The first method developed involved weighing the baby before and after a feeding in an attempt to determine how much breast milk the baby was taking. This was cumbersome, not to mention inaccurate since home scales often cannot reliably detect such small changes in weight. Samples of the mother's breast milk were also analyzed for phe content. Based on blood levels, adjustments were made in the amount of time the baby was allowed to breast feed or in the number of breast feedings the baby was allowed each day. Newer methods are much easier for the mother and now many women with a baby with PKU opt to continue breast feedings.
Breast milk is lower in phenylalanine than most regular infant formulas.
This means that the baby can take a greater volume of breast milk than infant formula to meet his or her phenylalanine requirements. The newer formulas for infants with PKU have no phenylalanine. Lofenalac has some phe in it, but Phenex 1 or Analog do not. If the baby uses one of the new formulas, the baby is allowed more breast milk in a day. A method has been developed that allows more freedom in feeding.