Coach Smith jumping in here. Last year I dug through at least 15 source books - pediatric texts, maternity/nursing texts, LC texts, WHO and UNICEF guidelines, etc to find criteria for supplementing, deciding whether the baby was OK, etc. The 10% weight loss figure is far from universally accepted, and as far as I could tell is NOT well documented. Most sources I examined would tolerate a baby's 5-10% weight loss before becoming excited. No source was worried if the weight loss was under 5%; no source advised only watchful waiting if over 15%. However, the sources also listed other criteria for deciding whether a baby was "doing well." These criteria included poops, pees, general behavior, color, how the baby "looked", whether he fed well or not, etc. The professional was expected to use several criteria for making a decision whether or not to intervene with what the mother was trying/doing. Sure, weigh the baby. Why not? Weight is one indicator of what's going on. Just don't stop there! Watch the baby feed - and I mean the ENTIRE feeding - for quality and quantity and rhythm etc of the process. Take a thorough history. LOOK at the entire baby - including making eye contact with him/her. Babies eyes tell enormously important stories. Do other tests, observations, etc as the situation calls for. THIS is professional behavior - to carefully gather lots of data, weigh all the factors (no pun intended), consider the social and emotional context, and offer options to the mother. First, do no harm. Make sure that anything you suggest is not going to make the situation worse for the baby, who is the most vulnerable member of the breastfeeding team. Or for the mother, who will be responsible for this baby for the next 20 minutes, 20 weeks, 20 years and whose body is the baby's source of food and immune function for the next half year at least. Their relationship is fragile too, and carelessly interfering with it can have serious consequences. It's a balancing act. We walk a fine line in helping many of our mother-baby clients. Too little intervention, and we may put someone in jeopardy. Too much intervention, and we may put someone in jeopardy. This is why we need to work together, keep reading and studying, and never allow ourselves to become arrogant about how much we know. Just when we think we know something about breastfeeding..... the next mom or baby will challenge our complacency once again. And someone ELSE will have a piece to the puzzle that we don't have. Happy holidays to all! Linda J. Smith, BSE, FACCE, IBCLC Bright Future Lactation Resource Centre Dayton, OH USA http://www.bflrc.com