In the United States, fetuses at risk for drug exposure (and having a teenage mother is considered a risk factor) are frequently tested at birth for drug exposure. THC is one of those drugs that are screened. Every state has different laws about how these situations are treated, but a positive drug screen in an infant usually mandates a social work referral. In an adult, THC can come up positive on a blood test (which is how they test for drugs in the hospital) up to 45 days from exposure. There is not a lot of medical information about how long the drug remains in the fetus, because it is difficult to study pregnant women who use marijuana because of legal issues, but since the drug crosses the placenta, I think it is safe to assume that the fetus can also test positive 45 days after exposure. I hope this information was helpful, and because the safety of marijuana has not been able to be evaluated fully in pregnancy, that your try alternate methods to control your nausea. Good luck with your pregnancy.