Inclusion Criteria for healthy pregnant women:  Chinese mothers aged 18 - 45 years who were in the first trimester of pregnancy Singleton pregnancy Participate voluntarily and capable of giving informed consent  Inclusion Criteria for babies:  The baby of enrolled pregnant women and parents signed written informed consent prior to the initiation of this study.  Exclusion Criteria:  Significant medical conditions especially those required long term medications, such as oral steroid, antihypertensive drugs, diabetic medications and lipid-lowering agents, during or before pregnancy History of chronic inflammatory or neoplastic diseases involving the gastrointestinal tract (e.g. inflammatory bowel disease, coeliac disease, colorectal cancer) Significant pregnancy complications, such as intrauterine foetal demise/stillbirth, extreme prematurity, or pre-labour rupture of membranes before 24 weeks Mother with mental incapacity such that they are not able to give informed consent Foetal chromosomal or clinically significant structural abnormalities The current pregnancy is a conception through either sperm or ovum donation