Smoking and fertility

It is estimated that around one in six couples in the UK experiences problems in conceiving at some time. Several types of study provide information on the effects of smoking on fertility. Semen analysis can reveal abnormalities. Surveys of pregnant women can investigate the time taken to conceive. Studies of couples can compare those who conceive with those who do not. Finally, investigation of couples having fertility treatments can help to characterise differences in the quality of egg and sperm, fertilisation, implantation and early loss of embryos.

Smoking reduces fertility in both men and women. The fertility problems observed in smokers may result at least in part from alterations in sex hormone metabolism. Other effects may also contribute. Substances present in cigarette smoke have been found to be toxic to the testes and ovaries.

British Medical Association Smoking and reproductive life: The impact of smoking on sexual, reproductive and child health 12
have also found adverse effects of nicotine and cigarette smoke on the interaction of egg and sperm and the implantation of the fertilised egg

Semen quality and sperm damage

Smoking reduces the quality of semen: men who smoke have a lower sperm count than non-smokers, and their semen contains a higher proportion of malformed sperm By-products of nicotine present in the semen of smokers have been found to reduce the motility of sperm,and to affect their normal swimming patterns

Genetic material in sperm cells is damaged by smoking. For example, benzo[a]pyrene, one of the carcinogenic components of tobacco smoke, has been found to bind to DNA in sperm, inducing mutations. This damage can persist in embryos.

Delayed conception

Women who smoke take longer to conceive. Among smokers, the chances of conceiving are decreased by 10–40 per cent per cycle. The greater the number of cigarettes smoked, the longer a woman is likely to take to achieve pregnancy. However, even relatively low levels of smoking can have a substantial impact.

A study of almost 11,000 women in Denmark found that women who smoked between five and nine cigarettes a day were 1.8 times more likely than non-smokers to wait longer than 12 months to conceive.

Infertility

Infertility is usually defined as not having conceived after 12 months of unprotected sex. Smoking increases the risk of infertility: women who smoke are twice as likely to be infertile as non-smokers. This is true for both women attempting to become pregnant for the first time (primary infertility) and women who have read more