In this study, researchers will learn more about the effects of diroximel fumarate (DRF), also known as VUMERITY®, when taken during pregnancy in people with multiple sclerosis, also known as MS. In MS, the immune system attacks the nerves in the brain and spinal cord. The affected areas are called lesions. The damage makes it difficult for the brain and spinal cord to function and send messages throughout the body. MS can be a progressive disease, which means it may get worse over time. In relapsing forms of MS (RMS), new symptoms may happen, and existing symptoms may get better or worse over time. DRF is an approved drug that is used to treat people with RMS.

This is known as an "observational" study, which collects health information about study participants without changing their medical care. The main goal of this study is to collect birth and health information from 3 groups of participants and their babies. These groups are:

• Those who took DRF during their pregnancy
• Those who took disease-modifying therapies (DMTs) for RMS during their pregnancy, but not DRF. DMTs are drugs that slow how the disease develops over time, not just relieve symptoms.
• Those who did not take any drugs for RMS during their pregnancy

The main question researchers want to learn about in this study is:

• How many participants' babies were born with major congenital malformations (MCMs)? MCMs are problems with how a baby's body forms before birth.

In this study, researchers will measure how often the following outcomes happen and compare them between groups:

• Loss of pregnancy before 20 weeks
• Loss of pregnancy at or after 20 weeks (stillbirth)
• Babies born early (before 37 weeks)
• Babies who are smaller than expected for the stage of pregnancy
• Live births

This study will be done as follows:

• The study includes data in adult women with multiple sclerosis on pregnancies happening between October 29th, 2019 and July 31st, 2030. Information will start being collected when the participant decides to join the study.
• Medical records and clinical notes will be reviewed at the end of the study.
• The study will include information from pregnancy through delivery, and for babies up to 1 year after birth.
• The study is planned to end by 30th April 2031.

The primary objective of the study is to estimate the prevalence of major congenital malformations (MCMs) and compare the prevalence between the diroximel fumarate (DRF) and comparator groups. The secondary objectives of the study are to estimate the incidence of spontaneous abortion (SA) and compare the incidence between the DRF and comparator groups; to estimate the incidence of preterm birth and compare the incidence between the DRF and comparator groups; to estimate the incidence of stillbirth and compare the incidence between the DRF and comparator groups; to estimate the prevalence of small for gestational age (SGA) and compare the prevalence between the DRF and comparator groups; and to estimate the incidence of live birth and compare the incidence between the DRF and comparator groups.

Key Inclusion Criteria:

• Last menstrual period (LMP) between 29 October 2019 and 31 July 2030.
• Continuous medical Optum Research Database (ORD) and pharmacy (ORD and Market Clarity) coverage for a minimum of 6 months prior to and including the estimated LMP.
• Presence of MS.

Key Exclusion Criteria:

- Pregnancies will be excluded from this study if they are exposed to any known teratogens from the beginning of baseline through the end of the relevant exposure window.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.

The participants included in this study will be drawn from the population of adult women with MS who become pregnant between 29 October 2019 and 31 July 2030.

In accordance with Biogen's Clinical Trial Transparency and Data Sharing Policy on https://www.biogentrialtransparency.com/