Abstract
PURPOSE: To evaluate whether reduced oxygen tension (5% O(2)) during embryo culture is associated with differences in neonatal outcomes compared with atmospheric oxygen (20% O(2)) in fresh IVF/ICSI singleton births. METHODS: We conducted a retrospective cohort study at Peking University Third Hospital (2015-2022), including 13,831 singleton live births after fresh cleavage-stage transfers. Neonates conceived under 5% O(2) (n = 3192) were compared with 20% O(2) (n = 10,639). Primary outcomes were gestational age, birthweight, and gestational age and sex-adjusted Z-scores; secondary outcomes included small-for-gestational-age (SGA), large-for-gestational-age (LGA), and macrosomia. Multivariable regression adjusted for maternal/paternal age, body mass index (BMI), infertility type, stimulation protocol, gonadotropin dose, fertilization method, endometrial thickness, number of embryos transferred, and culture medium. Birthweight-related outcomes were further adjusted for gestational age and sex. RESULTS: Compared with 20% O(2), 5% O(2) was associated with longer gestation (β = 0.073 weeks; P = 0.009), lower birthweight (β = - 44.6 g; P < 0.001), and lower Z-scores (β = - 0.105; P < 0.001). SGA risk increased (OR = 1.26; P = 0.030), while LGA (OR = 0.80; P < 0.001) and macrosomia (OR = 0.81; P = 0.006) decreased; preterm birth did not differ. CONCLUSIONS: Reduced oxygen tension during embryo culture was associated with lower neonatal birthweight and a reduced incidence of LGA or macrosomic infants, indicating a favorable effect on neonatal outcomes. Prospective multicenter and mechanistic studies are warranted to confirm these findings and refine oxygen management in Assisted reproductive technologies (ART).