Pregnancy Exposure Registry for Tysabri®

Key Inclusion Criteria: Females who become pregnant while they are taking TYSABRI® as part of the TYGRIS program, during a clinical trial with TYSABRI® that is sponsored by Biogen-Idec, or in the post-marketing setting may enroll in this Registry, as follows: 1. Documentation that the patient was exposed to TYSABRI® within 90 days prior to first day of Last Menstrual Period (LMP) or during pregnancy. (If exposure dates are unknown, the reporter must be able to specify or estimate trimester of exposure). 2. The outcome of the pregnancy must not be known at the time of enrollment. For pregnancies for which the outcomes are known at the time of enrollment, the information will be collected as retrospective reports and analyzed separately. 3. For US patients, verbal informed consent must be collected at the time of enrollment. The Coordinating Center (CC) obtains verbal informed consent (if verbal consent has not already been obtained by the physician). The CC then mails the patient a Release of Medical Information form to sign and return. If the patient is a minor, verbal consent must be obtained from the parent or legal guardian and verbal assent must be obtained from the patient. 4. For Canadian patients, a written informed consent must be collected by the TYGRIS investigator at the time of enrollment. A Release of Medical Information form will also be signed by the patient and returned to the CC. NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.