P-241 The in vivo human uterine pH and uterine fluid composition differs from pH and composition of clinically used in vitro preimplantation embryo culture media

Abstract Study question To study the pH and uterine fluid composition in the human uterus three days after a positive LH test or ovum pick-up. Summary answer The uterine pH three days after a positive LH test or ovum pick-up was 6.8. Concentrations of 37 components were determined in uterine fluid. What is known already In assisted reproductive technologies (ART), the in vitro culture of human preimplantation embryos is known to play a crucial role in the success of In Vitro Fertilization (IVF) treatments. It affects live birth rates and child outcomes such as birth weight. Numerous commercial embryo culture media are routinely used in clinical practice worldwide, but their composition is primarily based on laboratory-based clinical insights and experimental studies with animal models. Studies on the natural human preimplantation embryo environment during the physiologically relevant time of the menstrual cycle are limited. Study design, size, duration A cross sectional clinical study was conducted to study the uterine pH and the composition of human uterine fluid. The uterine pH was measured in 53 women on the third day after LH surge (N = 46) or ovum pickup (N = 7), as that time in the menstrual cycle is associated with endometrial receptivity for embryo implantation. Twenty-two samples of aspirated uterine fluid, that were collected at the same time, were analyzed for the concentrations of thirty-seven components. Participants/materials, setting, methods Healthy women of reproductive age with normal functional uterine anatomy were included. Uterine pH was determined using pH probe inserted through outer sheath of an Embryo Transfer (ET) catheter at the lithotomy position. Uterine fluid was then aspirated using a syringe connected to outer sheath of this ET catheter. Collected samples were analyzed using a Cobas 8000 chemistry analyser and ultra-performance liquid chromatography-tandem mass spectrometry. Main results and the role of chance The mean pH in the uterine cavity on the third day after a positive LH test (6.75 ± 0.22) or ovum pick-up (6.82 ± 0.18) was clearly lower than the pH used in routine clinical practice for preimplantation embryo culture (pH 7.3 ± 0.1). Calcium, phosphate, lactate(L), pyruvate, albumin and 21 amino acids were present at different concentrations in human uterine fluid compared to most commonly used preimplantation embryo culture media. Immunoglobulins, citrulline, ornithine and uric acid were present in uterine fluid, but not in clinically used culture media. Limitations, reasons for caution As the uterine cavity is only one part of the reproductive tract, our measurements do not fully represent the complete in vivo environment of preimplantation embryo development. We only studied 37 components, recognizing that uterine fluid likely contains additional components. Wider implications of the findings The observed differences between the uterine pH and the composition of uterine fluid and the pH and composition of preimplantation embryo culture media used in routine clinical practice could be a starting point to further optimize in vitro embryo culture in ART treatments. Trial registration number Not applicable