The goal of this observational study is to learn about the distribution of bioimpedance vector of healthy neonates in China in health conditions. The main question it aims to answer are:whether the distribution of bioimpedance vector of healthy neonates in China is correspond to that in other countries.Participants will be measures by NUTRILAB impedance analyzer (Akern, Florence, Italy).

Data such as demographic data, maternal background, gestational age at birth, gestational history, weight and height, will be collected from medical records.Each day we will measure 3 newborns chosen by simple random sampling, for which we will use Excel function.Bioimpedance analysis will be performed according to the manufacturer's instructions within the first 24 hours of life, using a tetrapolar configuration of electrodes (at 400 μA and 50 kHz) with a NUTRILAB impedance analyzer (Akern, Florence, Italy). BIA data will be acquired when they are still, preferably in quiet sleep, avoiding contact between the upper limbs and trunk, and between the legs. Two outer distal adhesive electrodes will be placed on the dorsal surface of the right hand and foot, proximal to the metacarpal-phalangeal and metatarsal-phalangeal joints, and 2 inner electrodes will be placed proximally on the right fore-arm and pretibial region, leaving 5.5cm of free skin around the outer electrodes. The surface should have no skin lesions and will be cleaned with chlorhexidine solution. R and Xc values will be measured in triplicate in each infant, and the arithmetic mean will be used. The device will be calibrated every 20 evaluations(approximately once a week) using a resistor provided by the manufacturer. All the measurements will be performed at the nursery by the same investigator.We will use BIVA to analyse the result: the components of the impedance vector (R and Xc) will be normalized by the height (R/H [ohm/m] and Xc/H [ohm/m], respectively). PA is obtained from the arc-tangent ratio Xc:R. To transform it from radians to degrees, the result is multiplied by 180°/π。Using the RXc graph method the bivariate 95% confidence intervals (ellipses) of the mean vectors of the newborns will be established. From the bivariate normal distribution of R/H and Xc/H, the bivariate 95%, 75%, and 50% tolerance intervals will be drawn. We will use the Hotelling T2 test and univariate analysis (F test) by the BIVA software 2002 for the analysis of the CI for the comparison of the subject groups and for the analysis of tolerance intervals. The significance level is set at 0.05 in all tests.

Inclusion Criteria:

1. Healthy term neonates of both sexes within 24 hours.
2. Neonates whose parents or guardians consent with the research.

Exclusion Criteria:

1. Infants with some disease and conditions that could interfere in the body composition (such as heart failure, blue light irradiation, sepsis, kidney injury, hepatic failure, transfusion) and newborns with congenital anomalies and/or genetic problems.
2. Neonates whose parents or guardians refuse to participate in the research.

Chinese healthy term newborns born within 24 hours.