Statistical analyses
Continuous variables were represented using mean, standard deviation, median, minimum, and maximum value while categorical ones using absolute and relative frequencies. Fasting and postprandial TSBA 2.5th and 97.5th percentiles and their 95% confidence intervals were reported.
In order to assess the association between fasting or postprandial TSBA and maternal and neonatal characteristics the Pearson’s correlation coefficient was used. To evaluate the difference in fasting or postprandial TSBA between groups a T-test, Satterthwaite T-test or Mann-Whitney test were used according to Shapiro-Wilk test and F-Test for normality and homoschedasticity respectively.
The Kruskal-Wallis test was used to assess the difference in fasting or postprandial TSBA between seasons, according to Shapiro-Wilk test for normality.
The statistical analyses were conducted using statistical software package SAS 9.3 and the significance level was set at 5%.

Ethical approval

This study was performed according to the principles of the Declaration of Helsinki and was approved by the ethics committee of Careggi University Hospital (reference number 18008_bio).