Humidified culture in a dry incubator improves culture performance

Objective: This study aimed to determine whether localized humidification within a dry incubator could mitigate increased osmotic pressure in the culture medium and improve embryo development and clinical outcomes.Methods: In vitro culture and pregnancy outcomes were retrospectively compared between a dry incubator group (K-dry) and a conventional humidified incubator group (WJ). In addition, a K-humidified group was prospectively established by adding 4 mL of human tubal fluid medium outside the wells in a dry incubator to assess whether localized humidification improved outcomes compared with conventional dry conditions.Results: In the two-group comparison, the WJ group had significantly higher rates of good-morphology day 3 embryos, blastocyst formation, and good-morphology blastocysts than the K-dry group (p<0.05). In multivariate analysis, dry culture conditions were independently associated with poorer developmental outcomes. In the three-group comparison, the K-humidified group had a significantly higher rate of good-morphology day 3 embryos than the K-dry group (p=0.011) and did not differ significantly from the WJ group. Clinical pregnancy and ongoing pregnancy rates did not differ significantly across the study groups.Conclusion: Dry culture conditions may compromise embryo quality through osmotic stress. Localized humidification within a dry incubator was associated with improved early embryo development and increased the number of embryos suitable for transfer or cryopreservation, with comparable performance to a conventional humidified incubator. However, once embryos reached a transferable blastocyst stage, implantation potential appeared to be driven primarily by intrinsic embryo competence rather than by the prior culture environment.