Postmarketing Vedolizumab Milk-Only Lactation Study in Lactating Women With Active Ulcerative Colitis or Crohn's Disease

Inclusion Criteria: 1. Is capable of understanding and complying with protocol requirements. 2. Signs and dates as written, informed consent form and any required privacy authorization prior to the initiation of any study procedures. 3. Is female and at least 18 years of age at the time of informed consent. 4. A female participant of childbearing potential who is sexually active with a nonsterilized male partner agrees to use routinely adequate contraception from signing of informed consent and throughout the duration of the study. 5. Is on established vedolizumab maintenance therapy and received at least 1 dose of 300 mg of vedolizumab IV postpartum or has completed vedolizumab induction therapy (300 mg of vedolizumab IV at Week 0, Week 2, and Week 6), which has been commenced by the participant's treating physician for the treatment of active UC or CD prior to enrolling in this study. 6. Has delivered a single, normal term infant (at least 37 weeks' gestation) that is, a mother-infant pair is required. 7. Is at least 5 weeks postpartum by Day 1. 8. Lactation is well established, and the mother is exclusively breast feeding her infant (or not providing more than 1 supplemental bottle of formula/day) when enrolled in the study. 9. Participant has independently decided to be treated with vedolizumab or to breastfeed prior to providing consent to participate in this study. 10. Plans to continue breastfeeding at least throughout the duration of this study. 11. Agrees to use only the emollient or nipple cream recommended by the investigator for use during the sampling period. Exclusion Criteria: 1. Has received any investigational compound or approved biologic or biosimilar agent, except for vedolizumab within 60 days prior to enrollment in the study. 2. Within 30 days prior to enrollment, the participant has received any of the following for the treatment of underlying disease: * Nonbiologic therapies \[example (eg), cyclosporine\], other than those listed in the protocol. * An approved nonbiologic therapy in an investigational protocol. 3. Has received any live vaccinations within 30 days prior to vedolizumab administration. 4. Has clinically significant infection (eg, pneumonia, pyelonephritis) or chronic infection within 30 days prior to enrollment. 5. Is an immediate family member, study site employee, or is in a dependent relationship with a study site employee who is involved in the conduct of this study (eg, spouse, parent, child, sibling) or may consent under duress. 6. Has evidence of unstable or uncontrolled, clinically significant cardiovascular, central nervous system, pulmonary, hepatic, renal, gastrointestinal, genitourinary, hematological, coagulation, immunological, endocrine/metabolic or other medical disorder, including serious allergy, asthma, hypoxemia, hypertension, seizures or allergic skin rash that, in the opinion of the investigator, would confound the study results or compromise participant safety. Additionally, if there is any finding in the participant's medical history, physical examination, or safety laboratory tests giving reasonable suspicion of a disease that would contraindicate taking vedolizumab, or a similar drug that might interfere with the conduct of the study. 7. Had any surgical procedure requiring general anesthesia within 30 days prior to enrollment or is planning to undergo major surgery during the study period. 8. Has any history of malignancy, except for the following: (a) adequately treated nonmetastatic basal cell skin cancer; (b) squamous cell skin cancer that has been adequately treated and that has not recurred for at least 1 year prior to enrollment; and (c) history of cervical carcinoma in situ that has been adequately treated and that has not recurred for at least 3 years prior to enrollment. Participants with remote history of malignancy (eg, greater than (\>) 10 years since completion of curative therapy without recurrence) will be considered based on the nature of the malignancy and the therapy received and must be discussed with the sponsor on a case-by-case basis prior to enrollment. 9. Has a history of any major neurological disorders, including stroke, multiple sclerosis, brain tumor, or neurodegenerative disease. 10. Has a positive progressive multifocal leukoencephalopathy subjective symptom checklist at screening. 11. Has a current or recent history (within 1 year prior to enrollment) of alcohol dependence or illicit drug use. 12. Has active psychiatric problems that, in the investigator's opinion, may interfere with compliance with the study procedures. 13. Is unable to participate in all the study visits or comply with study procedures. 14. Has history of breast implants, breast augmentation, or breast reduction surgery. 15. Has a prior history of difficulty establishing lactation. 16. Has taken any excluded medication, supplements, or food products during the time periods listed in the Excluded Medications and Dietary Products table. 17. Has donated or lost 450 milliliters or more of her blood volume (including plasmapheresis), or had a transfusion of any blood product within 45 days prior to Day 1.