Background
Ultrasonography is a non-invasive and accurate diagnostic method to evaluate urinary system and its anomalies in the neonates. Kidney sonographic measurement can be used as an alternative method to estimate gestational age. The aim of this study was to measure kidney size in preterm neonates and to provide a guide reference for gestational age.
Materials and Methods: Four hundred kidneys (in both sides) of 200 preterm neonates born with gestational age less than 37 weeks were evaluated in the present cross sectional study. Newborns with intrauterine growth retardation (IUGR), asphyxia, high grade hydronephrosis, single kidney, polycystic kidney, duplex kidney, dysplastic kidney and hydroureteronephrosis were excluded. Ultrasound investigations were performed in supine and lateral decubitus positions. Birth weight, gestational age, height and sex were recorded. Data were analyzed using SPSS software version 16.0. 
Results: The mean gestational age of patients was 33.8±2.2 weeks. Mean kidney length, width, and thickness were 38.8±3.8 mm, 18.9±2.6 mm, and 21.3±2.6 mm, respectively. In addition, the kidney volume was 84037±2533.4 mm3. Mean diameter of the kidney and its volume were significantly higher in male neonates (p <0.05). Kidneys length and volume had a strong correlation with neonatal birth weight (r =0.608, p <0.001, r =0.663, p <0.001, respectively).
Conclusion
A significant positive correlation was observed between renal dimensions and birth weight, gestational age, and height of patients. The results of this study showed that the trend of kidney growth can be used as a reference guide for gestational age in premature neonates.