For many years it appeared that women were in some way immune to the health effects of smoking, as it was overwhelmingly men who were developing lung cancer and other smoking related diseases. It has since become clear, however, that this was because men were smoking in far greater numbers and more heavily earlier this century than women (see Section 16.5 below). Women suffer all of the same disease processes caused by smoking as men do: heart disease, cancer, respiratory diseases and a wide variety of other ill effects (see Chapters 3 and 4 for detail). Additionally, women are at risk of developing a number of sex-specific problems due to smoking.
The risk of dying from a cardiovascular disease, including heart attack and stroke, is increased by at least four fold for women smokers over the age of thirty-five compared to non smokers who use oral contraceptives in the same age group. Comparing women over the age of thirty-five who smoke and use oral contraceptives to those in the same age group who do neither, the risk of dying from a cardiovascular disease is approximately nine fold.(105) carU.S. medical experts in this field recommend to physicians not to precsribe any oral contraceptives to women over 35 who smoke 15 or more cigarettes a day, and to warn lighter smokers of their higher risk. (106)
The contraceptive pill is one of the most common ways in which Australian women control their fertility. In 1995, almost 40% of women over the aged 18-49 years used the pill. In the middle age groups, pill use was still common with 31% of 35-39 year olds being current users, and the rates successively dropped for 40-44 year olds (10%).(107) Over a quarter of women aged 35-44 years smoked.(108)
Several studies have found that women who smoke have decreased fertility. Of these, one study has found that smokers have about 72% of the fertility of non-smokers and are 3.4 times more likely to take more than a year to conceive than non-smokers, all other factors being equal.(35) It has also been shown that female smokers show a reduced rate of fertility once contraceptive measures have ceased to be taken.(5,36) Studies are increasingly pointing towards a decreased ovulatory response in smokers and that the actual fertilisation and implantation of the zygote may be impaired in smokers.(5)
Research from Queensland has shown that smokers enrolled in IVF-ET (in vitro fertilisation and embryo transfer) and GIFT (gamete intrafallopian transfer) programs have a poorer outcome than non-smokers. Smokers produced fewer oocytes (immature eggs), had a pregnancy rate less than half that of non-smokers, and those smokers attaining a pregnancy had a markedly elevated risk of miscarriage. The authors conclude that the 'far greater chances of success for non-smokers justify vigorous attempts to convince [infertile couples] to stop smoking well before embarking upon assisted reproduction programs'.(37) Similar conclusions have emerged from international research.(38,39)
Smokers experience a greater prevalence of secondary amenorrhea (absence of menstruation), and irregularity of periods. Smokers are also more likely to experience unusual vaginal discharge or bleeding.(5) Smoking causes women to reach natural menopause one to two years earlier than non-smokers or ex-smokers.(9) This may be due to a toxic effect on the ovaries caused by smoke exposure,(5) or the significantly lower levels of oestrogens in smokers noted in many studies.(40)
Recent Australian research has shown cigarette smoking contributes to osteoporosis, an increase in bone fragility that accompanies aging.(41) Smoking reduces bone density, possibly through its effects on oestrogens. The study estimates that women who smoke 20 cigarettes a day through adulthood will have reduced their bone density by around 5 to 10% by the time they reach menopause, compared to non-smokers. This deficit in bone density is enough to increase the risk of fracture.
Women who smoke cigarettes have a greater risk of developing cancers of the cervix and vulvar. For cervical cancer, the relationship appears to be dose-responsive, with one study finding an 80% increased risk of developing the cancer among heavy smokers.(42) It is estimated that 19% of cervical cancer and 40% of vulvar cancer is caused by smoking.(43)
There is also evidence that passive exposure to tobacco smoke is a risk factor for the development of cancer of the cervix.(44) American research has shown that nicotine is present in the cervical fluid of non-smokers following exposure to passive smoking, although active smokers, who draw smoke directly into their lungs, have higher levels still.(45) The authors conclude that even low level exposure to environmental tobacco smoke may result in systemic effects.
Studies have estimated that between a quarter and a third of Australian women smoke during pregnancy.(46) Pregnant teenagers are also more likely to be smokers, reflecting coinciding patterns of high risk behaviour.(47,48)
Smoking affects the well-being of the foetus and the pregnant woman. According to the 1990 report of the US Surgeon General, 'Smoking is probably the most important modifiable cause of poor pregnancy outcome among women in the United States'.(9)
Nicotine, carbon monoxide and other toxic constituents of tobacco smoke cross the placenta readily, having a direct effect on the oxygen supply to the foetus, and the structure and function of the umbilical cord and placenta. A number of tobacco smoke constituents that cross the placenta are known carcinogens.(49) Nicotine has a direct effect on foetal heart rate and breathing movements.(50) Nicotine is also found in the breast milk of women who smoke.(50)
Spontaneous abortions and complications of pregnancy and labour all occur more frequently in smokers.(5) Smokers have a higher risk of ectopic (tubal) pregnancy(51,52,53) and have a greater tendency to deliver preterm.(5) Women who smoke during pregnancy have a 25 to 50% higher rate of foetal and infant deaths compared with non-smokers.(54)
Exposure by the mother to workplace passive smoking and paternal smoking has also been associated with lower birthweight, a higher risk of perinatal mortality,(55,56,57) and spontaneous abortion, particularly in the second trimester (mid three months) of pregnancy.(58)
Maternal smoking exerts a direct growth-retarding effect on the foetus, resulting in a decrease in all dimensions including length and circumference of chest and head.(5) Infants of smokers weigh on average 200 grams lighter than the infants of non-smokers,(5) and smokers have double the risk of having a low birthweight baby.(54)
The reduction in dimension and birthweight observed among the newborn of smokers has been described in the United States as 'fetal tobacco syndrome', and is defined as follows(54):
The mother smoked 5 or more cigarettes a day throughout the pregnancy.
The mother had no evidence of hypertension during pregnancy, specifically no preeclampsia and documentation of normal blood pressure at least once after the first trimester.
The newborn has symmetrical growth retardation at term, 37 weeks, defined as birthweight less than 2,500 grams, and a ponderal index (weight in grams divided by length) greater than 2.32. (Note: ponderal index is not a measure used in Australia).
There is no obvious cause of intrauterine growth retardation, that is, congenital malformation or infection.
Maternal smoking may predispose the child to respiratory illness. Parental smoking has been linked with decreased pulmonary function and asthma in children.(59) Smoking during pregnancy and in the infant's first year of life is considered one of the four major risk factors for sudden infant death syndrome ('SIDS' or 'cot death').(5,60,61,62,63) Research has suggested that smoking by either parent during pregnancy is associated with a higher incidence of all childhood cancers combined, but especially acute lymphocytic leukaemia and lymphoma. There may be an association between paternal smoking and brain cancer.(64) However at this stage, these findings are not consistent and should be considered as tentative.(65)
Other reported long term effects of maternal smoking on the infant include impairment of behavioural,(5,66) intellectual, and physical characteristics.(5) See also Chapter 4 for discussion of the health effects of passive smoking for infants and children. Readers requiring more information are referred in the first instance to references (67) and (68), both of which provide fully referenced, recent reviews of the medical evidence on the effects of passive smoking on pregnancy and infancy.