Does Smoking Cause Miscarriage? Risk and When to Quit

If you are trying to conceive, newly pregnant, or grieving a loss, the question does smoking cause miscarriage deserves a careful, kind answer. The research says smoking is associated with a higher risk of miscarriage, and that risk rises with the amount smoked. It also says that miscarriage is common, often unexplained, and rarely the result of any single choice. This guide sets out what the strongest evidence shows, what it cannot show, and what you can do from today, without blame.

The short answer: linked to higher risk, not a verdict on any one pregnancy

Smoking is associated with a higher chance of miscarriage. That is the finding of a large 2014 review on the question, and the NHS lists smoking among the things that may increase the chance of a miscarriage (NHS, Causes of miscarriage).

It is just as important to say what this does not mean. The NHS states that it is not always known what causes a miscarriage, and that it is often because there is a problem with the way the pregnancy develops. If you have had a miscarriage and you smoked, the research does not say you caused it. It says that, across many studies, smoking nudged the odds in the wrong direction.

The useful question is therefore not “what did I do?” but “what can I change now?” The answer is more hopeful than most people expect.

What the best evidence shows

The key source is a systematic review and meta-analysis published in the American Journal of Epidemiology in 2014 (Pineles et al., Systematic review and meta-analysis of miscarriage and maternal exposure to tobacco smoke during pregnancy). The authors reviewed the full text of 1,706 articles and included 98 that examined the association between active or passive smoking and miscarriage. The literature searches ran up to August 2011.

A relative risk of 1.23 means a 23% higher relative risk, which is not the same as a 23% chance of miscarriage. The paper notes that miscarriage is the most common complication of pregnancy, occurring in 12% to 26% of recognized pregnancies. So the baseline risk is already substantial for everyone, and smoking shifts it upward from there.

Two more findings matter. First, the risk was greater when smoking was defined as happening during the pregnancy in which the miscarriage was measured. Second, the risk of miscarriage increased with the amount smoked, at a 1% increase in relative risk per cigarette smoked per day. In plain terms, smoking less is better than smoking more, and not smoking is better still.

The authors concluded that the finding strengthens the evidence that women should not smoke while pregnant, and that all women of reproductive age should be warned that smoking increases the risk of miscarriage.

Watch: it is never too late to stop in pregnancy

In this short video from an NHS health partnership, two midwives and a tobacco dependency treatment advisor discuss the benefits of stopping smoking at any stage of pregnancy, according to the video description.

What the evidence cannot tell you

Honest reading of the research means three caveats.

It shows association, not blame

The Pineles review reports that the US Surgeon General’s 2004 report classified the evidence as suggestive but not sufficient to infer causation. The 2014 meta-analysis strengthened the picture considerably, but a population-level link cannot be turned into a verdict on one person’s pregnancy.

Most miscarriages happen early, with many contributing factors

The review notes that most miscarriages end early in pregnancy, at a time when a woman might not yet have learned she was pregnant. The NHS lists a range of things that may increase the chance of miscarriage, including age 35 or over, the baby’s father being aged 45 or over, certain medical conditions, caffeine, alcohol and obesity, alongside smoking. Smoking is one factor among many, and for many pregnancies the cause is simply not known.

There is a path forward

The NHS also says that most women who have had a miscarriage go on to have a successful pregnancy in the future. If you are grieving, your GP surgery or pregnancy unit can offer information and support, and so can the national charities the NHS lists.

Partners and secondhand smoke

If your partner or someone in your home smokes, the question is not only about you. In the Pineles review, secondhand smoke exposure during pregnancy increased the risk of miscarriage by 11%. Be careful with that number: the 95% confidence interval ran from 0.95 to 1.31, so it includes no effect at all. The evidence for secondhand smoke and miscarriage is therefore weaker than for active smoking.

The NHS is clearer about other harms. It says secondhand smoke can reduce your baby’s birthweight and increase the risk of sudden infant death syndrome, and that if your partner or anyone who lives with you smokes, their smoke can affect you and your baby before and after birth. It also notes you may find it harder to stop if someone around you smokes, so quitting together can help. Your partner can call the National Smokefree helpline on 0300 123 1044.

Nicotine replacement and vaping in pregnancy

Many people worry that quitting aids might be risky too. The NHS gives clear guidance:

• NRT. You can use nicotine replacement therapy during pregnancy if it will help you stop smoking and you are unable to stop without it. The NHS says NRT contains only nicotine and none of the damaging chemicals found in cigarettes, so it is a much better option than continuing to smoke.
• Patches. NRT patches should be used for no more than 16 hours in any 24-hour period, so remove the patch at bedtime. If you have pregnancy-related nausea and vomiting, patches may be a better solution.
• Prescription tablets. Stop smoking tablets such as varenicline or bupropion are not recommended during pregnancy.
• E-cigarettes. The NHS says that if using an e-cigarette helps you to stop smoking, it is much safer for you and your baby than continuing to smoke.

Speak to a midwife, GP, pharmacist or specialist stop smoking adviser before starting any of these. Our guide to quitting smoking while pregnant: safe methods covers the options in more depth.

Quitting at any point helps

The NHS says stopping smoking will help both you and your baby immediately, because carbon monoxide and other damaging chemicals clear from your body. It lists benefits including a lower risk of complications in pregnancy and birth, a lower risk of stillbirth, and a baby who is less likely to be born too early or with a low birth weight.

The timing message is encouraging: the sooner you stop smoking, the better, but even if you stop in the last few weeks of your pregnancy this will benefit you and your baby. For readers planning ahead, the same logic applies before conception. If you are preparing for fertility treatment, our guide on how to quit smoking before IVF explains why many clinics ask about it.

Withdrawal is the part that trips people up, especially while pregnant and tired. Knowing what is coming helps, so read through the stages of nicotine withdrawal and see how our body-recovery timeline, what happens to your body when you stop smoking, can keep you motivated.

For the bigger picture on pregnancy, see our articles on smoking during pregnancy risks and how to quit and smoking during pregnancy statistics. If you are also nursing or planning to, our guide on whether you can smoke while breastfeeding continues the story.

Getting free help to quit

The NHS says you are twice as likely to be successful at quitting if you get some support from a trained adviser. In the UK you can call the National Smokefree helpline on 0300 123 1044 (9am to 8pm Monday to Friday, 11am to 4pm Saturday and Sunday), or ask a midwife to refer you to an NHS stop smoking adviser.

NRT can be prescribed during pregnancy by a GP or an NHS stop smoking adviser, and can also be bought over the counter from a pharmacy. Elsewhere, ask your midwife, obstetrician or doctor about your local quitline and pregnancy programs.

Using iQuit while you quit

Quitting during pregnancy or while trying to conceive can feel lonely. iQuit is a free app on Google Play and the App Store that gives you tools for the daily work. The dashboard tracks your days smoke-free, cigarettes avoided and money saved. You can log each craving with its trigger and intensity, and when one hits, the SOS tools offer breathing exercises, a grounding exercise, craving surfing and a virtual cigarette. The health milestones timeline shows how your body recovers over time.

If you slip, streak shields and slip recovery are there to help you restart. iQuit is a support tool and is not medical care, so keep your midwife or doctor involved in decisions about NRT and your pregnancy.

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