It could be a sign of a number of medical conditions (including stroke or bowel obstruction, or it could even be from acid reflux or something simple like a breastfeeding mother's nipples bleeding and the baby consuming the blood and it showing up. ), or it may be nothing. Watch the baby closely tonight for any unusual signs such as lethargy, lack of appetite, fever, etc. and if any of them develop take her to the ER immediately. If they do not, your decision to take her to the pediatrician in the morning is good. Let them know that there was blood in her stool and you would like to be seen immediately, they should let you have an early appointment. This same thing happened to me when my daughter was 2 weeks old and I was also very very worried and took her to the ped first thing, but everything was OK. However, any time there is blood in the stool of an infant it needs to be treated with the utmost urgency. You are doing a great job.
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