Treatment with natalizumab during pregnancy in multiple sclerosis: The experience of implementing a clinical practice...

Pregnancy planning in women with highly active multiple sclerosis (HAMS) who need a high-efficacy disease-modifying therapy (heDMT) currently requires a careful risk-benefit evaluation. This includes minimizing fetal drug toxicity and preventing MS reactivation. We describe our experience with natalizumab in women with HAMS and unplanned pregnancy by implementing a clinical practice protocol (NAP-30) designed to maintain the effectiveness of natalizumab during pregnancy, reduce fetal exposure and prevent complications.

This was an observational retrospective study including women with HAMS on active treatment with natalizumab who became unexpectedly pregnant in the period 2018-2021 and continued this treatment during pregnancy according to the NAP-30 protocol. MS clinical and radiological variables were analyzed before and during pregnancy and in the postpartum period, along with maternal and fetal toxicity during pregnancy and safety findings in newborns. We also describe the NAP-30 protocol, which includes the use of a bridging dose to adjust and maintain natalizumab infusions every 6 weeks during pregnancy up to week 30 and scheduled delivery at week 40.

Six women (one in her first gestation) with a median age of 31.5 years at the onset of pregnancy (min-max: 24-37 years) were included. All were negative for anti-John Cunningham virus (JCV) antibodies and were on treatment with intravenous natalizumab 300 mg every 4 weeks. At the time of conception, three patients had received 12, 17 and 53 infusions of natalizumab, respectively, while for the remaining three patients natalizumab was their first DMT (two patients had received 6 infusions and one patient had received 3 infusions of natalizumab). All six patients received 6 doses of natalizumab during pregnancy according to the NAP-30 protocol. After delivery, all six patients restarted natalizumab every 4 weeks (median: 3 days; range: 2-4 days). No patients had relapses during pregnancy or at 6 months postpartum, nor did they develop any general health or laboratory abnormalities. The MRI scan performed at 4-6 months postpartum showed no new T2 lesions or gadolinium-enhancing lesions. No miscarriages or threatened miscarriages were reported. One of the patients underwent elective preterm delivery at week 35 after mild-to-moderate anemia was detected by fetal Doppler scan. The newborn had low birth weight (2080 g) and mild anemia, which resolved within two months with oral iron supplementation. The other infants were born with normal birth weight and showed no blood count abnormalities. After a median follow-up of 10 months, all six babies showed normal development with no complications detected.

Based on our experience, the implementation of the NAP-30 protocol in women with HAMS and unplanned pregnancy undergoing treatment with natalizumab allows the continuation of natalizumab during pregnancy, with a very favorable clinical and radiological effectiveness and maternal-fetal safety profile during pregnancy and postpartum. Both in pregnancy with HAMS and in general, and particularly for successful implementation of the NAP-30 protocol, obstetric support and monitoring is essential for adequate pregnancy management.