The Use of the Prognostic Nutritional Index in the Selection of High-Quality Embryos for In Vitro Fertilization: A Prospective Analysis of Unexplained Infertility in Non-Obese Patients

Background: Unexplained infertility (UI) affects a significant portion of couples worldwide, posing challenges for effective treatment. The prognostic nutritional index (PNI), traditionally used in oncology, has been adapted to evaluate reproductive outcomes, particularly in the context of in vitro fertilization (IVF). Method: This study analyzed 198 non-obese couples undergoing IVF for UI at a tertiary care center between February 2023 and December 2024. This study assessed the correlation between the PNI, comprehensive hematological profiles, and IVF outcomes, including embryo quality and pregnancy. The PNI was obtained through serum albumin and lymphocyte counts. Results: The PNI was elevated in the high-quality embryos (51.65 ± 5.09) compared to those of mild-quality (48.10 ± 2.82) and low-quality (44.20 ± 4.16) (p = 0.0001). A higher PNI was associated with improved embryo quality, with an odds ratio of 11.859 (p = 0.0001) for higher quality embryos. Other inflammatory markers did not demonstrate a predictive value for IVF outcomes (p > 0.05). The PNI yielded an area under the curve (AUC) value of 0.895 (95% confidence interval (CI): 0.85–0.94; p = 0.001), indicating robust discrimination. At a cutoff of 46.5, the PNI demonstrated 81.2% sensitivity and 80.1% specificity, further underscoring the potential of this index as a discriminative marker. Conclusions: The PNI serves as a strong indicator of IVF outcomes, correlating directly with embryo quality and the success of fertility treatments. Moreover, the predictive potential of the PNI for embryo quality in reproductive medicine highlights the intersection of nutritional and immunological status with reproductive health, offering a framework for enhancing clinical assessments in IVF.