Few studies have been published focusing on the clinical features of new-onset systemic lupus erythematosus (SLE) during pregnancy. This study examined the clinical characteristics of SLE during pregnancy or puerperium. The clinical characteristics and serological parameters of 48 patients with onset of SLE during pregnancy were retrospectively compared with those of age-matched new-onset SLE patients who were diagnosed in a period of more than 12 months without pregnancy (n = 65) and age-matched preeclampsia patients (n = 48). SLE tended to occur during the first and second trimesters (33 and 42 %, respectively). Lupus nephritis (LN) and severe thrombocytopenia were more commonly seen in new-onset SLE during pregnancy than in patients without pregnancy (68.8 vs 35.4 % and 25 vs 9.2 %, respectively, p < 0.05). However, pregnant patients had lower frequency of fever, arthritis, arthralgia, alopecia, oral ulcer, and hypocomplementemia than the nonpregnant controls (p < 0.05). Compared to LN patients without pregnancy (n = 23), LN patients with pregnancy (n = 33) had more prominent proteinuria and nephrotic syndrome (p < 0.05). On the other hand, when compared to patients with preeclampsia, patients with new-onset SLE during pregnancy had early onset of symptoms during gestation and were characterized by presence of fever, malar lesion, autoantibodies, hypocomplementemia, hyperuricemia, active urinary sediment, and multi-organ involvement. In conclusion, patients with their first onset of lupus during pregnancy generally have more severe disease with higher prevalence of renal and platelet involvement.