What are the risks of second-hand smoke exposure during pregnancy?

From the Guidelines

Second-hand smoke exposure during pregnancy poses serious risks to both mother and baby and should be avoided completely. When a pregnant woman breathes in second-hand smoke, harmful chemicals like carbon monoxide, nicotine, and other toxins enter her bloodstream and cross the placenta to the developing fetus. These exposures increase the risk of pregnancy complications including miscarriage, placental problems, preterm birth, and low birth weight. Babies exposed to second-hand smoke before birth have higher rates of birth defects, particularly heart defects, and may experience impaired lung development. After birth, these infants face increased risks of sudden infant death syndrome (SIDS), respiratory infections, asthma, and ear infections. The risks increase with the amount and frequency of exposure, with no safe level established.

Key Risks Associated with Second-Hand Smoke Exposure

• Increased risk of stillbirth, with a dose–response relationship demonstrated 1
• Increased risk of preterm birth, with a dose–response relationship demonstrated 1
• Reduced birth weight, with mean birth weight lower in tobacco smoke–exposed women compared with unexposed women 1
• Increased risk of asthma, wheezing, and asthma exacerbations in children 1
• Increased risk of SIDS, with the risk greater if both parents are smokers 1

Recommendations for Pregnant Women

• Avoid all smoke-filled environments
• Ask partners and family members not to smoke in the home or car
• Ensure complete smoke-free zones in living spaces
• Be aware of the risks of "third-hand smoke" - residue left on surfaces, furniture, and clothing that can contain harmful substances 1

From the Research

Risks of Second-Hand Smoke Exposure During Pregnancy

• Second-hand smoke exposure during pregnancy is associated with various adverse effects on pregnancy and fetal development, including spontaneous abortion, placental abruption, and reduced birth weight of the newborn 2.
• Children of mothers exposed to second-hand smoke have an increased risk of premature birth, low birth weight, sudden infant death syndrome, and respiratory diseases during infancy 2, 3.
• Second-hand smoke exposure increases the risk of infant stillbirth, congenital malformations, low birth weight, and respiratory illnesses 4.
• Exposure to environmental tobacco smoke (ETS) increases the risk of having night cough and respiratory infections (bronchitis, bronchiolitis, pneumonia), especially during the first 2 years of life 3.

Health Effects on the Foetus

• Smoking during pregnancy can cause changes in the development of the foetus, including changes in levels of enzymes, hormones, and expression of genes, micro RNAs, and proteins 5.
• Prenatal tobacco smoke exposure is associated with changes in the immune status, and is harmful to lung, heart, and blood vessels 5.
• Second-hand smoke exposure during pregnancy can lead to epigenetic effects that influence in utero gene expression and disease susceptibility 5.

Prevalence of Second-Hand Smoke Exposure

• The prevalence of daily second-hand smoke exposure during pregnancy ranges from 6% to 73% in low-income and middle-income countries 4.
• Second-hand smoke exposure in pregnant women closely mirrors WHO Global Adult Tobacco Survey male active smoking patterns 4.
• Daily second-hand smoke exposure accounts for a greater population attributable fraction of stillbirths than active smoking, ranging from 1% to 14% 4.