Dear Catherine: My references are at work, so I will try to describe as best I can what I have come to understand. (If anyone understands this more than me, please explain it to me better!!) I will provide the references when I uncover them (I used to think piles were hemorrhoids, now I know they are large stacks of "to read" articles stashed all around the places I live and work!) Ketones are by-products of fat metabolism (when fat burning takes place as the nearly exclusive energy source--remember the Dr. Adkins Diet in the 1970s?). Ketones are normally taken care of by the body when the rate of production is low. Excess ketone production (which often takes place in diabetes) can lead to acidosis and even death. In late pregnancy, the hormonal picture of the mother is altered so that she is insulin resistant and preferentially burns fat to free up glucose, the preferred fuel for the baby. This is the time of rapid brain development (for the baby, that is, the mother's seems to go into remission...). When ketones are high enough to be spilled into the mother's urine, it is a definite signal to take action (get the mother to eat at more frequent intervals.). The time span between spilling ketones and the last feeding is individual. I find the most obese women need to eat the most frequently (but not soda-pop and chips or desserts). I f diagnosed with gestational diabetes, these large women cannot maintain their high caloric intake (ever try to fit 2800 cal of complex carbohydrate, protein and fat into a pregnant woman?) and, in my clinical experience lose some weight. Most of the information regarding ketones and brain development is directed toward gestationally diabetic mothers. Our clinic tests all pregnant mothers' urine for ketones on routine OB visits, but I'm not sure what they do when they find it besides write it on the chart. (I guess I'd better inquire). Acidosis is not the most favorable environment for brain growth (ketones can and do cross the placenta). Hope this helps a little.... Martha Grodrian Brower, RD, LD, IBCLC Nutrition Trivia de jour