Essential trace element profile in follicular fluid and recurrent pregnancy loss: The role of amino acids—A case-control study

Recurrent pregnancy loss (RPL), defined as two or more consecutive pregnancy losses, imposes a significant burden on both individuals and healthcare systems. Imbalances in essential trace elements (ETEs) and dysregulated amino acid metabolism may contribute to RPL pathogenesis. However, the interplay between ETEs and amino acid metabolites in RPL remains largely unexplored. To address this gap, a case–control study including 69 women with a history of ≥ 2 unexplained RPL as cases and 148 healthy women as controls was performed. The levels of ETEs in follicular fluid (FF) were assessed using ICP-MS, and amino acids profiling was performed using an UHPLC system coupled with a Q-TOF mass spectrometer. Binary logistic regression was used to evaluate the association between each individual element with unexplained RPL risk, while qgcomp and BKMR models were used to assess the joint association between ETE mixtures and RPL risk. Mediation analysis was then performed to investigate the contribution of metabolites to the association between ETEs and unexplained RPL. The study finds that iron levels were positively related to RPL risk (medium vs. lowest tertile: adjusted OR (aOR) = 2.59, 95 % CI = 1.05, 6.39; highest vs. lowest tertile: aOR = 3.31, 95 % CI = 1.37, 8.03). Conversely, cobalt showed an opposite trend (highest vs. lowest tertile: aOR = 0.37, 95 % CI = 0.16, 0.86). In the mixture analysis, iron and cobalt emerged as the main drivers of RPL risk. Furthermore, mediation analysis revealed that L-alanine accounted for the most significant proportion (53.88 %) of the association between iron exposure and unexplained RPL risk. In conclusion, this study revealed that elevated iron levels are associated with altered amino acid metabolism and contribute to the risk of RPL, whereas cobalt exhibits an opposite association. Further research is required to elucidate this interplay.