Inclusion Criteria:

• Women between the age of 18-45 Groups A and B have to be confirmed pregnant by blood test (confirmed by medical records) Subgroups A1 and B1 are pregnant women in their first trimester Subgroups A2 and B2 are pregnant women in their second trimester Subgroups A3 and B3 are pregnant women in their third trimester

Exclusion Criteria:

• History of smoking or drinking during the pregnancy History of chronic diseases (cardiac, kidney, diabetes, hypertension, IBD,etc). Laxative use within 2 days prior to sample collection (The participant will be informed of the collection procedure by the recruiter and will be made aware of this requirement, we will also confirm when the first sample is taken through a phone call if for any reason the participant still made a mistake, will ask her to collect another sample to replace it) Development of any serious pregnancy complication during the participation period (e.g preeclampsia, preterm birth, miscarriage, etc) Excessive vomiting, diarrhea, or gastrointestinal symptoms for more than 5 consecutive days during the participation period. This will be confirmed through a weekly check-up call by the on-site recruiter or by Dr.Yin if the patient seeks treatment