Quitting smoking before pregnancy reduces risk of low birth weight

If you’re planning to have a baby, quitting smoking sooner rather than later will lower your chance of having a “low birth weight” baby. And the longer you smoke during pregnancy, the greater your baby’s risk. That’s the conclusion of a large study looking at the timing of smoking cessation and the risk of low birth weight or LBW (weighing less than 2.5kg).  

Low birth weight babies have a higher risk of dying as a baby and of many health problems throughout their lives. It’s known that these risks decrease if mothers stop smoking during pregnancy. But until now it’s been unclear exactly when a woman needs to quit smoking to avoid her baby having LBW.

This new study shows how the risk of LBW varies depending on when the woman stops smoking. The researchers looked at the birth weight of almost 200,000 babies who were born full term. They then compared the risk of LBW for babies born to women who never smoked, smokers who stopped before they conceived, smokers who stopped in the first or second trimesters of pregnancy, and women who continued smoking throughout the pregnancy.

They found that babies born to women who stopped smoking before they became pregnant had a similar risk of LBW as babies born to non-smokers. They also showed that compared to babies born to non-smokers, babies born to women who quit in the first trimester had a 26% increased risk of LBW. Babies born to women who stopped smoking in the second trimester had a 100% increased risk of LBW. For babies whose mother smoked throughout pregnancy, the risk of LBW was 146% higher than for babies with non-smoking mothers.

So, the good news to take from this research is that the risk of LBW caused by smoking can be eliminated if women stop smoking before they get pregnant. The sooner you quit, the better!

Source:   Xaverius PK, O'Reilly Z, Li A, Flick LH, Arnold LD. Smoking Cessation and Pregnancy: Timing of Cessation Reduces or Eliminates the Effect on Low Birth Weight. Maternal and Child Health J 2019.