I agree with Adgal. I think you are in denial about your problem. You are NOT a recreational user if you are using when the consequences of doing so are so serious.
Think about it this way...the reason they are concerned about your use of marijuana is because of what it can do to your baby. If you aren't an addict and CHOSE to use recreationally while pregnant, endangering your baby on purpose...what does that say about the kind of mother you are? At least with an addict one can somewhat understand that your decision making in this area is compromised...
I am very glad that you chose to disclose your drug use and feel that is a step in the right direction. I also feel you need help if you are going to be a good mother to this baby...and you owe it to your baby to do what is in his or her best interest...
The meconium is sent and will show a drug was used at some point. They also test urine to see if it has been recently.
It takes at least 30 days for marijuana to clear out of ones system. Seeing as you are due In About 3 weeks I don't see how it would not show up on the drug screening. Unless it was more then a week and a half ago that you used.
I'm honestly not certain if it will show in your babies feces or not at that point. However, I work in social services, and there are a few things I do know.
They typically prefer not to remove children from their mothers. Most agencies will work hard with mom in an attempt to keep the family intact and get mom whatever help and resources she needs. I'm going to be honest with you (as I see this regularly). Honey, I am not being judgemental or mean. I haven't walked in your shoes, nor do I know anything about you or your life. But based on the choices you made knowing the possible consequence was losing your child, do you not think that is possibly a sign of maybe having a problem with this drug? Again, not being judgemental, but am encouraging you to seek help and support. You and your child deserve it, and resources are available to you should you decide you would like to utilize them. I wish you well, I truly do.