Evaluating the effects of smoking during the first trimester of pregnancy

This study looked at the pregnancy outcomes of women who smoked only during their first trimester. This study found that women who quit smoking early in pregnancy had a lower risk of having a baby with a low birth weight.

Tobacco smoke contains numerous chemicals that may be harmful during pregnancy, including nicotine and carbon monoxide. Babies of women who smoke during pregnancy are more likely to have a low birth weight. Some studies suggest that babies of women who quit smoking during pregnancy have similar birth weights to those of non-smoking women.

The health of newborns’ bodies can be measured in several ways. Doctors can measure their weight, length, the circumference of their heads, and other body proportions. The effects of smoking during the first trimester on the body proportions of newborns are unclear.

This study included 1.38 million women who gave birth to single babies (not twins). 84.5% of women did not smoke. 3.5% quit during the first trimester, and 12% continued smoking after the first trimester.

Women who continued smoking throughout pregnancy had a significantly higher odds of having a baby with a low weight compared to women who quit smoking during the first trimester (2.22-fold vs. 1.10-fold). Women who continued smoking were also more likely to have a baby with a small body length (2.26-fold vs. 1.16-fold).

Smoking increased the risk of having a baby with unusual body shape, such a large head compared to the rest of the body. This risk was greater for patients who continued smoking compared to women who quit (22% vs. 9%). The risk of having a baby with a small brain compared to body size was similar between the two groups (11% vs. 8%).

This study found that quitting smoking during the first trimester greatly reduced the risk of having a baby with a low birth weight. However, their babies were still more likely to have unusual body proportions such as a short body length.

This study was not able to consider the effects of secondhand smoke, such as from other household members.

If you are pregnant or planning a pregnancy, talk to your doctor about quitting smoking.