Numerous factors can contribute to a miscarriage. In many instances, doctors do not identify a single cause. However, research suggests that smoking during pregnancy does raise the risk of a miscarriage.

Smoking is just one risk factor for miscarriage. Other risk factors include older age, previously miscarrying, and malnutrition. The most common cause of miscarriage in the first trimester is chromosomal abnormalities.

Read on to learn more about whether smoking can cause miscarriage, including the level of risk by trimester and information on quitting.

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It is unclear if smoking can directly cause a miscarriage on its own. This is because many different factors can contribute to miscarriage.

However, smoking is one factor that may raise the risk of miscarriage. When a person smokes, the chemicals in tobacco cross the placenta, exposing a fetus to harmful substances. This has a range of effects, including:

  • affecting how the placenta develops
  • damaging tissues
  • reducing the oxygen the fetus gets

Scientists disagree on the exact level of risk that smoking poses. A 2022 study argues that mistakes in previous research may mean current data is incorrect.

The researchers say that previous studies recorded intentional abortions as miscarriages in people who smoke, have a higher body mass index (BMI), and drink. This may have exaggerated the impact of these risk factors.

Some other risk factors for miscarriage include:

  • older age
  • high blood pressure
  • malnutrition
  • being significantly underweight or overweight
  • injury
  • drinking alcohol
  • consuming high amounts of caffeine
  • certain physical health conditions
  • certain genetic conditions

None of these risk factors guarantee a person will have a miscarriage — they only elevate the risk.

Exposure to cigarette smoke at all stages of pregnancy can damage the placenta, increasing the risk of miscarriage. However, the overall risk of miscarriage varies by trimester.

First trimester

The risk of miscarriage is generally highest in the first trimester, with 80% of all pregnancy losses occurring in the first 3 months. Smoking may increase the risk further.

Tobacco smoke directly exposes a fetus to harmful chemicals. As the placenta develops late in the first trimester and beyond, it may also damage the placenta, increasing both the risk of miscarriage and negative pregnancy outcomes.

Second trimester

The rate of miscarriage is generally much lower in the second trimester than in the first.

Miscarriages can take place up until week 20 of pregnancy, which is halfway through pregnancy. After this point, the death of the fetus is known as a stillbirth.

A 2021 study compared the stillbirth rates in people who reported smoking, drinking, or neither after the first trimester of pregnancy. Among pregnant people who did not smoke or drink, the stillbirth rate was 0.4%. People who drank and smoked had a stillbirth rate of 1.5%, and for those who only smoked, the stillbirth rate was 0.8%.

Third trimester

Miscarriages do not happen in the third trimester. However, smoking can still raise the risk of other complications during late pregnancy and childbirth and in the health of the newborn.

People who smoke are more likely to experience preterm birth. The baby is also more likely to have a low birth weight. According to the Centers for Disease Control and Prevention (CDC), 1 in 5 babies born to parents who smoked during pregnancy have a low birth weight.

Smoking during pregnancy also has links to:

  • birth defects
  • health conditions in the newborn
  • a higher risk of death, such as from sudden infant death syndrome (SIDS)

Below are some answers to some frequently asked questions about smoking and miscarriage.

Can passive smoking cause a miscarriage?

Passive or secondhand smoke can raise the risk of a miscarriage. A 2021 review found a link between paternal smoking and miscarriage risk.

The study includes research looking at smoking in the preconception period. These studies suggest that paternal smoking before conception — independent of maternal smoking — could alter the development of the pregnancy by damaging the sperm’s DNA.

Can quitting smoking cause miscarriage?

There is no evidence that quitting smoking causes miscarriage. Quitting smoking offers both immediate and long-term health benefits.

When is it too late to stop smoking while pregnant?

It is never too late to stop smoking. As soon as a person stops smoking, the developing fetus no longer experiences smoke exposure. This can reduce the risk of health complications for the parent and their pregnancy.

Quitting smoking can be challenging, but help is available. The CDC offers a free helpline that can provide advice and support at 1-800-QUIT-NOW (1-800-784-8669)

A doctor can also discuss strategies for quitting smoking, including the risks and benefits of nicotine replacement therapy and other medications. A combination of strategies, such as therapy, medication, and lifestyle changes, is often most effective in helping people quit.

Smoking raises the risk of several complications during pregnancy, both for the developing fetus and the parent. This includes miscarriage and stillbirth, as well as birth defects, preterm labor, and more.

Even if a person has smoked during pregnancy, it is never too late to quit. The health benefits begin accumulating immediately. If a person is struggling, they can speak with a medical professional for help or contact a support organization for advice.