Background: There is still uncertainty regarding the association between maternal serum levels of retinol-binding protein 4 (RBP4) and pregnancy outcomes. This study aimed to determine the association between RBP4 levels and incidence of small/large for gestational age (SGA/LGA) infants among the Chinese population.

Methods: This was a retrospective study of 11,854 pregnant women who delivered at Changzhou Maternal and Child Health Care Hospital between 2016 and 2017 and whose serum RBP4 levels were measured at the time of admission. The incidence of SGA/LGA deliveries was retrieved from the medical records of the participants.

Results: Maternal RBP4 levels in the second, third, and fourth quartiles (28.8–34.0, 34.1–40.0, and >40.0 mg/L, respectively) were associated with lower birthweights relative to those in the first quartile (<28.8 mg/L), with estimated average decreases of 51.30 g (95% confidence interval [CI], −70.51 to −32.10), 86.86 g (95% CI, −106.50 to −67.22) and 124.08 g (95% CI, −144.51 to −103.64), respectively (P for trend <0.01). Pregnant women in the fourth quartile for RBP4 levels had a greater SGA risk (odds ratio [OR] 2.14; 95% CI, 1.72–2.65) and lower LGA risk (OR 0.53; 95% CI, 0.45–0.63) than those in the first quartile after controlling for demographic variables, gestational age, pregnancy complications, and other laboratory results. The sensitivity analysis indicated the consistency of these findings.

Conclusion: High RBP4 levels in late pregnancy are associated with an increased SGA risk and decreased LGA risk, indicating that serum RBP4 levels at the time of admission for delivery could be a promising predictor of SGA/LGA delivery.