Associations between gestational weight gain and birthweight outcomes for women with systemic lupus erythematosus: based on a single-center retrospective cohort study

To characterize gestational weight gain (GWG) in pregnant women with systemic lupus erythematosus (SLE) and analyze its association with neonatal birth weight. This retrospective cohort study included singleton pregnancies with SLE delivered at Peking Union Medical College Hospital (PUMCH) between June 2020 and September 2025, all of whom were definitively diagnosed by the Department of Rheumatology and Clinical Immunology. Each SLE case was matched 1:2 with non-SLE controls by age, prepregnancy body mass index, and parity. GWG patterns were described using Chinese standards. Factors associated with weight gain were analyzed using chi-square and nonparametric tests. Multivariate logistic regression models assessed associations between GWG and birthweight outcomes. A total of 160 SLE pregnancies and 320 controls were included. In the SLE group, 30.6%, 43.8%, and 25.6% had total GWG below, within, and above Chinese standards, respectively; for mid-late gestational weight gain rate (GWGR), the proportions were 15.0%, 41.9%, and 43.1%. Compared with controls, SLE pregnancies had a higher prevalence of both total GWG and mid-late GWGR falling below the Chinese standards (P 0.05). The incidences of full-term low birth weight (LBW) and small for gestational age (SGA) were 7.5% and 17.5%, whereas macrosomia and large for gestational age (LGA) were rare (0.6% and 3.8%, respectively). Multivariate logistic regression adjustment for confounding factors showed that a slow mid-late GWGR (< P25) significantly increased the risk of full-term LBW compared to an appropriate GWGR (P25-P75) adjusted odds ratio (aOR) = 6.560, 95% CI: 1.53–28.12, P = 0.011. Pregnant women with SLE exhibit a distinct weight gain pattern characterized by a high rate of inadequate total GWG and GWGR. Oral glucocorticoids did not contribute to additional weight gain. Notably, slow mid-late GWGR was associated with an increased risk of full-term LBW. In clinical practice, improved monitoring, risk assessment, and management of pregnant women with inadequate gestational weight gain are warranted.