Statistical analysis
Descriptive data was expressed as median and interquartile range (IQR)
and in proportions (absolute and relative frequencies). Spearman
correlation coefficient (Rho) was calculated as a measure of the degree
of the relationship between each immunoglobulin type measured in
colostrum and maternal serum, and between each immunoglobulin type
measured in mature milk and maternal serum. Linear regression analysis
was performed to assess the relationship between maternal symptoms and
immunoglobulin levels. Coefficients, 95% confidence interval (CI) and
p-value were reported. To graphically represent the relationship between
antibody levels and time lapse to disease, we adjusted a locally
weighted scatterplot smoothing (LOWESS) regression which, essentially,
joins together the curves generated by several regressions derived from
different segments of the timeframe23.
Lastly, to see how each immunoglobulin type evolved from the colostrum
to the mature milk, paired t-test was used. This analysis was performed
separately for women with active disease and those who had recovered
from SARS-CoV-2 infection. In all cases mean of the differences, 95% CI
and p-value were reported. Level of significance was set up at 0·05.
The statistical software R version 4·0·3 (Vienna, Austria) was used for
all data analyses24.