This study aims for characterization of different maternal, infant and environmental factors (e.g. maternal age, pregnancy duration, lactation period, baby gender, circadian rhythm, Holder pasteurisation, etc.) that influence human milk composition.

The study consists of three parts. In the first part the investigators aim to evaluate human milk macronutrient composition depending on the time after delivery and pregnancy duration.

In the second part the investigators aim to evaluate the circadian variation of human milk macronutrient and energy content depending on pregnancy duration.

In the third part the investigators aim to evaluate the influence of Holder pasteurisation on human milk macronutrient, metabolome and bioactive protein (lysozyme and lactoferrin) content.

Inclusion Criteria:

having obtained informed consent; after a single-birth pregnancy; women who were not on a special diet; lactating mothers who could not breastfeed their newborns due to the baby's medical condition (either prematurity or disease) but who expressed milk.

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Exclusion Criteria:

breastfeeding mothers; history of maternal diabetes, hepatitis B or C, HIV, tuberculosis, mastitis, or oncological disease; drug addicted.

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Lactating women

Mothers of newborns admitted at Neonatal Center of Vilnius University Hospital Santaros Klinikos, Lithuania