This is a tricky question. You should
definitely not use it below three months of age as babies below three months old are too stimulated with the picking up and putting down and they burn far too many calories in the process. Between 3-4 months is a bit of a gray area. For many babies, pu/pd may still be too stimulating and, therefore, unsuccessful.
For babies younger than four months, the primary babywhisperer tool for sleep training should be the
“Four S” wind down and the
shush-pat method. To wean a pacifier in a young infant, consider trying the
Gradual Weaning Process; to wean feeding-to-sleep in a young infant, consider trying the
Gentle Removal Plan.
Generally, you can use a
version of pu/pd with a baby of four months or over; however, even some four month olds are not ready for it so you should always try shush-pat in the first instance. It’s best to wait as long as you can; generally by 5-6 months most babies are ready for PU/PD. Again, it’s best used if all other methods have been tried and have failed.
**For more detailed information about why pu/pd shouldn’t be used with young infants, see, The Babywhisperer Solves All Your Problems by Tracy Hogg and Melinda Blau, Chapter 5: Teaching Babies How to Sleep, the section entitled, "Improper Intervention: No P.U./P.D. Before Three Months" (near the end of the chapter).
