Background: Belimumab (BEL) is a monoclonal antibody approved for SLE treatment but few data are available about its use before or during pregnancy.

Objectives: Our study aims to describe pregnancies in SLE patients who have discontinued BEL before conception, at positive pregnancy test or during pregnancy.

Methods: Data from prospectively-followed pregnancies (2014-2020) in SLE patients treated with BEL in 3 Italian centers where retrospectively collected, focusing on maternal disease activity, obstetric and neonatal outcome. Continuous data are expressed as median [min-max].

Results: Thirteen SLE pregnancies were analyzed (median age at conception 32 [24-41] years; 77% spontaneous, 69% primigravidae). All patients had positive ANA and anti-dsDNA antibodies; 4 had anti-Ro antibodies (31%); 4 had anti-phospholipid antibodies (aPL; 1 single, 2 double and 1 triple positivity). Seven patients (54%) had a history of lupus nephritis (LN); 2 patients (15%) had a concomitant diagnosis of antiphospholipid syndrome (1 thrombotic-APS and 1 thrombotic+obstetric-APS).

Ten (77%) pregnancies were planned and the use of BEL with regard to pregnancy was agreed with the patient during preconception counseling. At preconception visit, 8 patients were in remission while 5 had active disease (median SLEDAI 3 [0-8]).

BEL (11 intravenous, 2 subcutaneous) was stopped in 2 cases before conception, in 7 at positive pregnancy test and in 4 during pregnancy (2 at 11 ^th week, 1 at 22 ^nd , 1 at 24 ^th ); median duration of treatment at discontinuation was 29 [4-68] months. Other treatments during pregnancy were: oral prednisone in 12 cases (92%); intravenous methylprednisolone in 1 (8%); hydroxychloroquine in 10 (77%); chloroquine in 1 (8%); azathioprine in 5 (39%); calcineurin inhibitors in 5 (39%); low-dose acetylsalicylic acid in 10 (77%); low molecular weight heparin in 9 (69%).

Three flares occurred during the 3 ^rd trimester in patients who stopped BEL at positive pregnancy test.

Live-births occurred in 92% of the pregnancies. A patient with thrombotic+obstetric-APS and LN, underwent assisted reproductive technology (embryo donation) and developed eclampsia (25 ^th week), an urgent cesarean section was performed and the newborn died after 3 days. One pre-eclampsia occurred in a patient with history of LN, double aPL positivity and active disease. One miscarriage at 11 ^th week occurred; no early miscarriages (<10 ^th week) were recorded. Pregnancy complications and outcomes are reported in Table 1 .

No malformations were recorded. Two newborns were transferred to the Intensive Care Unit (1 for milk protein intolerance and 1 for desaturation).

Eight newborns received vaccinations according to national schedule (missing data for 3). Five newborns were breastfed, 1 received formula milk and 5 mixed-feeding. BEL was resumed in 7/13 patients after pregnancy (in 4 cases for flare), after a median period of 5 [4-22] months.

Conclusion: While more data are needed, this small series suggests that BEL might be a therapeutic option for SLE patients during pregnancy planning, similarly to other biological drugs used in chronic forms of arthritis.

Disclosure of Interests: None declared