This is a cohort study to understand the changes of breastmilk composition in the first six months after birth of Chinese infants.

The relationship of breastmilk composition, the maternal gut microbiome and lifestyle factors such as diet, feeding practices and physical activity and the infant's health and gut microbiome will be investigated in this study.

Inclusion Criteria:

Mothers:

1. Generally healthy mothers with the intention to breastfeed.
2. Aged 18 years and above.
3. Written informed consent.

Infants:

1. Generally healthy term born (gestational age between 37 and 42 weeks).
2. Breastfed by their mothers, either exclusively or in combination with infant milk formula, at enrolment.
3. Chinese ethnicity of mother and father.

Exclusion Criteria:

Mothers:

1. Participation in any other studies involving investigational or marketed products concomitantly or two weeks prior to entry into the study.
2. Difficulty to follow up and/or locate (e.g. known transfer to other hospitals, residing outside the city where the study site is located, or planning to move out of the current city; incapability of mothers to comply with study protocol or investigator' s uncertainty about the willingness or ability of the mothers to understand and comply with the protocol requirements.
3. Illegal drug use.
4. Regular smoking and/ or consumption of alcoholic beverages as per investigator's judgement.
5. A BMI of <18.5 or ≥ 28 pre-pregnancy or during the first regular pregnancy check around or before 16 weeks of gestational age.
6. Acute infectious disease or neoplastic disease or any kind of weakening or debilitating conditions (with history of positive, hepatitis C virus (HCV) or HIV serological test at any time during the pregnancy).
7. Presence of mastitis, fungal infections of the nipple or areola; reactivation of herpes simplex (HSV) or varicella zoster infection in the mammary or thoracic region at the time of enrolment.
8. Presence of chronic diseases such as endocrine, cardiovascular, renal, respiratory or hepatic diseases.
9. Presence of psychosis and severe post-partum depression.
10. Presence of autoimmune disease such as systemic lupus erythematosus, systemic scleroderma, ulcerative colitis, Crohn's disease, celiac disease.
11. Women whose health condition, according to the investigator's judgement, could interfere with the study conduction and assessment.
12. Mothers who have given birth to twins or multiples or infant conceived with Assisted Reproductive Technology (ART).

Infants:

1. Participation in any other studies involving investigational or marketed products concomitantly or two weeks prior to entry into the study.
2. At enrolment, any congenital abnormality, chromosomal disorder or severe disease which could interfere with the study conduct and assessment.
3. Consumption of food other than breast milk or infant formula.
4. Fully formula fed at enrolment.

Generally healthy mothers with the intention to breastfeed, and their infants.