Pregnancy, Birth Weight and Fertility: Smoking Risks

This page is general information from Health Canada, not medical advice. If you are pregnant or planning a pregnancy, a midwife, doctor or pharmacist can help you choose how to quit.

How does smoking affect pregnancy and the baby?

Health Canada’s page on pre- and post-natal risks says babies born to mothers who smoked during pregnancy have a higher chance of low birth weight, meaning under 2.5 kg (5.5 lb), and that low birth weight raises the baby’s later risk of illness and premature death. Smoking or exposure to tobacco smoke in pregnancy is linked to a greater risk of preterm delivery, before 37 weeks, and of placental complications.

The page names two mechanisms. Nicotine can decrease blood flow through the placenta, which deprives the baby of oxygen and nutrients. Carbon monoxide can harm the central nervous system and slow growth. For scale, it reports that 5% of Canadian women aged 15 to 55 who had been pregnant in the previous five years smoked while pregnant in 2021.

What is the link to sudden infant death syndrome?

Health Canada’s SIDS page says infants whose parents smoked during pregnancy, and infants exposed to second-hand smoke after birth, face a higher risk, and that the risk rises with the number of cigarettes, the number of smokers in the home and how close the smoking is to the baby. It estimates that 14% to 16% of SIDS deaths in Canada in 2012 were caused by smoking. Cutting down lowers the risk and quitting lowers it further. The page notes that the exact cause of SIDS remains unknown.

Does smoking affect fertility?

Health Canada’s pages point to both partners. For women, its menstruation and menopause page says smoking brings menopause about one to two years earlier, a shorter reproductive window, and links smoking of more than a pack a day to irregular cycles. For men, the page on impotence says smoking can damage sperm cells, leading to fertility problems, and that cigarettes cause erectile dysfunction. Neither page gives a figure for how much smoking lowers the chance of conceiving, so we do not either.

Is it too late to quit once I am pregnant?

No. Health Canada says quitting before conception or early in pregnancy gives the greatest benefit to mother and baby, but quitting at any point still helps, and lowers the risk of a smaller-than-usual baby. Practical steps, including what is safe to use, are in our guide to quitting smoking while pregnant. Free counselling by province is on the free help page, and medication questions go to the quit medications guide.