ORIGINAL ARTICLE
ASSESSMENT OF GESTATIONAL AGE BY ULTRASONIC MEASUREMENT OF
FETAL KIDNEY LENGTH
S. Sathiya1, R. Sailatha2, K. Vijayalakshmi3, Vasantha N. Subbiah4, A.M.Famida5, S. Renuka6,
M.Sharadha7
HOWTOCITETHISARTICLE:
S. Sathiya, R. Sailatha, K. Vijayalakshmi, Vasantha N. Subbiah, A. M. Famida, S. Renuka, M. Sharadha.
“Assessment of Gestational Age by Ultrasonic Measurement of Fetal Kidney Length” .Journal of Evolution of
Medical and Dental Sciences 2014; Vol.3, Issue 01, January 06; Page: 230-234.
ABSTRACT: Ultrasound is a non-invasive, safe and useful diagnostic method used by most
Obstetricians to take certain important decisions in Obstetrics. Ultrasound is shown to be free from
risk to the mother and her unborn fetus as well. A prospective study was done in 139 pregnant
women after 28 weeks of pregnancy with known and unknown dates, whose gestational age were
confirmed by early scan. The aim of this study was to see if there lays a correlation between the fetal
kidney length and gestational age in III trimester. The kidney length showed a linear correlation as
gestational age progressed. Age, parity, sex of the infant, side of the kidney showed no significant
bearing in the assessment of renal length and its correlation to GA. The result obtained confirmed
that in addition to the other USG biometric values commonly and most extensively used (BPD, HC,
AC, FL), fetal kidney length can also be used as an important parameter for the confirmation of GA in
III trimester.
KEYWORDS: Pregnancy, Ultrasound, Fetal Kidney Length, Gestational Age.
INTRODUCTION: An accurate establishment of expected date of delivery is fundamental in the
management of Obstetrics. Proper assignment of expected date of delivery is necessary to obtain
and appropriately interpret laboratory tests, to plan and execute the rapeutic maneuvers and to
determine optional management of certain high risk pregnancies like IUGR, patients with diabetes,
severe pre-eclampsia, eclampsia and sensitized Rh–vemother etc.
The patient’s Last Menstrual Period(LMP) is considered adequate for the purpose of establishing
Estimated Delivery Date(EDD),only if her previous periods were at regular intervals and if patient
did not use OCP’s 3 months prior her last period. Next is positive urine pregnancy test (4–
5postmenstrual) for establishing EDD. Average duration of pregnancy is 266 days from conception
and 280 days from LMP in a woman with 28 days cycle. The major problem in this method is that the
ovulation time may vary in every cycle and in every individual. About20-30% of pregnant women
who are sure of their LMP date have a significant difference between their menstrualage and
ultrasonographic dating. Andersonetal1 demonstrated in a cohort study that only 71% were sure of
their LMP. The clinical measurement of uterine size or estimation of Gestational Age (GA)isnot100%
reliable due to many variables like Maternal Obesity, Position of Uterus, Amount of Amniotic Fluid,
Multiple Gestation, Observer Experience, Fetal growth disorders and Anomalous baby. Presently it
appears that the most effective way to date pregnancy is the use of USG. Even in a patient with
reliable clinical criteria one should have are altimeul trasound for confirmation. Several sonographic
derived parameters can be used to datepregnancy1,2.
I Trimester: Gestational Sac,Yolk Sac, Embryo, Cardiac Activity
II Trimesteronwards:BPD,AC,HC,FL
Journal of Evolution of Medical and Dental Sciences/Volume 3/Issue 01/ January 06, 2014
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ORIGINAL ARTICLE
Other USG parameters like Kidney length, Footlength, Length of Humerus,
ClavicleLength,Ventricular Size, Biocular distance can be used to assess the GA3,4.
The impact of USG on the practice of Obstetrics has been profound without biological
hazards. A part from iatrogenic prematurity, objective knowledge of the data is essential in the
managemen t of all pregnancies in particular with regard to the method of MTP, management of high
risk pregnancies, planned induction of labor or elective C-section.
The main aim of this study was to measure the fetal kidney length in patients with known
and unknown dates in II trimester, making it an important/vital parameter in determining the
gestational age and to determine the correlation between renal length and other parameters like
biparietal diameter, head circumference, abdominal circumference and femur length in assessing the
gestationalage.
MATERIALS AND METHODS: A prospective study was conducted in the department of Obstetrics &
Gynaecology, CHRI during the period May 2013 – November 2013. A total number of 150 patients
aged between 18 – 35 years attending the outpatient department for antenatal checkup were
studied after 28 weeks of pregnancy whose GA were confirmed by early USG (<12 weeks). Patients
with singleton pregnancy with known or unknown dates of LMP were included in the study. Patients
with known diabetes or hypertension, oligohydramnios, polyhydramnios, IUGR, multiple pregnancy,
chronic renal disease, severe anemia, gross maternal obesity and suspected fetal anomalies were
excluded from the study.
A thorough history collected from each patient. Clinical assessment of GA was done by
palpating the fundal height. Routine USG scanning was done with linear array real time ultrasound
machine equipped with 3.5MHz transducer and an initial survey, measurements needed for fetal
biometry (BPD, FL, HC & AC) was taken. The length of the fetal kidney both right and left was
measured and the mean value taken. Each patient was subjected to serial ultrasound and fetal
biometry and fetal kidney length taken every 2 weeks once from 28 weeks to 40 weeks of gestation.
The fetal kidney length was measured as described by Konje JC5,6. All the measurements were
performed during fetal apnea. For the kidney length measurements, the fetus was scanned in the
transverse plane until the kidneys were visualized just below the stomach. The probe was then
rotated through 90 to outline the longitudinal axis of the kidneys. The right and left kidneys were
measured twice and the mean of the measurements of the two kidneys was taken. Care was taken to
exclude the adrenal glands in the measurements.
Linear mixed regression models were used to examine the evidence of a linear relationship
between estimated gestational age and the various anthropometric measurements.
RESULTS AND ANALYSIS: Out of 150 antenatal women only 139 patients delivered in this hospital,
hence only 139 patients were included in this study. The results were analyzed with respect to the
age of the patient, parity, side of the fetal kidney measured, sex of the baby and birth weight.
Patient’sAge(years)
<19
20-29
30-34
>35
8
107
18
6
Table 1: Age of the patients in the study group
Journal of Evolution of Medical and Dental Sciences/Volume 3/Issue 01/ January 06, 2014
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ORIGINAL ARTICLE
Fig. 1: Parity of the patients
Fig. 3: Birth weight of the newborns
Fig. 2: Sex of the newborn
Fig. 4: GA during which the
study group delivered
DISCUSSION: Knowledge of GA is important to the obstetrician as it can affect the clinical
management in a number of important ways. Up to 40% of mothers who claim to know their
obstetric dates with certainty, there is in fact an error of more than 2 weeks when GA is calculated
with USG. A discrepancy of 2 weeks can be critical for the survival of an infant who has to be
delivered early because of some antenatal complication.
Standard measurements for renal circumference, volume, width, thickness and length have
been reported to increase throughout gestation. Renal length and anteroposterior diameter
represent the technically easiest measurement of renal size to obtain. A good rule of thumb is that
menstrual age in weeks approximates the normal fetal kidney length in millimeters or twice the AP
diameter in millimeters.
This study is compared with various other studies mostly done in countries like USA, UK,
Cuba, and Germany. There are only a few Indian studies in regard to the relation between gestational
age and renal length. So, this study was also done to find whether there exists any difference in
different ethnic groups.
This study was compared with Gonzales et al 7 and Grannum P et al8 and the results were
same showing that the kidney length increases as the gestational age progresses.
This Study was not able to show whether it can be used as predictor of IUGR.
Journal of Evolution of Medical and Dental Sciences/Volume 3/Issue 01/ January 06, 2014
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ORIGINAL ARTICLE
Unlike Hunter et al study9 this study showed no significant difference between right and left
kidney length and kidney length in male and female neonates were more or less the same.
This study analyzed the renal length and gestational age. A growth centile chart was
constructed and was compared with the table given by AJ of Radiology, 1991 and
CohenHLCooperT10. These measurements coincide with 95% confidence limit.
GestationalAge(Week RenalLength(m
RenalLengthinthisstudy(m 95%ConfidenceLim
s)
m)
m)
it
28
34
34
26-42
29
36
37
23-48
30
38
38
29-46
31
37
35
28–46
32
41
35
31-51
33
40
35
33-47
34
42
37
33-50
35
42
38
32-52
36
42
37
33-50
37
42
39
33-51
38
44
41
32-56
39
42
39
35-48
40
43
40
32-53
Table 2: Mean Renal Length - Various Gestational Ages as given by COHEN HL COOPER T
Finally to prove that this study is a well correlated study Pearsons correlation coefficient
formula was applied and using a statistical package a computer analyses was done with X as GA in
weeks and Y as renal length. According to this the correlation coefficient for 139 cases was sought. It
is 0.847 and has significant correlation. So it is found that determination of renal length and thereby
calculating GA is accurate and has got higher percentage of technical success than other parameters.
CONCLUSION: This study shows that age, parity, sex of the infant, side of the kidney shows no
significant bearing in the assessment of renal length and its correlation to GA. Several reports
concerning renal size in the live fetus have appeared in the last decade.
But few have had sufficient data to permit centile charts to be derived, although there are
numerous such charts available for other fetometric parameters. The present study has shown that
there is significant correlation between the renal length and GA particularly in III trimester. Still
more studies are required to determine the accuracy of correlation between renal length and other
parameters like BPD, AC, FL, and GA of the fetus to prevent preterm induction thereby reducing
perinatal mortality and morbidity.
REFERENCES:
1. Andersen HF. Johnson TRB. Flora JD.et al. GA assessment. Prediction from combined clinical
observations. Am J Obstet Gynecol 1981;140:770-74.
2. Drumm JE. The prediction of delivery date by ultrasonic measurement of fetal crown-rump
length. Br J Obstet Gynaecol 1977; 84: 1–5.
Journal of Evolution of Medical and Dental Sciences/Volume 3/Issue 01/ January 06, 2014
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ORIGINAL ARTICLE
3. Hadlock FP, Harrist RB, Shah YP, King DE, Park SK, Sharma RS.Estimating fetal age using
multiple parameters: a prospective evaluation in a racially mixed population. Am J Obstet
Gynecol 1987;156: 955–7.
4. Hadlock FP, Kent WR,LoydJR, Harrist RB, Deter RL. An evaluation of two methods for
measuring fetal head and body circumferences. JUltrasoundMed1982;1:359–60.
5. Konje JC, Bell SC, Morton JJ, de Chazal R, Taylor DJ. Human fetal kidney morphometry during
gestation and the relationship between weight,kidney morphometry and plasma active rennin
concentration as birth. Clin Sci 1996; 91: 169–75.
6. 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 Jul;10(1):22-6.
7. Gonzales J.Gonzales M.Mary JY. Size and weight study of human kidney growth velocity during
last three months of pregnancy. Ear Urol 1980:6:37-44.
8. Grannum P, Bracken M, Silverman R, Hobbins JC. Assessment of fetal kidney size in normal
gestation by comparison of ratio of kidney circumference to abdominal circumference. Am J
Obstet Gynecol 1980, 136: 249-254.
9. Scott JES, Hunter EW, Lee REJ, Matthews JNS. Ultrasound measurement of renal size in
newborn infants. Arch Dis Child 1990; 65: 361-364.
10. Cohen HL, Cooper J, Einsenberg P, Mandel FS, Gross BR,Goldman MA, Barxel E, Rawlinson KF.
Normal length of fetal kidneys: Sonographic study of 397 obstetric patients. AJR Am J
Roentgenol 1991; 157: 545–48.
AUTHORS:
1. S. Sathiya
2. R. Sailatha
3. K. Vijayalakshmi
4. Vasantha N. Subbiah
5. A.M. Famida
6. S. Renuka
7. M. Sharadha
PARTICULARS OF CONTRIBUTORS:
1. Assistant Professor, Department of Obstetrics
and Gynaecology, Chettinad Hospital and
Research Institute.
2. Assistant Professor, Department of Obstetrics
and Gynaecology, Chettinad Hospital and
Research Institute.
3. Associate Professor, Department of Obstetrics
and Gynaecology, Chettinad Hospital and
Research Institute.
4. Professor, Department of Obstetrics and
Gynaecology, Chettinad Hospital and Research
Institute.
5.
6.
7.
Professor, Department of Obstetrics and
Gynaecology, Chettinad Hospital and
Research Institute.
Assistant
Professor,
Department
of
Obstetrics and Gynaecology, Chettinad
Hospital and Research Institute.
Assistant
Professor,
Department
of
Obstetrics and Gynaecology, Chettinad
Hospital and Research Institute.
NAME ADDRESS EMAIL ID OF THE
CORRESPONDING AUTHOR:
Dr. Sathiya.,
No. 31/14, Srishty Apartments,
Vinayagampet Street, Saidapet,
Chennai – 600015.
Email- s.sathiya.dr@gmail.com
Date of Submission: 18/12/2013.
Date of Peer Review: 19/12/2013.
Date of Acceptance: 24/12/2013.
Date of Publishing: 06/01/2014
Journal of Evolution of Medical and Dental Sciences/Volume 3/Issue 01/ January 06, 2014
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