Smoking, Sex And Reproduction

Introduction

Cigarette smoking can affect women?s fertility; men?s fertility; sexual function in men; pregnant women's health; the health of an unborn child; and the health of young children. Most of the information below is sourced from the British Medical Association report: Smoking and Reproductive Life:

Fertility

Women who smoke take longer to conceive. Among smokers, the chances of conceiving fall by 10 ? 40 per cent per cycle. The greater the quantity of cigarettes smoked, the longer a woman is likely to take to achieve pregnancy. Even comparatively low levels of smoking can have a significant impact. An investigation involving almost 11,000 women in Denmark revealed 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. A British study found that both active and passive smoking was associated with delayed conception. Cigarette smoking can also affect male fertility: 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 semen of smokers have been found to reduce the motility of sperm. One study found that sperm damaged by smoking may also result in more couples having baby girls than boys. The researchers suggest that the sperm cells carrying the Y chromosome are more vulnerable to the toxins in cigarette smoke. Active and passive smoking also reduce the success rates of fertility treatment.

Male sexual impotence

Impotence, or penile erectile dysfunction, is the repeated inability to have or maintain an erection. Mounting evidence indicates smoking may cause male sexual impotence. A meta-analysis of studies published since 1980 found that 40% of impotent men were current smokers compared with 28% of men in the general population. Overall smoking increases the risk of impotence by around 50% for men in their 30s and 40s. ASH and the British Medical Association have calculated that around 120,000 UK men in this age group are needlessly impotent as a result of smoking.

Smoking and oral contraceptives

Women who use combined oral contraceptives are liable to increased risk of heart disease. Because the risk of heart disease in young women is low, the benefits of using the pill generally outweigh the risks for young women who do not smoke. Among pill-users who smoke, however, the risk of succumbing to a heart attack is 20 times higher. It is therefore important that all women who take the contraceptive pill be advised not to smoke.

Smoking and pregnancy

According to the Infant Feeding Survey of 2005, 32% of mothers in England reported smoking in the 12 months before or during pregnancy. Of these, 17% continued to smoke throughout pregnancy. Women who smoke in pregnancy are more likely to be younger, single, of lower educational achievement and in unskilled occupations. The IFS survey revealed that almost half (49%) of women who smoked before pregnancy managed to stop once they became pregnant. In December 1998, the Government set a target to reduce the percentage of women who smoked during pregnancy from 23% to 15% by the year 2010, with a fall to 18% by 2005.

Fetal growth and birth weight

Babies born to women who smoke are on average 200 grams lighter than babies born to comparable non-smoking mothers. Furthermore, the more cigarettes a woman smokes during pregnancy, the greater the probable reduction in birth weight. Recent research suggests that cigarettes can impede the flow of blood in the placenta which in turn restricts the amount of nutrients that reach the fetus. Low birth weight is associated with higher risks of death and disease in infancy and early childhood. The adverse effects of smoking in pregnancy are due mainly to smoking in the second and third trimesters. Therefore, if a woman stops smoking within the first three months of pregnancy, her risk of having a low‑weight baby will be similar to that of a non-smoker.

Spontaneous abortion

The rate of spontaneous abortion (miscarriage) is substantially higher in women who smoke. This is the case even when other factors have been taken into account.

Other complications of pregnancy

On average, smokers have more complications of pregnancy and labor which can include bleeding during pregnancy, premature detachment of the placenta and premature rupture of the membranes. Some studies have also revealed a link between smoking and ectopic pregnancy and congenital defects in the offspring of smokers. Studies have indicated that women who smoke are 1.5 - 2.5 times at risk of an ectopic pregnancy. The risk is even sizeable where comparatively few cigarettes are smoked. One study reported a sixty percent risk propensity of ectopic pregnancy amongst women who smoked as few as five cigarettes a day. Another study found women who reported a past sexually transmitted pelvic infection such as Chlamydia had a 3.4-fold increased risk for ectopic pregnancy compared to women to women who had never had such infections. Smokers were 3.9 times more likely to have an ectopic pregnancy than women who never picked up the habit, the authors report.

Perinatal mortality

Perinatal mortality (defined as still‑birth or death of an infant within the first four weeks of life) is increased by about one-third in babies of smokers. This is equivalent to approximately 1900 deaths per year in England and Wales. The increased perinatal mortality in smoking mothers occurs particularly among manual socio-economic groups and in groups that are already at high risk of perinatal death, such as older mothers or those who have had a previous perinatal death. More than one-quarter of the risk of death due to Sudden Infant Death Syndrome (cot death) is attributable to maternal smoking. Smoking during pregnancy has also been linked as a possible cause of cot death. The risk of cot death is trebled in infants whose mothers smoke both during and after pregnancy. The greater the quantity of cigarettes smoked, the higher the risk of cot death. Pre-term birth is a major clinical problem, accounting for about half of all neonatal deaths. Recent research in Sweden examined the relationship between maternal smoking and pre-term birth and found that, compared to nonsmokers, there was a two-fold increase in risk of preterm labour among moderate smokers, rising to two and a half times greater risk among heavy smokers.

Passive smoking and pregnancy

Non-smoking women exposed to other people?s tobacco smoke during pregnancy are more likely to have lower weight babies. Babies born to non-smoking women whose partners smoked weighed less than babies born to non-smoking couples. Moreover, women exposed to second-hand smoke in the workplace are also affected. A review of the evidence concluded that on average, infants born to women exposed to second-hand smoke during pregnancy are 40-50g lighter than those born to women who are not exposed. Other research suggests that non-smoking women who are exposed to second-hand smoke during their pregnancy are at increased risk of giving birth prematurely and may be at increased risk of spontaneous abortion (miscarriage).

Breast feeding

Research has shown that smoking cigarettes may contribute to inadequate breast milk production. In one study, fat concentrations were found to be lower in the milk from mothers who smoked and milk volumes were lower. In breastfeeding mothers who smoke, milk output is reduced by more than 250 ml per day compared with smoking mothers. Prolactin is vital for the initiation and maintenance of milk production by the mother. Breastfeeding women who smoke have lower levels of prolactin than those who do not smoke. Nicotine has been shown to hamper the production of prolactin. It is plausible that prolactin production in smoking mothers might be reduced, resulting in poorer milk supply and an increased likelihood of giving up breastfeeding earlier.

Health and long‑term growth

Infants of parents who smoke are twice as likely to suffer from serious respiratory infection than the children of non-smokers. Smoking during pregnancy can also increase the risk of asthma in young children. New research suggests that the increased risk of asthma and respiratory infections may be due to changes in biological receptors in the baby?s immune system that are responsible for recognising and fighting infections and bacteria. Other ill effects and disorders associated with smoking in pregnancy include an increased risk of infantile colic and cleft palate.

Smoking in pregnancy may also have implications for the long term physical growth and intellectual development of the child. It has been associated with a reduced height of children of smoking mothers as compared with non-smoking mothers, with lower attainments in reading and mathematics up to age 16 and even with the highest qualification achieved by the age of 23. There is also evidence that smoking interferes with a woman's hormonal balance during pregnancy and that this may have long-term consequences on the reproductive organs of her children.

Smoking and cervical cancer

Epidemiological studies have found that women who smoke have up to four times higher risk of developing cervical cancer than non-smokers and that the risk increases with duration of smoking. Studies have demonstrated biochemical evidence that smoking is a causal factor in cervical cancer. Cervical cancer is the leading cause of cancer death in women worldwide, with more than half a million new cases diagnosed annually. Smoking increases the risk of invasive cervical cancer two-to-three fold. In 2002, the International Agency for Research on Cancer (IARC) reviewed the large number of studies available and concluded that smoking is a cause of invasive (malignant) cervical cancer.

Smoking and the menopause

The natural menopause occurs up to two years earlier in smokers. The likelihood of an earlier menopause is related to the number of cigarettes smoked, with those smoking more than ten cigarettes a day having an increased risk of an early menopause. Stopping smoking may lower the risk of early menopause. While current smokers? risk of early menopause is twice that of non-smokers, in ex-smokers the risk is higher by just one-third. Research suggests that polycyclic aromatic hydrocarbons found in tobacco smoke can trigger premature egg cell death which may in turn lead to earlier menopause. Another study suggests that chemicals in tobacco smoke alter endocrine function which in turn affect the release of pituitary hormones. This endocrine disruption is thought to contribute to adverse outcomes including earlier menopause.