Background: Pregnancy complications of antiphospholipid syndrome (APS) are up to 20–30%. It is of great value to identify well-recognized predictors of adverse pregnancy outcomes (APOs) in APS. This study aims to explore the risk factors for APOs in patients with obstetric APS. Methods: This study included 142 women with APS delivered at Peking University People’s Hospital from February 2014 to August 2022. APOs included fetal death, neonatal death due to complications related to prematurity, preterm delivery 37 weeks due to placental insufficiency, hypertension, or preeclampsia, and small for gestational age (SGA) 10%. The association between pregnancy outcomes and clinical variables was assessed and the risk factors for APOs were analyzed. Results: APO occurred in 42.7% of pregnancies, including preterm delivery (23.4%), SGA (18.5%), and fetal death (6.5%). Patients in the APO group showed a significantly higher prevalence of underlying autoimmune disease (17% vs. 4.2%, p = 0.017) and lupus anticoagulant (LA) positivity (41.5% vs. 23.9%, p = 0.037) than those without APO. A significantly lower proportion of patients in the APO group were treated with low molecular weight heparin (LMWH) (58.5% vs. 76.1%, p = 0.037) and LMWH + low dose aspirin (LDA) (34.0% vs. 54.9%, p = 0.020) than in the non-APO group. Underlying autoimmune disease (odds ratio (OR): 5.147, 95% confidence interval (95% CI): 1.049–25.254, p = 0.043) was a risk factor for APOs and regular outpatient follow-up at the Department of Rheumatology and Immunology (OR: 0.429, 95% CI: 0.190–0.967, p = 0.041) was a protective factor for APOs. Conclusions: Underlying autoimmune disease is a risk factor for APOs and regular outpatient follow-up at the Department of Rheumatology and Immunology could be a protective factor for APOs.