Prospective reports will be collected from pregnant subjects, health care providers (HCPs), or Biogen Idec Drug Safety and Risk Management (DSRM) staff. Data from pregnant subjects will be collected at 4 to 5 months of pregnancy and 8 to 12 weeks after the estimated date of delivery (EDD) by telephone interviews with the Registry. The Registry will confirm the information collected from the subject with the HCP by telephone interviews with the Registry, paper forms mailed/faxed to the Registry, electronic forms/queries sent to the Registry, or a combination of these methods. If a live birth is reported, the infant's HCP will be contacted for the Pediatric Follow-Up at 8 to 12 weeks age. If a birth defect is reported, targeted follow-up will be conducted.

Pregnant women with MS who were exposed to Avonex in the US

Inclusion Criteria:

• Have been exposed to AVONEX® within approximately 1 week of conception or during the first trimester of pregnancy.
• Provide sufficient information to determine that the pregnancy is prospectively registered (i.e., the outcome of pregnancy must be unknown prospectively).
• Provide verbal consent to participate in the Registry.
• Verbally provide contact information for herself, her HCP, and the infant's HCP (if applicable).