Estimated effects and 95% confidence intervals to the left and right of the inflection point were -55.20 (-75.57 to -34.82) and 77.33 (22.48 to 132.19), respectively.<h4>Conclusions</h4>A U-shaped relationship between serum ApoA1 and SUA was identified in OPF patients. This evidence concerns the gene APOA1 and Single umbilical artery.