How far back does a meconium drug test on a newborn go?

Last trimester:: Meconium is preferred over urine for testing of neonates. Urine testing indicates drug use only over the last 1–10 days, depending on the drug. Meconium documents drug use over an extended period of time, covering at least the last trimester of pregnancy.

Second trimester: Meconium starts forming in the second trimester, so theoretically substance use in second trimester could cause drug to be detected in the meconium, Though last trimester use is more likely to be picked up.