Single-Center Study Provides Support for Natalizumab Use in Pregnant Women With Multiple Sclerosis

Katrina Bawden, FNP-C

Findings from a single-center trial revealed that natalizumab (Tysabri; Biogen) use during pregnancy was associated with an absence of multiple sclerosis (MS) disease activity whereas those who discontinued treatment experienced increased clinical and/or MRI activity. Further research is needed to extend these data, particularly with respect to neonatal/infant outcomes.¹

Presented at the 2025 Consortium of Multiple Sclerosis Centers (CMSC) Annual Meeting, held May 28-31, in Phoenix, Arizona, the analysis included 43 women with MS representing 58 pregnancies. Of these pregnancies, 20 were on natalizumab until 34 weeks gestation or delivery and 38 had discontinued natalizumab at the time of a positive pregnancy test or within 8 weeks of conception. Conducted at the Rocky Mountain MS Clinic, in Colorado, the age at onset of pregnancy ranged from 21 to 41 years (mean, 29.8 years).

Led by Katrina Bawden, FNP-C, a board certified family nurse practitioner at Rocky Mountain MS Clinic, there were no observed MRI activity or relapses reported among the 20 patients who continued natalizumab through pregnancy. Among those who discontinued, 17 women showed MRI activity, 13 of which also had a clinical relapse. Of note, 8 of these women restarted natalizumab treatment during pregnancy.

Natalizumab exposure prior to pregnancy ranged from 0 to 163 doses (mean, 39.8), with 1 to 8 doses (mean, 2.37) administered during pregnancy. Within 3 months postpartum, a total of 18 relapses occurred, 17 of which were observed in women who discontinued natalizumab. Among the 31 women who restarted the treatment within 3 months postpartum, the average time to restart was 2 weeks (range, 1 day to 12 weeks).

READ MORE: Two-Year CHIMES Study Data Highlight Effect of Ocrelizumab in Diverse Relapsing MS Patient Population

Conducted between 2008 to 2024, investigators also had outcome data for 52 of the 58 pregnancies captured in the study. Of these, 36 were healthy live births, 10 miscarriages, and 6 abnormal neonatal outcomes. Furthermore, 26 women breastfed, while 13 opted not to breastfeed with the remainder unknown.

There have been several other studies examining natalizumab use during pregnancy in women with MS since its approval in 2004. In 2024, a prospective cohort study analyzed 350 pregnancies exposed to natalizumab, with findings that showed continuing natalizumab beyond the first trimester significantly reduced maternal relapse rates during pregnancy and postpartum. Published in Neurology, Neurosurgery, and Psychiatry, the study compared clinical disease activity and neonatal outcomes among women with natalizumab discontinuation during (1^st Trim-group) vs after the first trimester (maintaining-group) and for subgroup analysis before (<30-subgroup) or after (≥30-subgroup) the 30^th gestational week.²

In addition to showing fewer relapses during pregnancy and the postpartum year, women in the ≥30-subgroup had a significantly lower relapse risk in the first 6 months postpartum (relapse rate ratio, 0.36; 95% CI, 0.15-0.84). In total, 7.5% retained meaningful disability 12 months postpartum. Furthermore, no significant effect on neonatal outcomes was observed, but anemia (OR, 2.62; 95% CI, 1.12-6.52) and thrombocytopenia (OR, 2.64; 95% CI, 1.15-6.46) were significantly more common in the ≥30-subgroup. Of note, 21.8% of all neonates were born small for gestational age, independent of the timing of natalizumab discontinuation.

Another 2022 study based in Italy also confirmed natalizumab’s beneficial effects on the risk of clinical and radiological reactivation in pregnant patients with MS. The study, published in Neurology, Neurosurgery, and Psychiatry, comprised 170 eligible pregnancies from 163 women referring to 29 Italian centers. Overall, delaying natalizumab resumption after delivery significantly increased the risk of relapses (OR, 1.29; 95% CI, 1.07-1.57; P = .0009) and gadolinium-enhancing lesions (OR, 1.49; 95% CI, 1.17-1.89; P = .001).³

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REFERENCES
1. Bawden K, Riddle E, Menning K, Rutledge D, Christensen A, Foley J. LBA12 - Pregnancy and Natalizumab: A Single US Center Experience of 58 Pregnancies. Presented at: 2025 CMSC Annual Meeting; May 28-31. Phoenix, AZ. LBA12.
2. Thiel S, Litvin N, Haben S, Gold R, Hellwig K. Disease activity and neonatal outcomes after exposure to natalizumab throughout pregnancy. J Neurol Neurosurg Psychiatry. 2024;95(6):561-570. doi:10.1136/jnnp-2023-332804.
3. Landi D, Bovis F, Grimaldi A, et al. Exposure to natalizumab throughout pregnancy: effectiveness and safety in an Italian cohort of women with multiple sclerosis. J Neurol Neurosurg Psychiatry. 2022;329657. doi:10.1136/jnnp-2022-329657