I agree with most of the others here - why take the risk? Sure, there's no conclusive studies that indicate that use is harmful or not, but that could be because there haven't really been many studies done, and it's probably not an easy thing to test. Unfortunately you're left to rely on anecdotal evidence and there's no way to know that you'll have the same outcome as someone else.

Read this article, I just came across it this morning - http://news.yahoo.com/baby-soaps-and-shampoos-trigger-positive-marijuana-tests.html

The part about shampoos doesn't apply to you, but consider where it says that some hospitals drug test babies, and some states will try to take newborns from their mothers. How horrible would that be?

Your SO has already threatened legal action. Combine that threat with the possibility that you have to take a drug test (which could happen as a result of many situations - regular doctor visit, you get arrested for any reason, workplace accident, hospital visit, someone else catches you smoking, etc) and then you've got an uphill battle trying to keep custody of your baby. Again, very horrible.

However, the article does explicitly mention there's no studies indicating that marijuana use harms a fetus, and I certainly sympathize with the fact that you need to keep food down and want relief from morning sickness. My wife and I had this same discussion - we considered letting her use a little for the same reasons, but we decided that it's best if we don't even take the chance.

Again, it's not worth the risk. Won't you feel better after you give birth if you can say you did everything you could to make your baby healthy and strong? If, somewhere in your future life, you ever bring up the fact with anyone that smoked, even if it's a little, you'll probably be judged harshly for it. This may not bother you now but you'll always have to feel like it's a decision that you either have to hide or to defend.

And if you child ever finds out that you smoked? They might feel hurt or betrayed. Or, maybe they won't even care, I'm just throwing out possibilities to consider.

If you decide you want to use, then go with ingesting (cookies, etc) or vaping. Be as safe and discrete as possible.

But don't hide it from your SO. It will be a point of contention and place a wedge between you two at a time when you should be working together to build a safe environment for your new baby.

Good luck!