The aim of this study was to investigate the relationship between the maternal serum levels of pregnancy-specific beta-1-glycoprotein 1 (PSG1) and preeclampsia, and to compare levels of PSG1 in pregnancies with preeclampsia and uneventful pregnancies. A case-control study was conducted in a research and training hospital. A total of 40 women with preeclampsia and 42 healthy pregnant women who were gestational age-matched were included. Serum PSG1 levels were measured using enzyme-linked immunosorbent assay. The maternal serum PSG1 levels were significantly lower in patients with preeclampsia compared with controls (11.60 +/- 8.08 vs. 17.58 +/- 9.72 ng/mL, p = .003). Circulating PSG1 levels were negatively correlated with age in the preeclampsia and control groups (r = -0.322, p = .043), (r = -0.430, p = .005). PSG1 levels, age, blood urea nitrogen levels and birth weight were significantly associated with high odds of having preeclampsia. Receiver operating characteristic (ROC) curve analysis confirmed that the area under ROC curve was 0.707 (95% CI: [0.595-0.819], p < .001) for PSG1. The optimal cut-off value of PSG1 for detecting preeclampsia was <= 11.80 ng/mL. There may be a decrease in PSG1 production in preeclampsia-complicated pregnancies where there are pathologies related to placenta formation. A decline in PSG1 concentrations may reflect placental dysfunction.Impact Statement What is already known on this subject? Previous studies have reported abnormal pregnancy-specific glycoprotein (PSG) levels in complicated pregnancies and demonstrated their importance in maintaining a healthy pregnancy. Human PSG homologues have been identified in species with haemochorial placentation such as non-human primates, rats and mice, where foetal cells are in direct contact with the maternal circulation. There are studies in which there is no clear relationship between PSGs and preeclampsia. What the results of this study add? We have demonstrated that circulating PSG1 levels were significantly lower in women with preeclampsia than in healthy pregnant women. There may be a decrease in PSG1 production in preeclampsia-complicated pregnancies where there are pathologies related to placenta formation and function. The results obtained from this current study could be used to clarify the relationship between PSG1 levels and preeclampsia.