Welcome to JA. How long a drug is detectable in your system depends on age, sex, weight, metabolism, and how much and how often you use. Marijuana metabolizes very slowly and is stored in fat. For an infrequent user, it is detectable for up to 10 days. For a chronic user, it can be 6 weeks. Anytime it's in your body, it's also in your baby's body as well.
Since the marijuana metabolites are stored in fat, there really is no proven way to effectively speed them out of your system. Drinking plenty of water and walking 30 minutes a day are good for your metabolism, but it helps only a little.