Zygote serine decreased uptake from the fertilization medium is associated with implantation and pregnancy

Purpose: To identify an association between amino acids (AAs) metabolism and reproductive outcome. Methods: Prospective collection, observational study, in patients undergoing fresh, double embryo transfer (ET), in a tertiary hospital referral IVF unit. Spent day 1 and day 3 media were collected. Concentrations of taurine, aspartic acid, proline, and serine in the medium were determined using a liquid-chromatography mass-spectrometer (LCMS/MS). Data was analyzed according to excretion versus uptake, and a cut-off value was calculated based on a receiver operating curve (ROC). Pregnancy rates were also calculated after stratification into subgroups in accordance with AA metabolism. Results: Seven out of 19 patients conceived (36.8 %). The ORs for pregnancy when the zygotes secreted aspartic acid, serine and proline above the cut-off value were 2.9, 5.67 and 5.21 (p<0.05). When both transferred embryos were above the cut-off value of serine the PR's were 62.5 %, 12.5 % when both were below, and 33.3 % when one was above and the other below (p=0.04). Similar results were obtained for proline; PR's were 66.7, 18.7 and 28.6 % respectively, but with a borderline statistical significance (p=0.08). The same trend was observed in the case of aspartic acid but not near statistical significance. No differences in PRs were found in association with taurine turnover during fertilization or any of the studied AAs during the cleavage stage. There was no correlation between zygote or embryo AAs metabolism and embryo morphology. Conclusions: Serine and possibly proline decreased uptake from the fertilization medium is associated with pregnancy and might be useful for embryo selection.