How can i prevent my baby to become constipated? she is 4 weeks old and on nan pelargon formula

Not necessary: If your baby is feeding well and having a soft stool at least daily or even every other day, this is normal and I would not recommend making any changes. Breastfed babies will tend to go more frequently and breast milk will provide the best nutrition. If the stools become hard or less frequent, there are some formulas (Enfamil Regulin) that are designed to promote more frequent stools.

Constipation: Increase her water intake. Good Luck