Wow... I really don't know how to comment without sounding mean and or nasty. I am 46 years old and have respiratory problems because my birth mother decided it was okay to smoke through the pregnancy. (That was well before we know what we know now.) What we do know now is that it is not acceptable at all to expose a developing fetus to any level of nicotine and the more than 100 potentially cancer causing agents in smoked tobacco.
This is a serious matter, and I am not trying to sound mean or nasty but you have to know that continuing to smoke is doing harm to your baby. Maybe you don't see it on ultrasounds, but I can guarantee you that damage is being done.
At the very least, try the e-cig thing. You'll still be blasting your child with doses of nicotine that can kill laboratory rats whose immune system has been compromised, but you won't be blasting your child with all of the other toxins and cancer causing agents.
If you do anything for your baby, please quit... My birth mother didn't, and 46 years after my birth I still have respiratory problems tied directly to my mothers smoking. Not paying attention to this warning or any others is just that same as purposely harming your baby, and I don't think you want to do that.
I am 16+2 weeks pregnant, I smoked for 16 years prior to pregnancy. I have been using an e cigarette (FUMA BRAND to be exact) for over 5 weeks. I use it only when im craving nicotine. Even my dr. told me it is better for the baby becaus erthere isn't all the rat poisoning and cyanide and crap in regular cigarettes. I find myself hitting the e-cig less and less as the days go by. My baby is perfectly healthy so far.