Subjects
Thirteen caucasian pregnant women were enrolled for the study among the pregnant patients followed from January to December 2007 at the Author's Institution. Inclusion criteria were presence of IUGR and singleton pregnancy. Exclusion criteria were: gestational diabetes, smoking, alcohol abuse, drug addiction, abnormal fetal karyotype, fetal malformations and infections. Gestational age was calculated from the last menstrual period and confirmed by routine ultrasonography at 11-13 weeks of gestation [10].
IUGR was defined by the occurrence of a fetal abdominal circumference below the 10th centile of reference values for fetuses of similar ages and a decrease of more than 40 percentiles from the age specific size curve [11].The study was approved by the local Institutional Review Board. Informed consent was obtained from all pregnant women prior to the beginning of the study.
In utero ultrasound evaluation
A fetal ultrasound evaluation was performed within 4 hours before the delivery. A 5 MHz convex probe was used for all measurements (Voluson 730 Expert-GE Medical Systems). During the examination, routine ultrasonographic biometric parameters including head circumference, bi-parietal diameter, abdominal circumference and femur length were obtained together with a more complex evaluation of fetal fat mass. Ultrasound measurements of fat were obtained on cross-sectional images of the proximal arm and the abdomen as previously described by Bernstein and colleagues [12] and more recently by Galan and colleagues [8]. A longitudinal view of the long bone was obtained and used to identify the midpoint of the arm. The transducer was then rotated 90° to obtain the cross-sectional view of the mid-limb. Fat body mass area of the mid upper arm was measured by taking the total cross-sectional limb area and subtracting the central lean area consisting of muscle and bone on axial ultrasound images (Figure 1).
The fat mass of the abdomen was determined by measuring the thickness of the anterior abdominal subcutaneous tissue on the same axial image on which the abdominal circumference was obtained[13] and positioning the caliper on the proximal midaxillary line (Figure 2).
Subscapular fat thickness was evaluated longitudinally on the fetal trunk, visualizing the entire scapula, positioning the caliper between the skin surface and the subcutaneous tissue at the interface with the super- and infra-spinous muscles (Figure 3) [7].
Two measurements were made for each of these parameters and the mean value was used in the analysis. All the measurements were performed by the same trained operator. The intraobserver coefficient of variation for the abdominal proximal arm and subscapular subcutaneous thickness was 2.6%, 2%, 2.1%, respectively (unpublished observations).
Mothers' age, pre-pregnancy weight, height and BMI (kg/m2) and weight increase during pregnancy were collected as maternal variables. The placental weight was also recorded.
Neonatal anthropometric measurements
Anthropometric measurements (weight, length and head circumference) and subcutaneous skinfold thicknesses were assessed in all infants on the first day of life by the same trained operator. The investigator who performed the postnatal measurements was blinded to the antenatal results.
Body weight, length and head circumference were measured according to standard procedures [14]. Babies weight was measured on an electronic scale accurate to ±5 g (Seca scale, Intermed s.r.l. San Giuliano Milanese, Milano, Italy) and body length was measured to the nearest millimeter on a Harpenden neonatometer (Holtain Ltd, UK). Head circumference was measured to the nearest millimeter with non-stretch measuring tape.
Left skinfold thicknesses were measured using a commercial caliper (Harpenden Skinfold Caliper, Baty International, West Sussex, UK) at the following sites: biceps, triceps, subscapular and suprailiac. Skinfold thicknesses were assessed three times and the mean of three readings was taken.
The skinfolds were measured by elevating a fold of skin and subcutaneous tissue between the operator's thumb and index, from the underlying muscle tissue [15, 16]. The intra-observer repeatability was 0,20 mm. Triceps skinfolds were measured at the level of the mid-arm circumferences between the acromion and the olcranon processes. Biceps was measured at the same level but on the anterior arm's surface. Immediately below the lower angle of the scapula, subscapular skinfold was measured. Suprailiac skinfold was measured immediately above the iliac crest, 1 cm towards the medial line. In order to account for the fluctuation in total body water that occurs during the early days of life, dynamic skinfold thickness was obtained by reading each skinfold thickeness after a 60 second pressure [17]. All measurements were to the nearest mm.
Statistical analysis
Descriptive data are expressed as mean (SD) or number of observations (percentage).
Concordance between fetal and neonatal measurements were evaluated using Lin's correlation coefficient [18, 19] and the Bland-Altman method [20, 21]. Data obtained from the ultrasonographic measurement of the upper arm was compared with the value obtained by the sum of biceps and triceps skinfold thicknesses [22]. Data obtained from the ultrasonographic measurement of the abdomen was compared with suprailiac skinfold thickness, and data obtained from the ultrasonographic measurement of the subscapular region was compared with subscapular skinfold thickness.
Statistical significance was set at 0.05 level. Statistical analyses were performed using Stata, Version 11 [23].
