Here's another reason why you should refrain from smoking during pregnancy: Smoking During Pregnancy Increases Risk of Pre-Eclampsia.

The study of 1001 women found that smokers in the group are more likely to deliver prematurely (before 34 weeks), produce lower birth weight babies, or have babies with adverse outcomes than women who don't smoke. Smokers were also five times more likely to develop eclampsia.

What is pre-eclampsia?

Affecting at least 5-8% of all pregnancies, it is a rapidly progressive condition characterized by high blood pressure and the presence of protein in the urine. Swelling, sudden weight gain, headaches and changes in vision are important symptoms; however, some women with rapidly advancing disease report few symptoms.

How serious is it? It's the second most frequent cause of death in pregnancy in the US.