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The molarity of the final solution

Developmental or Reproductive Toxicity/ 1-cell (C57BLxCBA/Ca)F2 mouse embryos were cultured in M16, mMTF or KSOM media containing 0 or 0.3mM ammonium chloride for 3 days and 2-cell embryos were cultured in M16 or KSOM media containing 0, 0.3mM or 0.6mM ammonium chloride for 2 days. After transfer to recipient females, postimplantation development was evaluated on embryonic day 15.5 (E15.5) or E18.5. In vivo control fetuses were examined at E15.5 to determine the background frequency of exencephaly … There was no consistent effect of preimplantation exposure to ammonium chloride on fetal weight or crown-rump lengths. All 195 in vivo control fetuses and all fetuses resulting from control cultures (168 examined at E15.5 and 70 at E18.5) were normal. After preimplantation exposure to ammonium chloride, all 101 fetuses examined at E18.5 were also normal but 5/217 E15.5 fetuses were abnormal (3 with exencephaly and 2 with polydactyly). Although 5/217 was much lower than was found in the previous study it was significantly higher than 0/363 for the pooled groups of E15.5 control fetuses (P=0.007). The combined E15.5 and E18.5 frequency was also significantly higher than the controls (5/318 versus 0/433, P=0.013). The results indicate that abnormal preimplantation culture conditions can cause fetal abnormalities but the risk may be lower than previously suggested … This risk … should not be ignored when designing new strategies for human assisted conception