Not really. This definately deserves a close consultation with your doctors. The only safe recommendation is to quit both. Depending on the level of substance dependence/abuse a physician might be comfortable replacing the illicits with pharma. By that i mean Marinol instead of thc. Amphetamines cause fetal hypertension, possible strokes, slowed growth, poor nutrition, and birth defects.
Don't conceive. Don't get pregnant until you get off drugs, meth in particular. If you do, chances are the state will take your child.
Possible. It is possible to use Methadone to quit methamphetamines during pregnancy (no drug to get off of cannabis), but this is not recommended. Absolute best thing to do is get off the drugs completely before getting pregnant. As the saying goes, if you're not ready to get off drugs before pregnancy, you won't be ready to get off the drugs during pregnancy.