Smoking and Pregnancy: Risks, Quitting Methods, and What Works

About 7-10% of pregnant women in the US smoke during pregnancy. The risks to the fetus are specific and well-documented: preterm birth, low birth weight, placental abruption, stillbirth and increased risk of sudden infant death syndrome (SIDS) [4]. A Cochrane review of 102 trials found that cessation interventions in pregnancy reduce the rate of low birth weight and preterm birth [1]. Quitting is the single most impactful thing a pregnant smoker can do for pregnancy outcomes. The evidence for that statement is not ambiguous.

What smoking does during pregnancy

The mechanisms are specific and well-characterized:

Carbon monoxide. Carbon monoxide from cigarette smoke crosses the placenta and binds to fetal hemoglobin with higher affinity than to adult hemoglobin. This directly reduces fetal oxygen delivery. The fetus is in a chronic state of mild hypoxia when the mother smokes. Fetal hemoglobin already binds oxygen more tightly than adult hemoglobin (this is how the fetus extracts oxygen from maternal blood); carbon monoxide exploits this same property, binding to fetal hemoglobin even more tenaciously than to the mother’s. The result is that the fetal blood carries less oxygen, and the oxygen it does carry is released less readily to fetal tissues.

Nicotine. Nicotine causes vasoconstriction in the uterine and placental blood vessels, further reducing blood flow and nutrient delivery to the fetus. The placenta is the fetus’s only source of oxygen and nutrition; anything that reduces placental blood flow restricts fetal growth. Nicotine crosses the placenta freely and is found in fetal blood, amniotic fluid, and breast milk.

Other toxins. The thousands of chemicals in cigarette smoke include known teratogens and carcinogens that cross the placenta. Polycyclic aromatic hydrocarbons, heavy metals (cadmium, lead), and hydrogen cyanide are all present in cigarette smoke and all cross the placental barrier. The fetal liver, which is still developing, is less capable of metabolizing and clearing these compounds than an adult liver.

The combined effect: restricted fetal growth, increased risk of premature delivery, and higher rates of complications. The mechanisms are not subtle, and they operate through every cigarette smoked.

Specific risks

Outcome	Risk increase from smoking
Low birth weight (<2,500 g)	1.5-2.5x increased risk
Preterm birth (<37 weeks)	1.2-1.5x increased risk
Placental abruption	1.4-2.4x increased risk
Stillbirth	1.2-1.6x increased risk
SIDS	2-3x increased risk
Certain birth defects	1.2-1.5x for cleft lip/palate, cardiac defects

These risks are dose-dependent: heavier smoking carries higher risk [4]. But even light smoking (1-5 cigarettes per day) carries measurable risk above non-smoking. The dose-response relationship is not linear for all outcomes. Carbon monoxide exposure, for example, does not decrease proportionally with the number of cigarettes smoked, because the body clears CO slowly (its half-life in blood is 4-6 hours). A woman who smokes five cigarettes spread through the day may have a persistently elevated carboxyhemoglobin level, not five times lower than a pack-a-day smoker’s.

The birth defect data, while less commonly discussed, is worth noting. A large meta-analysis found associations between maternal smoking and increased risk of cleft lip, cleft palate, congenital heart defects, and limb reduction defects [4]. The absolute risk for any individual defect remains small, but the increased relative risk is consistent across studies and biologically plausible given the teratogens in cigarette smoke.

Which cessation methods are recommended

Behavioral counseling is the first-line intervention. The Cochrane review found that psychosocial interventions (counseling, cognitive behavioral therapy, incentives) significantly increase quit rates in pregnancy and improve birth outcomes [1]. Incentive-based programs (providing financial rewards for verified abstinence) showed the strongest effects among behavioral approaches. The effect sizes are meaningful: women who receive structured cessation counseling quit at higher rates than those who receive standard prenatal advice, and their infants have higher birth weights on average.

The effectiveness of behavioral interventions in pregnancy is partly because pregnancy itself provides strong motivation. Many women who could not quit before pregnancy find it possible during pregnancy because the stakes have changed. Behavioral support during this window is not starting from zero; it is supporting a motivation that already exists and channeling it into an effective quit plan.

NRT is considered when behavioral support alone is insufficient. The evidence for NRT in pregnancy is less clear than in the general population. The SNAP trial, a large RCT of 1,050 pregnant women, found no significant difference in quit rates between nicotine patch and placebo [2]. This was a surprising result, and the most likely explanation involves pharmacokinetics: pregnant women metabolize nicotine roughly 60% faster than non-pregnant women. The standard 15 mg patch, designed for non-pregnant adult metabolism, may not deliver enough nicotine to meaningfully reduce cravings in a woman whose body is clearing nicotine at nearly twice the normal rate.

The Cochrane review of pharmacological interventions in pregnancy found that NRT may improve birth weight but the evidence on quit rates remains uncertain [3]. The birth weight finding is important: even when NRT does not produce a sustained quit, the replacement of cigarette nicotine with NRT nicotine eliminates the carbon monoxide and combustion product exposure, which may independently improve fetal growth.

Varenicline and bupropion are generally not recommended during pregnancy due to insufficient safety data. Neither has been studied in adequately powered pregnancy trials. The absence of evidence is not evidence of harm, but it means these treatments cannot be recommended when alternatives with better-characterized safety profiles exist.

NRT in pregnancy: the clinical position

Guidelines vary by country on NRT use in pregnancy:

• ACOG (US): NRT may be considered if behavioral interventions fail, after discussion of risks and benefits [5]
• NICE (UK): NRT is offered if the woman cannot quit with behavioral support alone; intermittent forms (gum, lozenge) are preferred over the patch
• General principle: NRT delivers nicotine without carbon monoxide and combustion products, making it safer than continued smoking

The preference for intermittent NRT forms over the patch in some guidelines reflects the concern that the patch provides continuous fetal nicotine exposure, while gum or lozenge provide intermittent peaks with periods of lower exposure between uses. The fetus experiences each peak and trough of nicotine, and the argument is that intermittent exposure with periods of clearance is preferable to continuous exposure, even if the total daily nicotine dose is similar. The evidence does not clearly demonstrate that this distinction matters for fetal outcomes, but the pharmacological reasoning is sound, and in the absence of definitive data, guidelines err on the side of caution.

The dose question is important and unresolved. If pregnant women metabolize nicotine 60% faster than the general population, the standard NRT doses may be subtherapeutic. A dose that does not adequately suppress cravings will not support cessation, which may explain the SNAP trial’s null result. Whether higher-dose NRT in pregnancy would be both more effective and still safe is a question that current evidence does not answer.

Timing of quitting

Quitting at any point during pregnancy provides benefit. The greatest benefit comes from quitting in the first trimester:

• Quitting before week 15 produces birth weight improvements similar to never-smokers
• Quitting in the second trimester still reduces preterm birth risk
• Quitting in the third trimester still reduces some risks, though some effects (fetal growth restriction) may already be established

The first trimester is when organogenesis occurs: the period when the fetus’s major organ systems are forming. The teratogenic risk from cigarette smoke is highest during this window. Quitting before or during the first trimester reduces birth defect risk to near-baseline levels [4]. This does not mean quitting later is pointless. Placental abruption risk, preterm birth risk, and SIDS risk are all reduced by quitting at any gestational age. The message is not “quit early or don’t bother.” It is “quit as early as you can, and know that quitting later still helps.”

Partner and household smoking

A pregnant woman who has quit but lives with a smoker continues to be exposed to carbon monoxide, particulate matter, and nicotine through secondhand smoke. This exposure is associated with reduced birth weight and increased respiratory risk in the infant, independent of maternal smoking status.

For households where the pregnant woman is quitting, the practical implication is that partner cessation or strict outdoor-only smoking by others in the household is part of the intervention. The pregnant woman cannot fully eliminate fetal smoke exposure if the household itself is a smoke-exposure environment. This is not a theoretical concern; it is a measurable effect that shows up in birth weight data.

Postpartum relapse

Relapse rates after pregnancy are high. Studies consistently find that more than half of women who quit during pregnancy resume smoking within six months of delivery [1]. The motivational context changes: the immediate, concrete stakes of pregnancy are replaced by the chronic, diffuse challenges of new parenthood, including sleep deprivation, stress, and returning to pre-pregnancy social contexts.

This is not a failure of character. It is a predictable pharmacological and behavioral outcome. The cravings that were managed during pregnancy by strong motivation return in a context where the motivation has shifted and the stress has increased. Cessation programs that extend through the postpartum period, not ending at delivery, have better long-term outcomes than those that treat pregnancy as the endpoint.

For the infant, continued cessation after delivery matters for SIDS prevention (SIDS risk is associated with postnatal smoke exposure in the home, not only prenatal exposure), for respiratory health (secondhand smoke is a major risk factor for infant respiratory illness), and for breastfeeding (nicotine transfers into breast milk, though breastfeeding while smoking is still considered preferable to formula feeding, because the benefits of breastfeeding outweigh the nicotine exposure in most analyses).

What this means if you’re deciding

If you are pregnant and smoking, the most effective first step is behavioral counseling, which your prenatal care provider can refer you to. Many states provide enhanced Quitline services for pregnant women, including more intensive counseling and sometimes NRT.

If behavioral support alone is not sufficient, discuss NRT with your prenatal care provider. The risk of continued smoking is well-established and substantial; the risk of NRT is uncertain but likely lower than continued smoking. The decision is not “NRT or nothing”; it is “NRT or continued cigarette exposure,” and the evidence favors the former.

Reduction is better than no change, but cessation is the goal. Even a few cigarettes per day expose the fetus to carbon monoxide and reduced blood flow.

Open questions

Whether higher-dose NRT is needed in pregnancy to compensate for accelerated nicotine metabolism has not been adequately studied. Whether e-cigarettes are a viable harm-reduction option during pregnancy is not established, and the evidence base is insufficient to support or refute their use. The safety of varenicline in pregnancy remains unknown due to lack of trial data. Whether the high postpartum relapse rate could be reduced by extending NRT through the postpartum period, rather than stopping at delivery, is an important practical question that has received limited attention in the trial literature.

A doctor or pharmacist can help choose the right approach for your health history. The Quitline (1-800-QUIT-NOW) provides free coaching and can sometimes supply NRT.