40 weeks is 4.2, 12.1, 22.7, 36.1 and 52.2 mL/h, respectively. The SD for volume measurement error when selecting bladder images with a volume of 5, 10, 20, 30 and 40 mL is 17.3%, 13.6%, 11.8%, 11.2% and 10.9% of the actual volume, respectively. The corresponding SD when measuring the volume of selected bladder images accounted for 3.7-2.0%.

CONCLUSIONS

The urine production rate presented here is in parity with recent previous reports. We distinguish between different kinds of measurement error. The variability was mostly related to the selection of appropriate bladder image, whereas measurement of the selected bladder image accounted for only a minor part of the resulting variability.

Morphometry of human ovaries in normal and growth-restricted fetuses

According to the fetal origins hypothesis, normal growth and development of abdominal organs is disturbed by intra-uterine growth restriction, leading to diseases later in life. The aims of this study were to investigate the effect of growth restriction on the ovaries of human fetuses and to investigate the dynamics of follicular growth in normal fetuses. We selected 21 normal female fetuses (controls) and seven severely intra-uterine growth-restricted female fetuses (IUGR cases) from all autopsy records over a 10-year period. Ovarian volume was calculated and from histological sections the volume-percentage of follicles in the ovarian cortex, the maximum diameters of individual follicles and the distribution of the follicle classes and oogonia were determined. The volume of the ovaries increased significantly from 0.10 to 0.36 cm3 in the second half of gestation. The mean volume-percentage of ovarian follicles and the mean follicle diameter significantly increased with 0.48% and 0.52 microm per week, respectively. Class B/C (intermediary) follicles (72%) were predominantly present. Class B (primordial) follicles decreased from over 20% to less than 10% and class C (primary) increased from 6 to 19%. Class A (oogonia) were frequently present before 30 gestational weeks, but were rare after that age. For all studied parameters we did not find differences between IUGR cases and controls. Intra-uterine growth restriction does not seem to disturb ovarian development in the human fetus. In the second half of gestation the follicle pool increases by the growth of individual follicles, the transition of follicle to larger classes, and probably by increasing follicle numbers. As most follicles at term were class B/C and C, follicles up to class C are probably part of the resting stock.

Fetal growth retardation as a cause of impaired ovarian development

Low birthweight has been associated with diseases and disorders later in life. It has been suggested that this is caused by the impaired development of abdominal organs, especially in cases of growth retardation. Besides general malnutrition of the fetus, preferential bloodflow to the heart and brain may further deprive organs, such as liver, pancreas and kidney, of nutrients. As a result these organs may not develop properly. Anatomically, the ovary is situated close to the kidney and it is very likely that, similar to the kidney, ovarian development can be negatively affected by intra-uterine growth retardation. Placental insufficiency, which is an important cause of severe intra-uterine growth retardation, was used as a model to investigate this hypothesis. In the present study, the volume percentages of primordial follicles in the ovaries of four severely growth-retarded fetuses of different gestational ages are compared to those of four age-matched controls. It is found that these volume percentage in growth-retarded fetuses were significantly lower than those observed in the age-matched controls. It can be concluded that ovarian development is impaired in intra-uterine growth-retarded fetuses. These findings further suggest that, as a result of the premature loss of follicles, females with low birthweights may encounter fertility problems later in life.

Ultrasound measurement of fetal urine flow

In summary, the measurement of fetal urinary flow remains controversial because the actual volumes of the human fetal bladder are unknown. The volume formula for an ovoid overpredicts fetal bladder volume and has a wide margin of certainty. The best ultrasonographic prediction of bladder volumes were calculated by applying a regression formula to the area of a sagittal sonographic image of the bladder (0.46323 + 1.39394.sagittal area). Calculations of the HFUFR based on the ovoid volume formula may be overestimated by 40%-70%. However, HFUFR estimated by regression of three to six longitudinal bladder area measurements is better with a narrow margin of uncertainty (+/- 35%). This technique affords improved accuracy and is easier and more convenient.

Fetal urine production at different gestational ages: correlation to various compromised fetuses in utero

To reveal which fetal life-threatening diseases significantly contribute to impairment of in-utero urine production and also to determine the gestational age at which time aberrant urine production becomes manifest, we observed 376 compromised fetuses (subject group) at 21-42 weeks' gestation using ultrasonography. A total of 358 uncomplicated fetuses, aged 21-40 weeks, were separately chosen as a control group. Statistical differences in the urine production rate between subject- and control-group fetuses were analysed using the Grubbs-Smirnoff test at corresponding gestational ages. Significant decreases were evident in: bilateral renal agenesis (100%) at 21-23 weeks; bilateral infantile polycystic kidney (100%) at 21-28 weeks; bilateral multicystic kidney disease (100%) at 21-31 weeks; donor fetuses with twin transfusion syndrome (TTS) (100%) at 21-28 weeks; post-term fetuses (100%) at 42 weeks; bilateral hydronephrosis (60%) at 21-38 weeks; non-immunologic hydrops fetalis (42%) at 21-35 weeks; intrauterine growth retardation (41%) at 29-40 weeks; and upper gastrointestinal tract obstruction (36%) at 30-38 weeks. Significant increases were noted in: recipient fetuses with TTS (100%) at 21-28 weeks, and unilateral hydronephrosis (36%) at 27-32 weeks. All indicate that urine production clearly delineates various fetal conditions in utero, in a closely disease-dependent relation to gestational age.

Effect of maternal cocaine abuse on renal arterial flow and urine output of the fetus

OBJECTIVE

Our purpose was to study the short-term effect of maternal cocaine abuse on blood flow of the fetal kidney and the fetal hourly urine output.

STUDY DESIGN

Thirty-three pregnant patients of various gestational ages with a history of cocaine abuse were studied. Patients were included if the urine specimen was positive for cocaine on the day of study. Patients were excluded if the urine specimen was positive for any other vasoactive substances or medications. Color and pulsed wave Doppler studies were used to obtain the flow velocity waveform of the fetal renal artery. The resistance index was calculated from systolic and diastolic values of flow velocity waveforms, Longitudinal, transverse, and anteroposterior diameters of the fetal urinary bladder were measured from transverse and coronal images at their maximum diameters, and the bladder volume was calculated. The hourly urine output of the fetus was measured from the difference in the bladder volume at half-hour intervals. As controls, 110 normal pregnancies between 19 and 40 weeks were similarly studied for normal values. The resistance index of the fetal renal artery and the hourly fetal urine output of the two groups were compared.

RESULTS

The resistance index of the fetal renal artery of normal pregnancies had a negative association with gestational age (p < 0.05). Cocaine-exposed fetuses had a significantly higher resistance index of the renal artery (p < 0.01) than did normal fetuses of corresponding gestational ages. A decrease in the hourly urine output of cocaine-exposed fetuses was observed, compared with normal controls of corresponding gestational ages (p < 0.001).

CONCLUSION

The resistance index values of fetal renal artery and fetal urine output were affected by maternal cocaine abuse.

Amniotic fluid volume reflects recent glycemic status in gestational diabetes mellitus

OBJECTIVE

Our purpose was to determine the association between amniotic fluid volume and recent glucose status in gestational diabetes.

STUDY DESIGN

Serial amniotic fluid index values, mean blood glucose levels, and percent hyperglycemia (> or = 120 mg/dl) 1 day and 1 week before the ultrasonographic examinations were prospectively collected in 399 gestational diabetics. Patients demonstrating at least one amniotic fluid index measurement within the normal range (i.e., 5 cm < amniotic fluid index < or = 20 cm) and at least one elevated measurement (i.e., amniotic fluid index > 20 cm) formed the study group. With each patient serving as her own control, glucose index values preceding normal and elevated amniotic fluid index values were compared.

RESULTS

Significantly higher mean blood glucose values 1 day (114.7 mg/dl vs 102.8 mg/dl, p < 0.01) and 1 week before (111.0 mg/dl vs. 102.0 mg/dl, p < 0.05) were calculated for examinations resulting in elevated amniotic fluid index values compared with normal amniotic fluid index values, respectively. Similarly, significantly higher percents of hyperglycemia 1 day (32% vs 16.5%, p < 0.05) but not 1 week (30.8% vs 21.7%, p > 0.05) before the elevated amniotic fluid index were documented.

CONCLUSION

Amniotic fluid volume reflects recent glycemic status in gestational diabetes mellitus.

Accuracy limits of ultrasonographic estimation of human fetal urinary flow rate

OBJECTIVE

Our purpose was to define the accuracy of currently available methods of ultrasonographically estimating human fetal urinary flow rate in a controlled setting.

STUDY DESIGN

Eleven fetal cadavers were studied in a water bath. Saline solution was incrementally infused into the bladder to simulate a rate of 1 ml/min. Serial fetal bladder volumes were calculated from ultrasonographic measurements by means of the ovoid volume formula (ovoid volume = 4/3.pi.(D1.D2.D3)/8 and ellipse sagittal-area and coronal-area volume formulas that we previously reported (Sagittal-area volume = 0.46323 + 1.39394. Sagittal area and Coronal-area volume = 1.20640 + 1.07603. Coronal area). Fetal urinary flow rate was determined by (1) subtracting the mean of two fetal bladder volumes at the start and end of a simulated 30-minute bladder filling or (2) linear regression of three, four, five, and six fetal bladder volume observations against time. The means of fetal urinary flow rate estimates and errors derived with each method were compared to the actual rate of 1 ml/min by means of the Student t test.

RESULTS

The volume subtraction technique with ovoid volume yielded a fetal urinary flow rate of 1.68 ml/min (95% confidence interval 0.86 to 2.50 ml/min). Similar overprediction of fetal urinary flow rate occurred with regression with ovoid volume (1.45 ml/min, 95% confidence interval 0.61 to 2.29 ml/min). Estimated fetal urinary flow rates (from sagital-area volume and coronal-area volume (0.99 ml/min, 95% confidence interval 0.64 to 1.34 ml/min) were significantly more accurate than those from ovoid volume (p < 0.0001). Regression with 3 (95% confidence interval +/- 40%) or 4 points (95% confidence interval +/- 37%) was marginally less accurate than with 5 (95% confidence interval +/- 36%) or 6 points (95% confidence interval +/- 35%, p = 0.02).

CONCLUSIONS

Ultrasonographic estimates of fetal urinary flow rate based on the ovoid volume formula overestimate the true rate by 40% to 70%. Fetal urinary flow rate calculated by regression of three to six sagittal or coronal bladder area measurements is a better estimate of true rate with a satisfactory margin of uncertainty. This technique can be used to predict human fetal urinary flow rate with an expected accuracy of +/- 35%.

Ultrasonographic evaluation of human fetal urinary flow rate: accuracy limits of bladder volume estimations

OBJECTIVES

This study was conducted to examine the reliability of fetal bladder volume predictions on the commonly used ovoid volume formula and to develop a simpler but equally accurate method requiring fewer measurements.

STUDY DESIGN

Nine hundred twenty seven measurements were obtained from 11 dead fetuses in a water bath. Known incremental volumes of saline solution were infused and the largest linear bladder dimensions length, depth, and width, were measured ultrasonographically. Bladder volumes were calculated with the ovoid volume formula, 4/3.pi.(Length.Depth.Width)/8, and compared with true volumes. The areas of the ultrasonographic planes observed during the measurement process were calculated and plotted against the true volume for regression analysis. The sagittal and coronal areas were converted into volumes with the regression equations 0.46323 + 1.39394. Sagittal area and 1.20640 + 1.07603. Coronal area, respectively.

RESULTS

The fetal bladder volumes from the ovoid formula had an average error of 6.4 ml, with a 95% confidence interval of +/- 14.1 ml. The fetal bladder volumes derived from sagittal and coronal area formulas had mean absolute errors of approximately 0 ml, with 95% confidence intervals of +/- 4.0 ml and +/- 4.4 ml, respectively. The best predictions were obtained with the sagittal area measurements.

CONCLUSIONS

The ovoid volume formula overpredicts fetal bladder volume and has a wide 95% confidence interval. This inaccuracy probably affects measurements of fetal urinary flow rates. Use of the sagittal or coronal area affords improved accuracy and is easier and more convenient.

Longitudinal assessment of amniotic fluid index

OBJECTIVE

To derive a longitudinal gestational reference range for amniotic fluid index and to compare it with the established cross-sectional reference range.

DESIGN

Longitudinal prospective study.

SETTING

Liverpool Maternity Hospital and Mill Road Maternity Hospital, both teaching hospitals in central Liverpool.

SUBJECTS

One hundred and fifteen pregnant women, in whom the expected date by the last menstrual period and ultrasound scan at 18 to 19 weeks were in agreement by seven days, were recruited. They were divided into two groups and scanned at four weekly intervals as follows: Group A: scanned at 20, 24, 28, 32, 36, 40; and Group B: scanned at 22, 26, 30, 34, 38, 42.

RESULTS

Amniotic fluid index varies with gestation, rising from early gestation to peak at 30 weeks and then falling from 36 to 42 weeks. Comparison of our reference range with that of Moore and Cayle (1990) shows obvious differences at the lower limit.

CONCLUSION

We have established a normal longitudinal reference range for the amniotic fluid index. Our ranges, derived from longitudinal data, would seem a more appropriate reference than the established reference ranges derived from cross-sectional data. In particular, the differences at the lower limits may have considerable clinical implication in the use of amniotic fluid index in the prediction of fetal compromise.

Amniotic fluid volume: fluid dynamics and measurement technique

Evaluation of amniotic fluid volume is an important aspect of obstetrical ultrasound. Several methods are currently used to describe amniotic fluid volumes. The most common are the subjective assessment of fluid and the semiquantitative methods. The reproducibility of these methods is excellent in experienced hands. Because of the multiple methods used to assess fluid, both oligohydramnios and polyhydramnios have numerous definitions. Regardless of which definition is used, it is clear that both of these entities are associated with a variety of fetal and maternal conditions. Abnormal amniotic fluid volume may be the only or earliest sonographic sign of an obstetrical problem. Therefore, it is important that sonologists are familiar with amniotic fluid volume assessment. Although subjective and semiquantitative techniques may produce similar results, a numerical scale is no substitute for experience and training. One should be able to recognize lesser degrees of fluid abnormality and be able to assess the trend of amniotic fluid volume in serial examinations.

Sonographic imaging of the bovine fetus

Transrectal sonography documenting the anatomical features of 71 bovine fetuses was performed between Day 30 and 10 mo of gestation. Sector scanners, which have a wider field of view into the depth of the uterus, were used, and it was found that most macroscopic organs were visible with B-scan ultrasound. The first organ detected around the end of the first month of pregnancy was the heart. The orbit, the stomach and the braincase were identified at Day 40. Most bones of the skeleton and the scrotum appeared around Month 3. Characteristic sonographic images of the head, neck, vertebral column, thorax, stomach, liver, kidneys, urinary bladder, limbs, scrotum-respectively teats, as well as the umbilical cord, amnion and allantois are described in this study.

Relation of rate of urine production to oxygen tension in small-for-gestational-age fetuses

Hourly fetal urine production rate was determined by real-time ultrasonography immediately before cordocentesis for blood gas analysis in 27 small-for-gestational-age fetuses at 20 to 37 weeks' gestation; in 14 cases there was associated oligohydramnios. The values were compared with those of 101 appropriate-for-gestational-age fetuses. The hourly fetal urine production rate was significantly lower in the small-for-gestational-age fetuses than in the appropriate-for-gestational-age fetuses. Furthermore, there was a significant correlation between the degree of decrease in urine production and both the degree of fetal hypoxemia and the degree of fetal smallness. There was no significant difference between the oligohydramnios and nonoligohydramnios groups in either the degree of decrease in urine production or the degree of fetal hypoxemia.

Measurement of fetal urine production in normal pregnancy by real-time ultrasonography

Serial measurements of fetal bladder volume were obtained by real-time ultrasonography at 2- to 5-minute intervals, and the hourly fetal urine production rate was calculated. The mean hourly fetal urine production rate increased from 5 ml/hr at 20 weeks' gestation to 51 ml/hr at 40 weeks. These values are double those reported in previous studies that measured fetal bladder volumes at 15- to 30-minute intervals because the cycle length is shorter than previously thought.

Fetal renal failure associated with intrauterine growth retardation

Four preterm infants with severe intrauterine growth retardation had renal failure from birth. The amount of asphyxia associated with the birth process did not fully explain the renal failure. Before delivery all for fetuses had severe oligohydramnios and an empty urinary bladder. These observations strengthen the view that severe intrauterine growth retardation may be accompanied by oligohydramnios caused by fetal renal failure.

Fetal kidney volume and urine production in cases of fetal growth retardation

The amount of amniotic fluid has a close correlation to the function of the fetal renal system. In many cases of fetal growth retardation oligohydramnios is obvious. The aim of this study is the investigation of the hourly fetal urine production rate (HFUPR) and the growth of fetal kidneys during pregnancy in cases of fetal growth retardation and to evaluate the renal participation in the origin of oligohydramnios in cases of growth retardation. In 52 healthy pregnancies and 27 cases with known fetal growth retardation, the volume of the fetal kidneys was measured sonographically and the hourly rate of fetal urine production was determined. Two third of the patients with fetal growth retardation had obvious oligohydramnios. In cases of fetal growth retardation the volume of the fetal kidneys was significantly smaller when compared to the control group, and the volume of fetal urine production was significantly lower. The reduced perfusion of the fetal kidneys in those cases with fetal growth retardation may be the reason for the reduction of the HFUPR. Due to the fact that HFUPR is a dynamical parameter and in close relationship to the perfusion of the fetal kidneys, the identification and measurement of this parameter may help to detect subacute and imminent fetal distress in cases of sonographically proven fetal growth retardation.

Evaluation of renal function and acute renal failure in the neonate

The diagnosis of renal dysfunction in the neonate can be a challenging problem for the practicing pediatrician. Although there are real differences in renal function between term and preterm infants, overall function is quite adequate in both groups when fluid intake and environmental conditions are carefully controlled. When confronted with an infant with a pathologic decrease in urine output, the clinician must provide adequate fluid resuscitation for the infant with prerenal oliguria without inducing fluid overload in the infant with established, intrinsic renal failure. In addition, the infant with obstruction to urine flow must be distinguished. This requires careful assessment of physical findings and a few key laboratory determinations. Once the diagnosis of renal failure is made, frequent clinical monitoring with anticipation of potential complications is critical. Long-term management of renal failure in infancy and intervention for suspected urinary tract malformation in the fetus have emerged as difficult medical and ethical problems as our technology has advanced.

Amniotic fluid ionic concentration in response to chronic fetal vasopressin infusion

Chronically prepared, third trimester fetal lambs were administered 72-h intravenous infusions of arginine vasopressin (AVP) (65 or 130 mU/kg h) or 0.9% saline. Saline infusion preceding the AVP infusion did not change amniotic fluid (AF) composition. During the AVP infusion, there were significant increases in amniotic fluid osmolality (278.8 +/- 4.9 to 302.1 +/- 4.5 mosm) and in sodium (122.7 +/- 3.3 to 135.3 +/- 3.6 meq/l) and potassium (9.7 +/- 2.6 to 13.8 +/- 1.3 meq/l) concentrations. Saline infusion after the AVP infusion resulted in return of AF osmolality, sodium, and potassium toward normal levels. Fetal plasma and amniotic fluid AVP levels measured by radioimmunoassay significantly increased during AVP infusion and decreased during the subsequent saline infusion. There were no changes in maternal or fetal plasma osmolality in response to AVP. These results suggest that fetal AVP released in response to intrauterine stress may alter the composition and osmolality of amniotic fluid in a reversible manner.

Ultrasonographic anatomy and physiology of the fetal kidney

The aim of this work was to demonstrate the impact of ultrasonography in utero to gain a better understanding of the anatomy, growth, anatomical variations and function of the fetal kidney and urinary tract. Three main topics are discussed in this paper based on the authors' personal experience and data from the literature: 1) the technique of ultrasonography in utero, including the main difficulties encountered and limitations of this technique; 2) ultrasonographic study of the morphology, growth and anatomical variations of the fetal kidney. The length of the fetal kidney was found to be the most significant parameter for assessment of its growth. At term, the kidney measures slightly more than 4 cm in length, while the renal pelvis is usually no more than 10 mm thick; 3) current knowledge of the physiology of the fetal urinary apparatus especially the kidney. Excretory function of the kidney begins in the third month of gestation and its main role involves the regulation of the amniotic fluid.

Ovine fetal urine production following maternal intravenous furosemide administration

The response of the ovine fetus to maternal furosemide administration was studied in six chronically catheterized fetal lamb preparations. These studies indicate that in the chronic sheep model maternally administered diuretics do not augment fetal urine production. Additionally, passage of the drug from the maternal intravascular compartment to the fetal intravascular compartment could not be demonstrated. It is suggested that on the basis of these data, the results of the "Lasix challenge test" should be interpreted with caution when they are used to evaluate human fetal renal function.

Ultrasound diagnosis and perinatal management of surgically correctable fetal malformations

Among 276 fetal malformations detected during the nine year period there were 97 potentially correctable anomalies which are described in detail as are the antenatal and postnatal corrective procedures undertaken. On 35 hydrocephalic fetuses 9 were operated upon postnatally in the last 2 yr. Three months after the operation four of the babies were found to be developing normally, three moderately well while two were severely retarded. Two out six babies with cystic hygroma were successfully operated after birth and their development is now normal. Of 23 malformations of the gastro-intestinal tract (two diaphragmatic hernias, three esophageal, four duodenal and four jejunal atresias, seven omphalocele, three gastroschisis) 13 babies were successfully operated and are developing normally. In 8 out of 10 antenatally detected cases of obstructive uropathy antenatal intervention was undertaken. In one case a shunt catheter was inserted for the last three weeks before delivery. Puncture and urine evacuation was performed in seven of the babies. Five were live born and surgical correction was successfully undertaken after birth, while two died (one multiple malformations and the other respiratory distress syndrome). After excluding multiple and chromosomal anomalies the best results are obtained in the correction of gastro-intestinal tract atresia (9 of 11) and obstructive uropathy (5 of 7), where once a passage has been established the baby develops normally. Interventions such as shunts in hydrocephalic babies are always a matter for discussion in relation to the final outcome, but when there is no other choice, this too is a way of endeavouring to help such a baby. Early antenatal diagnosis is therefore extremely important when interruption of pregnancy is still feasible. In cases of malformations detected at a later gestational age early diagnosis facilitates the assessment of the development of the affected organ, possible timely antenatal correction, team consultation regarding the time and mode of delivery and preparations for postnatal correction. Such an antenatal approach makes it possible to significantly influence the perinatal outcome.