Smoking is a health hazard, and it's something you shouldn't be doing especially when you're pregnant. Here are some 4-D ultrasonic scans of two different fetuses to show the difference in mothers who smoke and mothers who don't.

The top row shows a fetus whose mother is a smoker. The bottom shows the fetus of a mother who doesn't smoke.

According to researchers, fetuses whose mothers were smokers showed a significantly higher rate of mouth movements than the normal movements expected in a fetus during pregnancy. This is a close-up of the fetus exposed to cigarette smoke:

It looks like it's grimacing and rubbing at its eyes as if the cigarette smoke is bothering it.

The reason for that, could be fetal central nervous ystem not developing at the same rate in the same manner as in fetuses of mothers who did not smoke.

This one here is a close-up of a non-smoking fetus. Look at how it is taking a nap.

So the key takeaway here is: don't smoke. Regardless of whether you are pregnant or not.