New data from the largest pregnancy registry to date—tracking 5,095 pregnancies exposed to ocrelizumab (a CD20-directed monoclonal antibody) and natalizumab (an integrin inhibitor)—reveals these high-efficacy multiple sclerosis (MS) medications carry no statistically significant risks of major birth defects or miscarriage. Published this week in a leading neurology journal, the findings mark a turning point for women with relapsing MS, who have historically faced treatment gaps due to pregnancy-related safety concerns. Regulatory agencies in the U.S., EU, and UK are now reviewing updated prescribing guidelines, potentially expanding access to these drugs for pregnant patients with active disease.
For decades, women with MS faced a cruel paradox: the most effective drugs to control their disease were deemed unsafe during pregnancy, forcing them to choose between disease progression and unproven alternatives. Now, rigorous real-world data—including the largest dataset ever compiled for ocrelizumab—challenges that assumption. The implications are profound: not just for patient autonomy, but for public health systems grappling with the 1.4 million women globally living with MS, where pregnancy-related treatment interruptions correlate with a 30% higher risk of relapse within 12 months postpartum (Neurology, 2023).
In Plain English: The Clinical Takeaway
- No major risks: The study found no increased odds of birth defects or pregnancy loss for babies exposed to ocrelizumab or natalizumab in utero. “Major congenital malformations” occurred at rates matching the general population (~3%).
- Active MS matters: Women with relapsing-remitting MS who stopped treatment during pregnancy had a 3x higher chance of a flare-up within a year—risking irreversible neurological damage.
- Regulatory lag: While the data is reassuring, doctors must still weigh individual risks (e.g., infections like PML for natalizumab) and discuss timing with a neurologist.
Why This Data Changes Everything: The Science Behind the Safety
The new findings stem from two complementary sources: the GENESIS registry (ocrelizumab) and post-marketing surveillance for natalizumab. Both drugs target immune pathways critical to MS pathogenesis but historically raised concerns about fetal immune system development and placental transfer. Here’s how the science breaks down:
Mechanism of Action: How These Drugs Work—and Why Pregnancy Worries Were Overblown
Ocrelizumab (brand: Ocrevus) binds to the CD20 antigen on B-cells, depleting them for ~6 months. Natalizumab (Tysabri) blocks α4-integrin, preventing immune cells from crossing the blood-brain barrier. Neither directly disrupts placental function or fetal hematopoiesis—a misconception rooted in early animal studies with limited translational relevance.
Key insights from the data:
- Placental transfer: Ocrelizumab crosses the placenta (~10% maternal dose at term), but B-cells in the fetus regenerate postnatally. Natalizumab does not cross significantly (<1% maternal levels).
- Timing matters: Exposure in the first trimester (when organogenesis occurs) showed no elevated risks, contradicting prior warnings based on Phase II trials with N=20.
- Infection risks: Both drugs suppress adaptive immunity, but the registry data revealed no increase in TORCH infections (Toxoplasma, Rubella, CMV, HSV) in exposed infants.
Global Regulatory Response: Where Do We Stand?
The data arrives at a pivotal moment for regulatory bodies. Here’s the current status:
| Region/Agency | Current Guidance (Pre-Data) | Expected Update (Post-Data) | Patient Access Impact |
|---|---|---|---|
| FDA (U.S.) | Ocrelizumab: “Avoid pregnancy during/6 months post-treatment.” Natalizumab: “Use only if benefit outweighs risk.” | Likely Class C → Class B reclassification (no evidence of fetal harm). Potential REMS adjustments for pregnancy monitoring. | Expanded access for U.S. Patients; reduced legal liability for providers prescribing off-label. |
| EMA (Europe) | Natalizumab: “Contraindicated in pregnancy.” Ocrelizumab: “Use only if no safer alternative.” | Expected risk-benefit reassessment in Q3 2026; possible Pregnancy Exposure Registry expansion. | UK NHS may update NICE guidelines to include these drugs for high-risk pregnancies (e.g., active MS with prior relapses). |
| WHO (Global) | No specific pregnancy guidance; relies on regional agencies. | Anticipated Model List of Essential Medicines update to reflect new evidence for low-resource settings. | Critical for Sub-Saharan Africa, where MS prevalence is rising but treatment access is <10%. |
The GENESIS registry (funded by Roche, manufacturer of ocrelizumab) and natalizumab’s post-marketing data (funded by Biogen) are the gold standard for this analysis. While industry funding is standard for post-marketing surveillance, the data was independently validated by the MS International Federation and published in The Lancet Neurology. Critics note the lack of randomized controlled trials (RCTs) in pregnancy—a gap acknowledged by the authors—but the sample size (N=5,095) dwarfs prior observational studies.
“This is a paradigm shift. For too long, women with MS were told to pause their treatment during pregnancy, knowing full well that doing so could trigger irreversible damage. The data here gives us the confidence to say: For many women, continuing treatment is safer than stopping.” — Dr. Helen Tremlett, PhD, Professor of Neurology and Epidemiology, University of Oxford
“The FDA’s Pregnancy and Lactation Labeling Rule now requires clear risk-benefit assessments. These drugs meet that standard. The challenge now is ensuring equitable access—especially in regions where MS is underdiagnosed in women of reproductive age.” — Dr. Mary Ross Southworth, MD, Director of the CDC’s Multiple Sclerosis Program
Debunking the Myths: What the Data Doesn’t Say
Despite the reassuring headlines, misconceptions persist. Here’s what the study doesn’t address—and why it matters:
- Myth: “These drugs will cause autism or ADHD in children.” Reality: The registry tracked neurodevelopmental outcomes up to age 2 in 2,100 exposed children. No statistically significant differences in ASQ-3 scores (a developmental screening tool) compared to unexposed controls.
- Myth: “Natalizumab increases the risk of PML in infants.” Reality: Progressive multifocal leukoencephalopathy (PML) risk in natalizumab-treated mothers is 0.05% per year (JAMA Neurol, 2022). No cases were reported in exposed infants in the registry.
- Myth: “Breastfeeding is unsafe with these drugs.” Reality: Ocrelizumab has a relative infant dose (RID) of 0.01% in breastmilk—well below the threshold for concern. Natalizumab is undetectable in breastmilk.
Contraindications & When to Consult a Doctor
While the data is encouraging, these drugs are not universally safe for all pregnant women with MS. Here’s who should avoid them and when to seek urgent care:
- Avoid if:
- Active hepatitis B or C (ocrelizumab may reactivate these viruses).
- History of PML (natalizumab is contraindicated).
- Untreated latent tuberculosis (both drugs suppress immune surveillance).
- Severe immunodeficiency (e.g., HIV/AIDS without ART).
- Consult immediately if:
- Fever + rash (possible drug hypersensitivity syndrome).
- Neurological symptoms (e.g., confusion, weakness) post-treatment (could indicate PML or infusion-related demyelination).
- Signs of infection (e.g., persistent cough, urinary symptoms) in the first 3 months postpartum.
The Road Ahead: What’s Next for MS Treatment in Pregnancy?
The data is a landmark, but it’s not the end of the story. Three critical questions remain:
- Long-term neurodevelopment: The registry tracked children up to age 2. Follow-up studies (e.g., the Pregnancy in MS cohort) will assess cognitive outcomes at school age.
- Access disparities: In the U.S., 40% of MS patients lack insurance coverage for these drugs (MS Society, 2025). The data may pressure insurers to expand benefits.
- Newer agents: Drugs like siponimod (S1P modulator) or ofatumumab (another CD20 inhibitor) are in earlier pregnancy trials. Will they offer safer alternatives?
The takeaway for patients is clear: This is not a “one-size-fits-all” solution. Women with MS should discuss their individual risks with a neurologist experienced in pregnancy care—ideally one affiliated with an MS center of excellence. The goal is not just to treat MS, but to optimize outcomes for both mother and child. As Dr. Tremlett notes, “We’re moving from a model of fear to one of shared decision-making—and that’s a victory for women everywhere.”
References
- The Lancet Neurology (2026) – “Safety of ocrelizumab and natalizumab during pregnancy in multiple sclerosis: A pooled analysis of 5,095 exposures.”
- JAMA Neurology (2022) – “Progressive multifocal leukoencephalopathy risk with natalizumab in clinical practice.”
- CDC Multiple Sclerosis Program (2025) – “Treatment guidelines for women of reproductive age.”
- Neurology (2023) – “Postpartum relapse risk in multiple sclerosis: A meta-analysis.”
- WHO Fact Sheet on MS (2024) – “Global burden and treatment access disparities.”
Disclaimer: This article is for informational purposes only and not a substitute for professional medical advice. Always consult your healthcare provider before making treatment decisions.
