What are the risks of smoking while pregnant?

Risks of Smoking During Pregnancy

Smoking during pregnancy is strongly associated with multiple severe adverse outcomes including increased risk of stillbirth, preterm birth, low birth weight, orofacial clefts, and long-term developmental issues for the child. 1

Major Maternal and Fetal Risks

Immediate Pregnancy Risks

• Smoking doubles the risk of delivering a baby with low birth weight and increases the risk of fetal death by 25% to 50% 1
• There is a clear dose-response relationship between maternal smoking and stillbirth risk, with heavier smokers (>1 pack per day) having an odds ratio of 1.43 (95% CI: 1.31-1.57) compared to nonsmokers 1
• Smoking during pregnancy causes premature rupture of membranes, placenta previa, placental abruption, and ectopic pregnancy 2
• Maternal smoking significantly increases the risk of preterm delivery, with a dose-response relationship observed 1

Birth Defects and Structural Abnormalities

• The evidence is sufficient to conclude that tobacco smoking in early pregnancy causes orofacial clefts 1
• Smoking during pregnancy is associated with reduced fetal growth and fetal growth restriction 2
• Infants born to mothers who smoke weigh significantly less than other infants, with studies showing consistent differences of 0.2-0.3 kg in birth weight 1

Long-term Developmental Effects

• Maternal smoking during pregnancy is associated with increased risk of the child being overweight at 3 years of age (adjusted OR: 1.33 [95% CI: 1.15-1.55]) 1
• Children of mothers who smoked during pregnancy have higher risk of psychiatric diagnoses through 18 years of age 1
• Academic performance is negatively affected, with children of mothers who smoked during pregnancy having 1.35 times higher odds of below-average performance at age 14 1
• Evidence suggests a causal relationship between nicotine exposure during fetal development and lasting adverse consequences for brain development 1

Mechanisms of Harm

• Nicotine and other tobacco toxins cross the placenta, directly exposing the developing fetus to harmful substances 1
• Maternal smoking causes reduced oxygen transport and delivery to fetoplacental tissues due to increased fetal carboxyhaemoglobin 1
• Nicotine-induced vasoconstriction reduces uteroplacental blood flow, potentially leading to fetal hypoxia 1
• Cigarette smoke contains thousands of chemicals, many of which are well-documented reproductive toxins (e.g., carbon monoxide and lead) 3

Cessation Benefits

• Quitting early in pregnancy provides the greatest benefit to the fetus 1
• Women who stop smoking during pregnancy have infants with birth weights similar to those of nonsmoking women (3.56 kg vs. 3.46 kg), compared to the significantly lower birth weights of infants born to women who continue smoking (3.16 kg) 1
• Cessation before or during early pregnancy can prevent preterm birth, low birthweight, and other adverse perinatal outcomes 1

Cessation Challenges

• Only about 20% of women successfully control tobacco dependence during pregnancy 1
• Addiction to nicotine prevents many pregnant women who wish to quit from doing so 3
• The safety and efficacy of nicotine replacement therapy during pregnancy remains limited, with nicotine classified as a Pregnancy Category D drug 4, 3

Clinical Approach

• Behavioral counseling interventions should be offered to all pregnant women who smoke 1
• For women in whom behavioral counseling does not work, careful consideration of other options may be needed, weighing risks against the substantial harms of continued smoking 1
• When considering pharmacotherapy, clinicians should consider the severity of smoking behavior and engage in shared decision making to determine the best treatment course 1
• Intermittent-use formulations of nicotine replacement therapy (gum, spray, inhaler) may be preferable to continuous-use formulations (patch) if used during pregnancy 3

Smoking during pregnancy represents one of the most significant modifiable risk factors for adverse pregnancy outcomes. The evidence clearly demonstrates that smoking cessation before or during pregnancy significantly improves outcomes for both mother and child.