PSG3 (pregnancy specific beta-1-glycoprotein 3) is a member of the pregnancy-specific glycoprotein gene family located on chromosome 19.2 within a cluster of 11 PSG genes arranged in tandem orientation 1. The primary function of PSG3 relates to pregnancy maintenance and trophoblast differentiation. PSG3 expression is almost undetectable in undifferentiated trophoblast cells but becomes highly transcribed during cytotrophoblast differentiation into syncytiotrophoblast, serving as an early marker of this process 2. Transcriptional regulation involves a retinoic acid responsive element (RARE) and GA-binding protein (GABP) consensus site within its promoter region 2. Clinically, PSG3 demonstrates significant biomarker potential in reproductive health, showing utility in multiplexed prediction models for distinguishing viable from nonviable pregnancies and identifying ectopic pregnancies with high sensitivity (93.3-98.5%) and specificity (95.3-98.6%) 3. Additionally, altered PSG3 levels in maternal plasma appear associated with twin-twin transfusion syndrome development 4. Recent cancer research suggests PSG3 expression may have sex-specific prognostic significance in female lung adenocarcinoma patients, potentially through KRAS signaling pathway modulation 5. These findings indicate PSG3 functions primarily in pregnancy maintenance while potentially serving broader roles in disease pathogenesis.