Hello dear Understand your concern Yes smoking marijuana is injurious during pregnancy. It contain active ingredient tetrahydrocannbinol. When you smoke it, produce carbon monoxide that decrease the oxygen and so less oxygen reach to the fetus and affect the growth of fetus. It cause high chance of miscarriage, low birth weight, still birth or premature birth of the baby. No any information available on how long it remain in your body and fetus system. But blood test for it may remain positive up to 45-50 days after exposure. So it is clear that it will remain in the body system for at least 45-50 days. I advice you to consult the gynecologist and keep follow up to check growth and development of fetus by USG scan. Hope this may help you Best regards Dr. Sagar