We consecutively enrolled 20 SGA infants, born at term (37+0/41+3 week gestation), aged 24 months, and 20 AGA, age- and sex-matched controls. SGA was defined as a birth weight \<10th percentile for sex, gestational age and birth order, and AGA as a birth weight between the 10th and the 90th percentile, according to Italian neonatal anthropometric charts.
Clinical and anthropometric variables The infants' prenatal and neonatal data were retrospectively recorded, namely a history of gestational diabetes and hypertension, the presence of intrauterine growth restriction, maternal weight gain during pregnancy, Apgar score, gestational age and birth weight, length, and head circumference. All subjects' parents completed a questionnaire including family history, maternal smoking during pregnancy, breastfeeding duration. At the time of enrollment (24 months), anthropometric data were evaluated by trained physicians according to standard procedures and based on the WHO growth charts. Height, weight, systolic (SBP) and diastolic (DBP) blood pressure were measured. Body mass index (BMI) was calculated as weight (kg)/height(cm)2 and weight gain in the first 2 years of life was calculated as the delta between birth weight and weight at 24 months.
Echocardiographic assessment Transthoracic echocardiogram using a Vivid 7 Pro ultrasound scanner (General Electric Healthcare, USA) was performed by an expert pediatric cardiologist, blinded to patients' clinical data. Measurements of left ventricle (LV end-diastolic diameter, LVEDD; LV end-systolic diameter, LVESD; interventricular septum at end diastole, IVSD; LV posterior wall at end diastole, LVPWD), relative wall thickness (RWT), left atrium diameter (LAD), the maximum LA volume, LV ejection fraction, and tricuspid annular plane systolic excursion (TAPSE) were obtained according to established standards. LV mass (LVM) was derived from the Devereux formula and indexed to body surface area (left ventricular mass index, LVMI). Left ventricular output (LVO) was obtained with the velocity time integral (VTI) from a 5-chamber view and calculated as follows LVO=\[(VTI)x(heart rate)x(cross-sectional area)\] and indexed to body weight.
Using pulsed wave Doppler, mitral inflow velocities, peak early diastolic velocity (E), peak late diastolic velocity (A), and E/A ratio, were measured. Pulsed wave tissue Doppler of the lateral mitral annulus was used for the measurement of early peak diastolic mitral annular velocity (E'). The E/E' ratio was calculated. End-diastolic pressure (EDP) was calculated from the E/E' ratio with the formula EDP=1.91+1.24xE/E' (14) and the pressure-volume curve during diastole with the formula EDP = αxEDVβ (end-diastolic volume, EDV). Volume parameters were corrected to fixed values of EDP (V30 mmHg). The coefficient "β" (Beta), indicating the slope of the end-diastolic pressure-volume relationship (EDPVR), was calculated with the formula β=\[Log10(EDP/30)\]/\[Log10(EDV/V30mmHg)\].
Vascular assessment Vascular measurements were performed with a high-resolution ultrasonography (Esaote MyLab25TM Gold, Esaote, Italy) using a 8 mHz linear transducer and a 5 mHz convex transducer for the abdominal aorta, by an expert vascular surgeon blinded to patients' clinical status. CIMT, abdominal aortic diameter at maximum systolic expansion (Ds) and minimum diastolic expansion (Dd), brachial artery diameters, brachial artery peak systolic velocity (PSV) and end diastolic velocity (EDV) were measured as previously described and aortic strain (S), pressure strain elastic modulus (Ep), pressure strain normalized by diastolic pressure (Ep\*) and brachial artery flow-mediated dilation (FMD) were calculated. While S is the mean strain of the aortic wall, Ep and Ep\* are the mean stiffness (16). Arterial wall stiffness index (β index) was calculated with the formula: β index=ln(SBP/DBP)/\[(Ds-Dd) /Dd)\] (17) and systemic vascular resistance (dynes/s/cm2) with the formula: SVR=(mean BP- right atrial pressure)/LVO, with an estimated right atrial pressure of 5 mmHg. The brachial artery maximum diameter recorded following reactive hyperemia was reported as a percentage change of resting diameter (FMD = peak diameter - baseline diameter/baseline diameter).
