Introduction: Rheumatoid arthritis (RA) improves during pregnancy and flares after delivery. It has been hypothesized that high levels of the complement factor mannose-binding lectin (MBL) are associated with a favourable disease course of RA by facilitating the clearance of pathogenic immunoglobulin G (IgG) lacking galactose sugar moieties. During pregnancy, increased galactosylation of IgG and simultaneously increased MBL levels can be observed, with the latter being strictly related to maternal MBL genotypes. Therefore, increased MBL levels in concert with increased IgG galactosylation may be associated with pregnancy-induced improvement of RA. The objective of this study was to investigate whether MBL genotypes are associated with changes in RA disease activity and with changes in IgG galactosylation during pregnancy and in the postpartum period. We also studied the association between MBL genotypes and pregnancy outcomes in RA. Methods: Serum from 216 patients with RA and 31 healthy controls participating in the Pregnancy-induced Amelioration of Rheumatoid Arthritis (PARA) Study was collected before, during and after pregnancy. IgG galactosylation was determined by performing matrix-assisted laser desorption/ionization time of flight mass spectrometry. Disease activity was determined using the internationally recognized Disease Activity Score 28 (DAS28). MBL genotypes were determined. The pregnancy outcome measures studied were gestational age, birth weight, miscarriage and hypertensive disorders. Results: No association was found between the MBL genotype groups and changes in RA disease activity (P = 0.89) or changes in IgG galactosylation (patients, P = 0.75, and controls, P = 0.54) during pregnancy and in the postpartum period. Furthermore, MBL genotype groups were not related to the studied pregnancy outcome measures. Conclusions: This study does not provide evidence for a role for MBL in the improvement of RA during pregnancy or for a role for MBL in pregnancy outcome.