Weed doesn't hurt the baby, i know a lot of people who smoke while they were pregnant and their babies are smarter then a person who doesn't smoke weed.. the only thing weed does, is make you hungry.. happy..and tired. It relaxes you. You can't even over dose on weed!!!
Not only is the action of smoking itself is detrimental to the health of the baby, but we do not know how cannabis intake can affect the developing brain. If you were using it for nausea, you may have hyperemesis gravidarum, a condition that causes excessive nausea and vomiting during early stages of pregnancy. There are other medications that are proven safer during pregnancy that are effective for nausea that your OB can prescribe for you. If your OB is aware of your issue they will be happy to address it. However you did not say you are feeling sick and are using it only to increase your appetite. Your appetite will increase in a few weeks even if you do not smoke mj and the baby will not be harmed as long as you do not intentionally starve yourself.
You want to eat right and stay away from all unneeded drugs and alcohol while you are pregnant and nursing or mothering young children. Please take good care of yourself and that way you can be sure you are taking the best care of your child!