Purpose To determine the association between ammonium concentration in culture medium and blastocyst development and to assess the influence of increased ammonium concentration on the expression of Bax, Bcl-2 and Oct4. Methods A total of 254 cleavage-stage embryos were individually cultured in 30 mu L G2-plus medium on Day 3, and then culture media samples were collected on Day 5 for ammonium concentration determination immediately after evaluating the embryos morphology. Poor-quality blastocysts (combined score of CC) were used for gene expression analysis. The blastocyst formation rate, good-quality blastocyst rate and relative expression levels of Bax, Bcl-2 and Oct4 were analyzed. Results Based on receiver operating characteristic curve, the cutoff value of ammonium concentration produced by embryos was 16.07 mu mol/L (AUC = 0.722, 95% CI 0.637-0.807; P = 0.000), so all embryos were assigned to two groups according to the cutoff value: normal group (< 16.07 mu mol/L) and increased group (>= 16.07 mu mol/L). There was a significant difference in blastocyst formation rate (80.5% vs 59.0%, P < 0.01) between normal group and increased group, as well as for good-quality blastocyst rate (21.0% vs 3.4%, P < 0.01). A significantly higher expression level of Bax (P < 0.05) and considerably lower expression level of Oct4 (P < 0.01) were observed in increased group compared to normal group. Conclusion Our data demonstrated for the first time that increased ammonium concentration in culture medium may promote cellular apoptosis and negatively affect pluripotency of human blastocyst.
