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Table of Contents
Year : 2018  |  Volume : 1  |  Issue : 1  |  Page : 8-11

Kidney length in healthy term neonates

1 Department of Pediatrics, Bharati Vidyapeeth University Medical College, Pune, Maharashtra, India
2 Department of Radiology, Bharati Vidyapeeth University Medical College, Pune, Maharashtra, India

Date of Web Publication28-Jun-2018

Correspondence Address:
Jyoti Sharma
A7, 702, Ganga Satellite, Wanowrie, Pune - 411 040, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/AJPN.AJPN_10_18

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Introduction: There is a lack of data on kidney size in Indian neonates, their determinants, and how the sizes compare with neonatal kidney sizes reported elsewhere. Methods: This cross-sectional study of renal size on ultrasonography was conducted in 765 consecutive healthy term neonates over 1 year at a single center. Multivariable regression analysis was used to examine the relationship of kidney length and volume with neonatal anthropometric variables and maternal characteristics. Information on kidney size was compared with published reports. Results: The mean ± standard deviation for the length of the right and left kidney were 38.6 ± 2.2 mm and 38.9 ± 2.2 mm, respectively, while the estimated kidney volume of the right and left kidney was 7.7 ± 1.7 ml and 8.3 ± 1.9 ml, respectively. Birth weight and neonatal length were independent predictors of renal length. Kidney length and volume in the present study were significantly lower as compared to that reported in the studies from outside south Asia. Conclusions: Kidney length in Indian term neonates depends on neonatal weight and length and is smaller in comparison to neonates from outside south Asia.

Keywords: Kidney volume, newborn, ultrasound

How to cite this article:
Malshe N, Joshi P, Ranchhod LA, Tapryal N, Sharma J. Kidney length in healthy term neonates. Asian J Pediatr Nephrol 2018;1:8-11

How to cite this URL:
Malshe N, Joshi P, Ranchhod LA, Tapryal N, Sharma J. Kidney length in healthy term neonates. Asian J Pediatr Nephrol [serial online] 2018 [cited 2022 Jul 7];1:8-11. Available from: https://www.ajpn-online.org/text.asp?2018/1/1/8/235470

  Introduction Top

Studies in Caucasian children indicate that kidney dimensions (length, width, and volume) vary with body length, weight and gestational age, and form the basis of nomograms.[1] Due to their smaller size, Indian newborns are expected to have smaller kidneys compared to neonates from other regions; however, precise information on range of kidney sizes in healthy term Indian newborns is not available or is limited to small studies across childhood.[2],[3],[4],[5],[6],[7],[8],[9] This information is important as small renal size is linked to altered developmental programming with reduced nephron number and might be a surrogate for hypertension and kidney disease in adulthood.[1] The present cross-sectional study determined kidney size in healthy term neonates at a teaching hospital in India using ultrasonologically measured kidney length, known to be feasible, reproducible, and clinically useful.[10],[11]

  Methods Top


This cross-sectional observational study was conducted on consecutive term neonates delivered at a tertiary care hospital attached to a University Medical College over 1 year. Following ethical approval and informed parental consent, we included term (≥37 weeks of gestation) babies who did not require special care and were roomed in with mothers. Neonates with visible congenital anomalies and those with antenatal or postnatal ultrasound suggesting renal anomaly(ies) were excluded from the study. Baseline information included neonatal age (hr), gestation, length and weight (measured using infantometer and digital weighing scale, respectively), and body surface area (calculated using Mosteller formula). Significant maternal history included anemia, hypertension, diabetes or heart disease.


Ultrasonography was used to measure kidney size between 48 and 96 hr of life by a single radiologist using a real-time machine (either Siemens G60 or Philips IU22) with a linear transducer of 3–9 MHz frequency. Infants were examined after feeding to facilitate the evaluation. All measurements of renal size (length, width, and depth) were conducted in the prone position twice on each side, and an average of two values was recorded. Kidney volume, in ml, was calculated by the equation for a prolate ellipsoid as follows: length (mm) × thickness (mm) × width (mm) × 0.523.[12]


Kidney measurements are presented as mean ± standard deviation (SD). Correlations between measurements of the two sides and between parameters are reported using Pearson's r with 95% confidence intervals (CI). Multivariable regression analysis was used to assess the effect of neonatal and maternal characteristics on kidney measurements. Two-sample t-tests were used to compare kidney measurements between studies. All calculations were performed on NCSS statistical software (version 2009; Kaysville, Utah, USA; ncss.com/software/ncss) with P < 0.05 considered statistically significant.

  Results Top


Of 1846 newborns delivered over 1 year, we excluded 651 neonates admitted to the intensive care unit, including 26 with antenatally or postnatally detected anomalies and 404 born while the radiologist was unavailable. Of 765 healthy term neonates included at mean ± SD gestational age of 39.0 ± 1.3 weeks, 337 (44%) were female. The average birth weight and neonatal length were 2.8 ± 0.4 kg and 46.8 ± 2.0 cm, respectively. The average maternal age was 24.1 ± 3.8 years; 49 (6.3%) mothers had pregnancy-induced hypertension while 152 (19.8%) had anemia.


Mean kidney length was 38.6 ± 2.2 mm on the right and 38.9 ± 2.2 mm on the left, with a significant correlation between the two (r = 0.60; 95% CI 0.55, 0.64). Similar correlation was observed between the width of the right (20.8 ± 1.0 mm) and left (20.2 ± 1.0 mm) kidney (r = 0.48; 95% CI 0.42, 0.53) and the respective depths (21.3 ± 1.0 mm versus 20.3 ± 1.0 mm; r = 0.42; 95% CI 0.36, 0.48).

Determinants of kidney size

On multiple regression, renal length was determined independently by birth weight and neonatal length, with a stronger relationship with the former than latter [Table 1]. The only independent predictor of kidney volume was birth weight [Table 1]. Kidney size was not affected by gender, gestational age, maternal age, or presence of maternal anemia.
Table 1: Multiple regression analysis for kidney length and volume

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Comparison of kidney size across studies

Comparison of mean kidney length and volume in the present study with studies from the United States of America, England, Nigeria and Bangladesh shows that Indian newborns have smaller kidneys than those in neonates from outside south Asia [Table 2] and [Table 3];[12],[13],[14],[15] kidney length among Indian newborns was comparable to that reported from Bangladesh.[16] Neonatal weight, reported in two studies (3.3 ± 0.5 kg [14] and 3.0 ± 0.4 kg [16]), was significantly higher than recorded in the present study (both P < 0.001).
Table 2: Comparison of kidney length in the present study with published reports

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Table 3: Comparison of kidney volume in the present study with published reports

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  Discussion Top

We performed ultrasonographic measurements of kidney size in 765 healthy term neonates born at a single center in India, examined their relationship to neonatal and maternal characteristics, and compared these measurements with data from other regions. We chose kidney length for its ease of measurement, reported accuracy, and good correlation with renal volume;[17] it is also the most common measure of serial change in kidney size. Kidney volume, calculated from three different measurements of the kidney, is likely to be less accurate since errors in any of three measurements would affect this result. While we did not record socioeconomic status, the results are generalizable to the largely vegetarian population belonging to semi-urban lower and lower-middle income groups catered to by the hospital.

We found that neonatal kidney length was positively correlated with weight and length at birth; however, the strength of their association was modest. Kidney size was closely correlated with body size in studies on neonates from Pakistan, Nigeria and India, and in two Indian studies on older children.[5],[6],[9],[15],[18] In contrast, there was no obvious correlation with weight or length in studies on infants from Serbia and Turkey.[11],[19] On multiple regression, we demonstrated that the effect of birth weight and length on kidney length persisted despite adjustments for gender, gestational age and maternal age and anemia. In addition, birth weight was more strongly correlated with kidney length than was birth length, while kidney volume was affected by birth weight alone. Multivariable regression was performed in only two studies in the past. While Gupta et al. reported that renal length correlates with body surface area,[9] Mishra et al. found that neonatal length, gestational age and postnatal age are independent predictors of combined kidney volumes in small for gestational age and appropriate for age babies.[20] Goodyer et al. reported that maternal vitamin A status may impact neonatal kidney size and that kidney volume is inversely correlated with serum creatinine, suggesting that kidney volume reflects functional renal mass.[21] Low birth weight and small kidney sizes are also correlated with increased salt sensitivity, indicating a mechanism for hypertension.[22] A longitudinal study from South India found that both birth weight and gestational age influence kidney growth and function through infancy.[23]

On comparing kidney size reported in various studies, we found that the kidney length and volumes of Indian term neonates was significantly smaller than that reported from other geographic regions, and was comparable only to the report from Bangladesh.[12],[13],[14],[15],[16] These findings suggest that Asian neonates have smaller kidneys than their counterparts in Africa, Europe, and America. Information on birth weight, limited to two of these studies, suggests that our newborns are significantly smaller than those included in studies with larger kidney sizes.[14],[16] Since renal volume appears to be linked to body size, the differences in kidney volumes between our and other studies could be attributed to the difference in birth weight. However, a study comparing 0–18 years old children from Hong Kong with age-matched children from Australia failed to find significant differences in kidney length, except in the 8–12 months age group, despite differences in body sizes across all ages.[24] However, the findings are difficult to interpret because of lack of details of anthropometry and small numbers studied in various age groups.

The strengths of our study are the large number of neonates studied and a homogenous study population of term healthy newborns. Previous studies have enrolled both preterm and term neonates, children across ages or have small numbers. Findings of small kidney sizes in Indian newborns as compared to that reported for Caucasians populations, form basis for larger studies for indigenous nomograms, as Western nomograms may not be applicable to Indian children.

An important shortcoming of our study is that all measurements were performed by a single ultrasonologist. This limitation is somewhat overcome by the fact that the strong correlation between the two kidney measurements suggests a high degree of reproducibility. Second, we excluded almost a thousand neonates born during the period of conduct of the study, potentially introducing selection bias. As a single-center study, the results may not be generalizable to the entire Indian population. Further, we would have liked to compare kidney length normalized to birth length and birth weight of our subjects with similarly normalized measurements from other countries in order to understand whether the kidneys of our neonates were truly small or proportionate in length to the body measurements. However, this comparison was not feasible since we did not have access to raw data of the other authors. In addition, we could not develop nomograms for kidney size in relation to gestational age or body length due to small numbers of newborns in each age or length category. Finally, as this was a cross-sectional study, we did not examine the long-term risk of kidney disease related to small kidney size as that requires longitudinal follow-up.

  Conclusions Top

Indian neonates have smaller renal length and volume than the newborns outside south Asia. Birth weight has a larger effect on kidney length than does neonatal length.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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[PUBMED]  [Full text]  
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Vujic A, Kosutic J, Bogdanovic R, Prijic S, Milicic B, Igrutinovic Z, et al. Sonographic assessment of normal kidney dimensions in the first year of life – A study of 992 healthy infants. Pediatr Nephrol 2007;22:1143-50.  Back to cited text no. 19
Mishra K, Datta V, Arushi A, Narula MK, Iyer RS, Nangia S. The association between weight for gestational age and kidney volume: A study in newborns in India. Iran J Pediatr 2014;2:30-7.  Back to cited text no. 20
Goodyer P, Kurpad A, Rekha S, Muthayya S, Dwarkanath P, Iyengar A, et al. Effects of maternal Vitamin A status on kidney development: A pilot study. Pediatr Nephrol 2007;22:209-14.  Back to cited text no. 21
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  [Table 1], [Table 2], [Table 3]


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