Is tobacco use a risk factor for low birth weight or premature birth? Are there other modifiable risk factors ?

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Yes. Tobacco use is the most important modifiable risk factor associated to prematurity and low birth weight. It is established that maternal tobacco use as well as maternal exposure to second-hand smoke both cause a reduced birth weight. Using other substances such as alcohol and drugs is also associated with prematurity and low birth weight.

To learn more about the consequences of prematurity and low birth weight, click here.

Other maternal behaviors can put the baby at risk of low birth weight and prematurity.  The following table groups these behaviors.

Tobacco use X X
Alcoholism X X
Drugs (cocaine, narcotics,  amphetamines, heroin) X X
Second-hand smoke X


Nicotine and carbon monoxide reduce the blood flow and the concentration of oxygen for the fetus due to physiological changes of the placenta. Furthermore, carbon monoxide reduces the availability of hemoglobin (a transport molecule in the blood) to be able to transport oxygen to the fetus. In addition to prematurity and low birth weight risks, tobacco use can have an effect on the infant’s development, causing a multitude of congenital malformations. We evaluate that an annual reduction of only 1% of tobacco use in the United-States would save 21 million dollars in health care, solely for newborns. In Canada, in 2005, 13.4% and 14.2% of women respectively declared to have smoked or have been exposed to second-hand smoke during their pregnancy. Tobacco use not only affects the infant, but also the mother, increasing her risk of lung cancer and infertility. For these multiple reasons, total abstinence from tobacco is recommended during pregnancy. It is even recommended to avoid second-hand smoke that can come from family members.


It is proven that alcohol consumption reduces cellular division (fetal growth). There is no minimal alcohol quantity that is judged to be safe during pregnancy. Many studies demonstrated that babies born from mothers that had two drinks per day were of 200g smaller weight at birth. In Canada, in 2005, 10.5% of mothers declared having drunk alcohol during pregnancy, where younger mothers were more likely to engage in this harmful behavior. Alcohol consumption during pregnancy also has an impact on the cognitive development and the intelligence of the infant, even later in life. Due to the important implications of alcohol consumption during pregnancy, total abstinence is recommended during pregnancy.


Cocaine, marijuana, narcotics, amphetamines and heroin are linked to low birth weight and prematurity. To this day, the exact mechanism for each drug is not well understood, however, many will stimulate uterine contractions or affect placental functioning by changing the blood flow that transports the nutrients to the baby. As uterine contractions decrease blood flow from the mother to the fetus, this diminishes the quantity of oxygen and other nutrients that the baby receives. Drug use is also linked to congenital malformations, which can affect the cognitive development of the growing infant. The risks of preeclampsia, post-partum hemorrhaging, miscarriage, or death at birth are also present with drug use. In the case of drug use, it is important that the mother be referred to adequate services to help decrease or cease their consumption during pregnancy.

To learn about strategies to decrease risky behaviors, consult the following articles.

Medical factors can also increase the risk of low birth weight and prematurity in newborns. To learn more, click here.

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Chang, G. (2016). Alcohol intake during pregnancy. UpToDate.

Chang, G. (2016). Overview of substance misuse in pregnant women. UpToDate.

Crane, J. M., Keough, M., Murphy, P., Burrage, L., & Hutchens, D. (2011). Effects of environmental tobacco smoke on perinatal outcomes: a retrospective cohort study. Bjog : An International Journal of Obstetrics and Gyneacology, 118(7), 865-871. doi: 10.1111/j.1471-0528.2011.02941.x

Institut canadien d’information sur la santé. (2009). Nés trop vite et trop petits : Étude sur les bébés de faible poids au Canada.

Institute of health economics. (2008). Alberta, Canada. Determinants and prevention of low birth weight: a synopsis of the evidence. Alberta : Institute of health economics.

Rodriguez-Thompson, D. (2016). Cigarette smoking: Impact on pregnancy and the neonate. UpToDate.



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