THIEME

18 Original Article

Accuracy of the Fetal Kidney Length Measurement by Ultrasonography in the Determination of the Gestational Age in PregnancyElangovan Muthaian1 Karthick Selvaraj2

1Department of Anatomy, Dhanalakshmi Srinivasan Medical College and Hospital, Perambalur, Tamil Nadu, India

2Department of Anatomy, Melmaruvathur Adhiparasakthi Institute of Medical Sciences and Research, Melmaruvathur, Tamil Nadu, India

Address for correspondence S. Karthick, MD, Department of Anatomy, Melmaruvathur Adhiparasakthi Institute of Medical Sciences and Research, Melmaruvathur, Tamil Nadu, India (e-mail: drkarthick.anat@gmail.com).

Background Definitive calculation of gestational age (GA) forms the basis for rendering standard antenatal care. Depending on the period of pregnancy, various parameters are in use for GA calculation. But none of those fetal biometric indices were observed to be reliable with progression of pregnancy beyond second trimester. Various studies claiming fetal kidney length (FKL) as a reliable index to calculate GA in late trimester have prompted this study to validate and compare this claim with other indices among Indian women in late pregnancy.Materials and Methods This study was done on 100 singleton uncomplicated late pregnant women who knew their last menstrual period definitely. A blinded sonographic process was executed wherein one sonologist measured traditional biometric indices like biparietal diameter, head circumference, abdominal circumfe- rence, and femur length and calculated GA. While the other measured only FKL and calculated GA. The results were descriptively analyzed. The correlation of each of the index in accurately calculating GA was done by Pearson’s correlation test.Results FKL was 28.12 mm at 28 weeks and it progressively increased along with GA and it was 40.10 mm at 40 weeks’ gestation. The Pearson’s correlation coefficient of r = 0.926 was observed to be significant compared with other fetal biometric indices measured.Conclusion FKL could be used as a single index to calculate GA in third trimester. Combined with other sonographic fetal indices FKL might increase the accuracy of GA calculation in late pregnancy.

Abstract

Keywords ► fetal kidney length ► gestational age ► ultrasound

Natl J Clin Anat 2019;8:18–21

DOI https://doi.org/ 10.1055/s-0039-1688532 ISSN 2277-4025.eISSN 2321-2780.

©2019 Society of Clinical Anatomists

IntroductionAccurate knowledge of gestational age (GA) is key for better antenatal care, planning, and successful management of all pregnancies. In high-risk pregnancies like preeclampsia, intrauterine growth retardation, gestational diabetes mellitus, and termination of pregnancy is planned considering the GA. Failure in accurate estimation of GA can result in iatrogenic prematurity or postmaturity, both of which are associated with increased perinatal mortality and morbidity.

Number of parameters have been in use to calculate GA. Depending on the trimester of pregnancy, first date of

last menstrual period (LMP), gestational sac diameter and volume, crown–rump length (CRL) measurements, biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL) are the traditional indices measured by ultrasonography to calculate GA.1–9 But there exist limited value for first trimester parameters like LMP and CRL. And also there happens increasing unreliability in using the other second trimester fetal biometric indices like BPD, HC, AC, and FL in GA estimation.10–13

The quest of finding an accurate sonographic predictor of GA during late pregnancy beyond second trimester resulted

Published online: 2019-04-28

19Fetal Kidney Size in Gestation Muthaian, Selvaraj

National Journal of Clinical Anatomy Vol. 8 No. 1/2019

in many studies which found fetal kidney length (FKL) as a potential index.12,14–20

Rule of thumb states that “renal length in millimeter approximates fetal GA in weeks.” Studies have also noted a linear increase in FKL with increase in GA.21–31 The growth of fetal kidney was shown to be 1.07 to 1.1 mm by a couple of studies.32,33 The fetal kidneys were claimed to have a constant increase in length of 1.7 mm fortnightly.34 This constant growth pattern of fetal kidneys remains unaltered by fetal growth disorders and so this parameter stands as a more reliable index for calculating GA even for complicated pregnancy.11,17

Limited Indian studies validating FKL and GA prompted this study. This study also compared the accuracy of FKL with other second trimester indices which are being used traditionally for GA estimation in late pregnancy.

Materials and MethodsThe study was done prospectively in a convenient sample size of pregnant women who got registered to the antenatal clinical of a rural medical college hospital during November 2013 to March 2014. Only those pregnant women who knew their LMP with singleton fetus in their third trimester were enrolled in this study irrespective of their parity and maternal age. Women with doubtful LMP, having pregnancy associated with risk factors, anomalies, and who were in their first and second trimester were excluded even if they happened to be registered to antenatal care of the hospital.

All the enrolled women were subjected to blinded sonographic examination by two experienced sonologist using Mindray DC 70 expert ultrasound instrument with convex probe in a frequency of 3.5 to 5. Among them, one sonologist limited his examination to traditional biomet-ric indices measured for calculating GA like AC, HC, FL, and BPD. From the measured indices the GA was calculated using Hadlock’s formula,35 while the other sonologist was made to measure only the FKL as described by Bertagnoli et al.15

The measured indices were tabulated and descriptive statistics were applied. The correlation between GA and traditional indices and FKL was done by Pearson’s correlation method.

The study was done only after obtaining institutional ethi-cal clearance and informed consent from enrolled participants.

ResultsA total of 100 women with the age ranging from 21 to 36 years completed the study. Both right and left kidneys were measured and its average was used for computation of renal length which was found to be 28.12 and 40.1 mm in 28 and 40 weeks of gestation, respectively (►Table  1). It was observed that the renal length in millimeters at any given GA corresponds to the GA of the fetus. The mean FKL for third trimester was 34.1 mm.

A positive correlation was observed between all indices and GA. The correlation between GA and mean FKL was seen to be highly significant with Pearson’s correlation (p < 0.001) (►Table 2).

DiscussionProper antenatal care depends largely upon GA measure-ment. When women register late and in particular those who are uncertain of their LMP, it is often difficult to date pregnancies. Clinical dating methods like LMP and uterine size and sonographic indices like CRL, BPD, HC, FL, and AC had been shown to fail in accurate GA calculation beyond 28 weeks of gestation.1–13

FKL was reported to be a reliable index in late pregnancy GA estimation.12,14–20

The mean FKL measured in this study was observed to linearly increase with increasing GA (►Table 1). The mean FKL with GA was compared with previous studies. It was found to coincide with most studies except two studies which reported slightly higher values (►Table3). The higher values seen in those two studies could be due to ethnicity. The mean FKL for pregnancy beyond 28 weeks obtained from this study was found well within reported range of 33.8–to 39.5 mm.26,30

GA was correlated with different fetal biometric indices and the correlation coefficient compared with that of FKL correlation coefficient. In this study, correlation coefficient showed more accurate GA with FKL compared with other in late pregnancy. Similar findings were shown in literature reports.21–31

During the first 10 weeks of pregnancy, LMPs and sonographic indices were claimed to predict GA to within 4.7 days1,2 and between 12 and 24 weeks, to within 6 to 10 days.3–9 The unreliability of the fetal biometric indices like BPD, HC, AC, and FL in calculating GA in late pregnancy have left place for using FKL as a reliable index. In third trimester using traditional fetal biometric indices, studies have reported GA with error of 6 to 9.45 days.19,36,37 Meanwhile with FKL added as an additional index, it was shown to increase accuracy with standard error of 5.54 days only.36

Table 1 Changes in fetal kidney length with gestational age

Gestational age (wk)

No. of cases Mean kidney length (mm)

SD

28 8 28.12 0.08

29 4 29.00 0.54

30 2 30.17 0.00

31 7 31.22 0.10

32 8 32.00 0.00

33 7 32.64 0.00

34 12 34.22 0.33

35 16 35.15 0.58

36 14 36.56 0.14

37 14 37.14 0.00

38 4 37.86 0.26

39 2 39.15 0.02

40 2 40.10 0.02

Abbreviation: SD, standard deviation.

20 Fetal Kidney Size in Gestation Muthaian, Selvaraj

National Journal of Clinical Anatomy Vol. 8 No. 1/2019

Even though this study validated and showed linear increase of FKL with progression of gestation, limited sample size and convenient sampling technique used might prove to be a limiting factor.

ConclusionWith a constant increase, FKL has shown a strong correla-tion with GA in third trimester pregnancy. Even though it could be used as standalone index in calculating GA beyond 28 weeks, it might be of advantage if it was added to other sonographic fetal biometric indices to bring in more accuracy to GA calculation.

Conflict of InterestNone.

FundingNone.

References

1 Hellman LM, Kobayashi M, Fillisti L, Lavenhar M, Cromb E. Growth and development of the human fetus prior to the twentieth week of gestation. Am J Obstet Gynecol 1969;103(6):789–800

2 Robinson HP, Fleming JE. A critical evaluation of sonar “crown-rump length” measurements. Br J Obstet Gynaecol 1975;82(9):702–710

3 Campbell S. The prediction of fetal maturity by ultrasonic measurement of the biparietal diameter. J Obstet Gynaecol Br Commonw 1969;76(7):603–609

4 Hadlock FP, Deter RL, Harrist RB, Park SK. Fetal biparietal diameter: a critical re-evaluation of the relation to menstrual age by means of real-time ultrasound. J Ultrasound Med 1982;1(3):97–104

5 Hadlock FP, Deter RL, Harrist RB, Park SK. Fetal head circumference: relation to menstrual age. AJR Am J Roentgenol 1982;138(4):649–653

6 O’Brien GD, Queenan JT, Campbell S. Assessment of gestational age in the second trimester by real-time ultrasound measurement of the femur length. Am J Obstet Gynecol 1981;139(5):540–545

7 Hadlock FP, Deter RL, Harrist RB, Park SK. Fetal abdominal circumference as a predictor of menstrual age. AJR Am J Roentgenol 1982;139(2):367–370

8 Hadlock FP, Harrist RB, Deter RL, Park SK. Fetal femur length as a predictor of menstrual age: sonographically measured. AJR Am J Roentgenol 1982;138(5):875–878

9 Egley CC, Seeds JW, Cefalo RC. Femur length versus biparietal diameter for estimating gestational age in the third trimester. Am J Perinatol 1986;3(2):77–79

10 Benson CB, Doubilet PM. Sonographic prediction of gestational age: accuracy of second- and third-trimester fetal measurements. AJR Am J Roentgenol 1991;157(6):1275–1277

11 Konje JC, Bell SC, Morton JJ, de Chazal R, Taylor DJ. Human fetal kidney morphometry during gestation and the rela-tionship between weight, kidney morphometry and plasma active renin concentration at birth. Clin Sci (Lond) 1996;91(2):169–175

12 Butt K, Lim K; Diagnostic Imaging Committee. Determination of gestational age by ultrasound. J Obstet Gynaecol Can 2014;36(2):171–181

13 Garg A, Goyal N, Gorea RK, Pathak N, Mohan P. Normogram from fetal kidney length by ultrasonographically. J Punjab Acad Forensic Med Toxicol 2015;15:14–16

14 Gonzales J, Gonzales M, Mary JY. Size and weight study of human kidney growth velocity during the last three months of pregnancy. Eur Urol 1980;6(1):37–44

15 Bertagnoli L, Lalatta F, Gallicchio R, et al. Quantitative characterization of the growth of the fetal kidney. J Clin Ultrasound 1983;11(7):349–356

16 Cohen HL, Cooper J, Eisenberg P, et al. Normal length of fetal kidneys: sonographic study in 397 obstetric patients. AJR Am J Roentgenol 1991;157(3):545–548

Table 2 Correlation of gestational age with kidney length and other parameters

Variables Test statistics AC HC BPD FL Kidney length

Gestational age Pearson’s correlation 0.882a 0.902a 0.924a 0.950a 0.962a

Significance (two-tailed) < 0.05 < 0.05 < 0.05 < 0.05 < 0.05

No. of cases 100 100 100 100 100

Abbreviations: AC, abdominal circumference; BPD, biparietal diameter; FL, femur length; HC, head circumference.aCorrelation is significant at the 0.05 level (two-tailed).

Table 3 Comparison of mean FKL among different studies

Gestational age (wk)

Sagi et al23 Kansaria and Parulekar29

Cohen et al16 Bertagnoli et al15 Ahmadi et al32 Present study

28 27.8 26.9 34 27.2 32.27 28.12

30 30.5 29.0 38 28.8 35.23 30.17

32 33.3 30.8 41 30.4 37.41 32.00

34 36.0 32.5 42 34.0 39.70 34.22

36 38.2 34.2 42 34.0 40.81 36.56

38 40.3 36.2 44 36.0 42.45 37.86

Abbreviation: FKL, fetal kidney length.

21Fetal Kidney Size in Gestation Muthaian, Selvaraj

National Journal of Clinical Anatomy Vol. 8 No. 1/2019

17 Konje JC, Okaro CI, Bell SC, de Chazal R, Taylor DJ. A cross-sectional study of changes in fetal renal size with gestation in appropriate- and small-for-gestational-age fetuses. Ultrasound Obstet Gynecol 1997;10(1):22–26

18 Gloor JM, Breckle RJ, Gehrking WC, et al. Fetal renal growth evaluated by prenatal ultrasound examination. Mayo Clin Proc 1997;72(2):124–129

19 Konje JC, Abrams KR, Bell SC, Taylor DJ. Determination of gestational age after the 24th week of gestation from fetal kidney length measurements. Ultrasound Obstet Gynecol 2002;19(6):592–597

20 Yusuf N, Moslem FN, Haque JA, et al. Fetal kidney length: can be a new parameter for determination of GA in 3rd trimester. TAJ 2007;20(2):147–150

21 Lawson T, Filey W, Berland L, Clark K. Ultrasonic evaluation of lens kidneys. Radiology 1981;138:153–156

22 Jeanty P, Dramaix-Wilmet M, Elkhazen N, Hubinont C, van Regemorter N. Measurements of fetal kidney growth on ultrasound. Radiology 1982;144(1):159–162

23 Sagi J, Vagman I, David MP, et al. Fetal kidney size related to gestational age. Gynecol Obstet Invest 1987;23(1):1–4

24 Sampaio FJ, Mandarim-de-Lacerda CA, Prates JC. Allometric study of renal growth in human fetuses. Surg Radiol Anat 1989;11(1):29–31

25 Scott JE, Wright B, Wilson G, Pearson IA, Matthews JN, Rose PG. Measuring the fetal kidney with ultrasonography. Br J Urol 1995;76(6):769–774

26 Ansari SM, Saha M, Paul AK, Mia SR, Sohel A, Karim R. Ultrasonographic study of 793 foetuses: measurement of normal foetal kidney lengths in Bangladesh. Australas Radiol 1997;41(1):3–5

27 Fong KW, Ryan G. Fetal urogenital tract. In: Rumack CM, Wilson SR, Charboneau JW, eds. Diagnostic Ultrasound. 2nd ed. Vol. 2. New York: Mosby Year Book Inc.; 1998:1093–10121

28 Chitty LS, Altman DG. Charts of fetal size: kidney and renal pelvis measurements. Prenat Diagn 2003;23(11):891–897

29 Kansaria JJ, Parulekar SV. Nomogram for foetal kidney length. Bombay Hosp J 2009;51(2);155-162

30 Nirmala Shivalingaiah Sowmya K, Ananya R, Kanmani TR, Marimuthu P. Fetal kidney length as a parameter for determi-nation of gestational age in pregnancy. Int J Reprod Contracept Obstet Gynecol 2014;3(2):424–427

31 Edevbie JP, Akhigbe AO. Ultrasound measurement of fetal kidney length in normal pregnancy and correlation with gestational age. Niger J Clin Pract 2018;21(8):960–966

32 Ahmadi F, Taqi Dizaj AV, Akhbari F, Hohreh Irani S, Holamreza Khalili G. Fetal kidney measurement in 26–39 weeks gestation in normal fetuses of Iranian pregnant women. J Pregnancy Child Health 2015;2:139

33 Filly PA, Feldstein VA. Ultrasound evaluation of normal fetal anatomy. In: Callen PW, ed. Ultrasonography in Obstetrics and Gynecology. 5th ed. Philadelphia: Saunders; 2007:342–343

34 Witzani L, Brugger PC, Hörmann M, Kasprian G, Csapone-Balassy C, Prayer D. Normal renal development investigated with fetal MRI. Eur J Radiol 2006;57(2):294–302

35 Hadlock FP, Harrist RB, Hohler CW. Determination of fetal age. In: Athey PA, Hadlock FP, eds. Ultrasound in Obstetrics and Gynaecology. 2nd ed. New Delhi: B.I. Churchill Livingstone Pvt. Ltd.; 1985:22–37

36 Gupta DP. Gupta HP, Zaidi Z, Saxena DK, Gupta RP. Accuracy in estimation of gestational age in third trimester by fetal kidney length in Indian women. Ind J Clin Practice 2013;24(5):459–463

37 Peter M, Nayak AK, Giri PP, Jain MK. Fetal kidney length as a parameter for determination of gestational age from 20th week to term in healthy women with uncomplicated pregnancy. Int J Res Med Sci 2017;5:1869–1873