Newborns are unmistakably (and adorably) tiny, but babies born too small (under 5.5 pounds) have a greater risk of serious health issues at birth and later in life than babies born at a healthier weight. A number of things can lead to babies being born underweight, but few behaviors pose as great a preventable risk as smoking and drinking while pregnant.

Smoking

Smoking during pregnancy can increase the chances of a long list of dangers — from miscarriage and birth defects to dying from Sudden Infant Death Syndrome (SIDS) during infancy to developing diabetes or breathing problems later in life. The risks from cigarette smoke go beyond just a mom smoking. Simply being around cigarette smoke can increase the likelihood that a pregnant woman will give birth to a low birth weight baby.

According to the Centers for Disease Control and Prevention (CDC), no amount of exposure to cigarette smoke is considered safe for pregnant women or children, which is why avoiding smoke as much as possible during pregnancy is an important part of keeping you and your baby safe.

A primary concern regarding tobacco use or exposure while pregnant is the risk that the baby will be born too early and/or too small. While it’s not clear exactly how tobacco leads to low birth weight, nicotine and other chemicals in cigarettes can cause blood vessels to narrow, restricting the blood flow to the baby and limiting the amount of oxygen and nutrients they get during pregnancy. This, in turn, can potentially keep the baby from growing properly and prevent them from reaching a healthier weight.

An estimated 12.4 percent of babies born to smokers are underweight, compared to just 7.7 percent of babies born to nonsmokers. According to an estimate by researchers at Florida State University, if all Florida moms were to avoid smoking and receive prenatal care during pregnancy, the number of low birth weight births could drop by nearly 8 percent, and infant deaths could be reduced by 12.5 percent.

Alcohol

Alcohol use during pregnancy, like tobacco, has been linked to a wide range of health concerns, including both physical and intellectual issues like low birth weight. When pregnant women drink alcohol, their unborn babies drink it, too. A large amount of the alcohol consumed crosses the placenta and gets into the baby’s body, increasing the risk of health concerns by affecting hormones and disrupting the baby’s development.

Similar to nicotine, alcohol can restrict blood flow to the placenta, which, in turn, can impact how much oxygen and nutrients a baby gets in the womb. In addition to limiting how big the baby can grow, alcohol use in pregnancy can lead to other issues, too, namely birth defects, intellectual disabilities, and behavioral challenges later in life. Because of these risks, the CDC cautions that no amount of alcohol has been shown to be safe during pregnancy, and women should avoid it completely if they think they could get pregnant.