Objective: To assess the influences of pregnancy on disease progression of neuromyelitis optica spectrum disorders (NMOSD) and multiple sclerosis (MS). Methods: A total of 148 NMOSD patients and 170 MS patients were reviewed retrospectively. The changes in mean annualized relapse rate (ARR) in NMOSD and MS during and after pregnancy were compared. The influences of different pregnancy outcomes on disease courses were also analyzed. Results: Sixty-two relapses had occurred during pregnancy or within 1 year after delivery/abortion in NMOSD patients and 64 in MS patients. The proportion of pregnancy-related onset and relapse in NMOSD was not significantly higher than that in MS. The ARR during 0-3 months and 7-9 months postpartum/postabortal periods in NMOSD and during 0-3 months and 10-12 months postpartum/postabortal periods in MS increased significantly. The ARR in 7-9 months postpartum/postabortal period in NMOSD patients was significantly higher than that in MS patients. Different pregnancy outcomes affected the course of disease similarly in patients irrespective of NMOSD or MS. Conclusions: Both NMOSD and MS presented increased onset and relapses after delivery/abortion. Significant differences were observed in ARRs at different stages between them. Both delivery and abortion exerted detrimental effects on disease courses in NMOSD and MS.