Normal variation in breastfed infant bowel movements: Breastfed infants often have a different bowel movement pattern compared to formula-fed infants. They may have a stool after every feeding or may go several days without a stool. This variation is due to the efficient absorption of breast milk, leaving little residue to form stool.

Dehydration: Although less common in breastfed infants, dehydration can occur if the infant is not latching properly or if the mother's milk supply is low. Dehydration can cause a decrease in stool output.
Underfeeding: If the breastfed infant is not getting enough milk, it can lead to decreased stool output.
Foremilk imbalance: An imbalance between foremilk (the milk that comes at the beginning of a feeding) and hindmilk (the milk that comes at the end of a feeding) can cause digestive issues, including changes in stool patterns.

Hirschsprung's disease: A congenital condition characterized by the absence of ganglion cells in the distal bowel, leading to severe constipation or intestinal obstruction. It's crucial to diagnose this condition early to prevent complications.
Intestinal obstruction: Any condition that causes a blockage in the intestines can lead to a lack of stool passage. This is a medical emergency.
Cystic fibrosis: Although less common, cystic fibrosis can cause gastrointestinal symptoms, including constipation or intestinal obstruction due to thick, sticky stool.

Hypothyroidism: Congenital hypothyroidism can cause constipation among other symptoms.
Spinal cord anomalies: Certain spinal cord anomalies can affect the nerves that control bowel movements, leading to constipation or lack of stool passage.
Gastrointestinal anomalies: Conditions like intestinal atresia or stenosis can cause an obstruction that leads to a lack of stool passage.