47Summary Introduction. Neonatal anthropometric measurements, including body weight, length, head circumference and abdominal circumference are routine procedures in obstetric and neonatal departments. Standard values for neonatal population are established for body weight, length, head and thoracic circumference, however there are no reference values for neonatal abdominal circumference, futhermore, this measurement currently is not a routine procedure in every obstetric and neonatal unit. In order to evaluate the increase of abdominal circumference in newborns with a disease of organs of abdominal cavity including necrotizing enterocolitis (NEC), the abdominal girth of newborns soon after birth without pathology in the abdominal cavity should be ascertained. Thereby, the average value of the abdominal circumference of newborns in Latvia could be obtained. Aim of the Study. The aim of our study is to measure the abdominal circumference in premature and term-born neonates soon after birth and to define the correlation between abdominal circuit and birth weight. Materials and Methods. The measurement of waist girth was carried out in 460 neonates within 30 minutes after birth. Newborns were divided into 4 groups according to birth weight: extremely low birth weight (ELBW) -under 1000 g, very low birth weight (VLBW) -1001 g -1500 g, low birth weight (LBW) -1501 g -2500 g and term neonates with 2501 g -4590 g birth weight. The abdominal circumference was measured in 2 obstetric units in accordance with the previously established measurement methods.Results. There was no statistical difference between abdominal circumference in boys and girls in ELBW, VLBW and LBW groups (p>0.05). Mean abdominal circumference in ELBW group was 18,70 cm (SD=0,84) in boys and 18,67 cm (SD=1,40) in girls, VLBW group was 22,20 cm (SD=1,42) and 21,94 cm (SD=1,29) in boys and girls, respectively. Mean abdominal circumference in LBW group was 24.47 cm (SD=2.36) in boys, and 24.92 cm (SD=2.23) in girls. Independent Samples Test: Mean abdominal circumference was statistically different in boys and girls in 2500g -4590g birth weight group with median value 30.56 cm in boys, and 33.23 cm in girls (p<0,05). Mean value in girls was 3.33 cm higher than in boys. Dependent Variable linear regression: Specific formula for estimation of normal abdominal circumference was developed as a result of this study: y=0.0044x+16.38 (y -abdominal circumference, cm; x -body weight, grams; 0.0044 -regression coefficient; 16.38 -regression constant). Conclusions. The difference of mean abdominal circumference was not statistically significant in boys and girls in ELBW, VLBW and LBW groups, however, the difference was significant in the term-born neonates group. As a result of this study reference values and specific formula were established, which allows determination of normal abdominal circumference in neonates depending on birth weight.