First off, I don't know how this has been proven---I only go by what I've witnessed in my 75 years. Smoking was never an issue for pregnant women or any one else, back in the day (don't remember when this warning began).
No one told women they could not/should not smoke while pregnant yet they did not have unhealthy babies .Sure, some babies were and are born with serious problems---whether their mothers or fathers smoked or didn't. You must know some cases. We do not know all the answers to why this happens---heredity, recessive genes, parents' ages, etc.
No, you are wrong to conclude that I promote smoking. What I object to is unproven information.
This is a major reason the smoking wars are over, and smokers lost. Bigtime. It isn’t a conservative value to put the health of your fetus at risk. To play Russian Roulette with an unborn babies health.