How long do babys go thru withdrawal?

Our daughters bmom used meth the entire pregnancy and even was living in a meth house (where they manufacture the drug) Upon checking into the hospital in labor bmom tested positive but E. once she was born was tested and she tested negative but they kept her for 48 hours observation and she seemed to have none of the withdrawal symptoms. The dr. said it was possible that mom used on and off and had only used to bring on her labor which is why E tested negative. Meth only takes approx 72 hours to metabolise out of the bloodstream of an adult. Unfortunately I have a brother who is heavily addicted to Meth so I have some first hand experience. If he knows he is going to be tested (parole officer etc) as long as he stops using 4-5 days prior he tests clean every time. Its a horrible life ruining drug... anyways... E. is gonna be a year old next month and she is an absolute delight and so far has had no long term affects from the drug use. But as you can see from others stories on here, it seems to be pretty random in that some have babies who have withdrawal problems while others seem not to... Im not sure why, but with the meth exposure in particular there seems to be a lot of gray area as far as the known effects. good luck gina.