<prompt> Most impoant factor determining the affect of anaesthetic agent on fetusDuration of pregnancyMACProtein bindingRoute of anaesthetic  <response>: All the given options determined the effect of anaesthetic on fetus. But, duration of pregnancy is the most impoantAlmost all anaesthetic agents can be potentially teratogenicDay 15th to day 60 is the most critical period.Refer: Morgan and Mikhails Clinical Anaesthesiology, 5th edition, pg no. 846 