Chronic hypertension is one of the major risk factors for preeclampsia. Pregnancy-specific beta-1-glycoprotein (PSG-1) is a protein that plays a critical role in fetomaternal immune modulation and has been shown to be closely associated with pregnancy adverse events such as preeclampsia. It is also known that PSG-1 and its source placenta are associated with many molecular pathways associated with blood pressure regulation. In addition, the nondipping pattern (NDP) of chronic hypertension has been shown to be an independent risk factor for preeclampsia. Dipper individuals experience a notable nighttime drop in blood pressure, typically around 10% or more compared to daytime levels, while nondipper individuals show a smaller nighttime blood pressure decrease, indicating potential circadian blood pressure regulation disruption. In this context, we aimed to reveal the relationship between PSG-1, NDP and preeclampsia in this study. A total of 304 pregnant women who were newly diagnosed in the first trimester and started on antihypertensive medication were included in this study. All subjects performed 24-h ambulatory blood pressure monitoring twice throughout pregnancy, the first in the 1. trimester to confirm the diagnosis of hypertension and the second between 20+0 and 21+1 gestational weeks to determine the dipper-nondipper status of hypertension. Subjects were grouped as dipper and nondipper according to blood pressure, and groups were compared in terms of PSG-1 levels. In this study, low PSG-1 levels and NDP were independently associated with preeclampsia. Findings from this study suggest that PSG-1 may play an important role in the causal relationship between NDP and preeclampsia.