Is secondhand smoke safe during pregnancy?

What does the evidence say about secondhand smoke during pregnancy?

1. Breathing in someone else's cigarette smoke during pregnancy is linked to a higher chance of preterm delivery and lower birth weight. 1
2. In a real-world study that measured tobacco smoke exposure through a pregnancy urine test, about 15 percent of babies were born with low birth weight, and heavier exposure tracked with smaller birth size. 2
3. A large 2026 review pooling more than a hundred studies on secondhand smoke found the effect on birth weight was dose-related, meaning more exposure meant a bigger drop. 3
4. Secondhand smoke exposure during pregnancy has also been tied to a higher chance of stillbirth. 1
5. A smoke-free home matters after delivery too, since ongoing secondhand smoke exposure raises a newborn's risk for sudden infant death syndrome. 1

Is secondhand smoke safe in each trimester?

• First trimester. This is a sensitive window for your baby's organs to form, so a smoke-free home is worth prioritizing now. If someone in your household smokes, ask them to step outside or into another room with the door closed.
• Second trimester. Exposure adds up over the whole pregnancy, not just one trimester, so keep the smoke-free rule going. This is also a good time to look into quitting support together if someone in your home is ready.
• Third trimester. A smoke-free home now also sets up a smoke-free start for your newborn, since ongoing exposure after birth raises SIDS risk. Get the household on the same page before the baby arrives.