Fetal abnormalities produced after preimplantation exposure of mouse embryos to ammonium chloride

BACKGROUND: The aims of this study were to determine whether preimplantation exposure of mouse embryos to ammonium resulted in abnormal fetal development and to evaluate similar risks to the outcome of human assisted conception. METHODS: Mouse embryos cultured from the 1-cell stage were exposed to 0.3 mmol/l ammonium chloride for 3 days. Embryos cultured from the 2-cell stage were exposed to 0.3 or 0.6 mmol/l ammonium for 2 days. After transfer to the uteri of pseudopregnant recipient females, post-implantation development was evaluated on embryonic day 15.5 (E15.5) or E18.5. RESULTS: There was no consistent effect of preimplantation exposure to ammonium chloride on fetal or placental weights. All 101 E18.5 fetuses were normal but 5/217 E15.5 fetuses were abnormal (three exencephalic and two polydactylous), which was signi®cantly higher than the 0/363 for the pooled groups of E15.5 control fetuses (P = 0.007). The combined E15.5 and E18.5 frequency was also signi®cantly higher than the controls (5/318 versus 0/433; P = 0.013). CONCLUSIONS: These results support the conclusion that abnormal preimplantation culture conditions can cause fetal abnormalities in mice, but the risks may be lower than previously suggested. Further work is needed to evaluate the risk more fully but this risk should be considered when designing new strategies for human assisted conception. Key words: ammonium/culture/fetal abnormality/preimplantation embryo/preimplantation teratolog