3.7 Pregnancy and smoking

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3.0 Background

3.1 Tobacco—a leading preventable cause of death and disease

3.2 Cardiovascular diseases

3.3 Lung cancer

3.4 Respiratory diseases

3.5 Other cancers caused by or associated with smoking

3.6 Reproductive health and smoking

3.7 Pregnancy and smoking

3.8 Infant health and smoking

3.9 Increased susceptibility to infection in smokers

3.10 Eye diseases

3.11 Dental diseases

3.12 Gastrointestinal diseases

3.13 Bone density and risk of fractures

3.14 Effects of smoking on the skin

3.15 Smoking and complications in medical treatment

3.16 Smoking and diabetes

3.17 Poorer levels of general health

3.18 Smoking, motor vehicle crashes and other injuries

3.19 Burns and fires caused by tobacco use

3.20 Tobacco poisoning

3.21 Health effects for younger smokers

3.22 Genetic influences on tobacco-caused disease

3.23 Smoking, dementia and cognitive decline

3.24 Lung disease, smoking and occupational exposures

3.25 Air pollution, cigarette smoking and ill health

3.26 Health effects of smoking brands that claim to deliver lower levels of tar, nicotine and carbon monoxide

3.27 Health effects of smoking tobacco in other forms

3.28 Health 'benefits' of smoking?

3.29 Morbidity (ill health) attributable to tobacco-caused disease

3.30 Deaths attributable to tobacco by disease category

3.31 Morbidity and mortality due to tobacco-caused disease and socioeconomic disadvantage

3.32 Health effects of smoking other substances

3.33 Health effects of chewing tobacco, and of other smokeless tobacco products

3.34 Public perceptions of tobacco as a drug, and knowledge and beliefs about the health consequences of smoking

3.35 Health benefits of cessation

3.36 The global tobacco pandemic

Acknowledgments

References

Smoking has a negative impact on the health of both the mother and the unborn child. Oxygen supply to the baby is compromised because of the oxygen-reducing effects of carbon monoxide in cigarette smoke. Blood flow to the uterus, placenta and foetus is also affected, due to nicotine's constricting effect on the uterine and umbilical arteries.5 Nicotine is found in foetal blood, amniotic fluid and breast milk5 and has a direct effect on foetal heartbeat and breathing movements.43 Other toxins from tobacco smoke also reach the foetus. Cadmium, a carcinogen, accumulates in the placenta and has been detected in umbilical cord blood.5

Smoking affects the healthy development and function of the umbilical cord and placenta, and causes abnormalities or insufficiencies that can lead to serious complications for the success of the pregnancy and the safe delivery of the baby. Premature rupture of the membranes (breaking of the amniotic sac before the onset of labour), placenta previa (when the placenta is attached to the uterine wall close to or over the cervix), and placental abruption (premature separation of the placenta from the wall of the uterus) are all caused by smoking.5

Smoking is associated with a greater likelihood of ectopic pregnancy (the implantation of a fertilised egg occurring outside the uterus; usually in the fallopian tubes). This may occur because nicotine slows down the movement of the fertilised ovum in the fallopian tubes, or because smokers have a higher risk of developing pelvic inflammatory disease, which is also associated with ectopic pregnancy.5

Women who smoke may also be at higher risk of spontaneous abortion or miscarriage (the involuntary termination of a pregnancy prior to 20 weeks of gestation).5 Because many miscarriages occur too early to be recognised and confirmed, and miscarriage can be caused by a number of preconditions, exposures or events, spontaneous abortions are difficult to study. However there is evidence that smoking has a role in promoting miscarriage, and many of the constituents of cigarette smoke are potentially toxic to the developing foetus, including lead, nicotine, cotinine, cyanide, cadmium, carbon monoxide and polycyclic aromatic hydrocarbons.5

Maternal smoking is associated with an increased risk of stillbirth (foetal death after 28 weeks' gestation) and neonatal mortality (death of an infant within the first 28 days of life).5 Data from the Australian Institute of Health and Welfare's National Perinatal Statistics Unit show that in 2003, babies born to mothers who smoked during pregnancy had a 50% greater risk of perinatal death[3] than babies of non-smoking women.44 About one third of perinatal deaths in the UK are thought to be attributable to smoking.45

Smoking is also a cause of premature birth and shortened gestation.5 Australian data show that in 2003, babies born to mothers who smoked in pregnancy had a 60% higher risk of preterm birth than babies of non-smoking mothers.44

Smoking in pregnancy also causes restricted growth and low birthweight in the infant. Intrauterine growth retardation (IUGR) is reduced foetal growth during gestation. Babies born with low birthweight have a higher risk of subsequent illness, death, and longer-term poor health outcomes through childhood and adult life.5 Babies born to smokers weigh on average about 200g less than babies born to non-smokers.5 Australian data show that babies of women who smoke during pregnancy are twice as likely to be of low birthweight (defined as weighing less than 2500 grams) compared to babies whose mothers are non-smokers, and are also more likely to be admitted to special care nurseries or neonatal intensive care units.44 In Australia in 2004?05, it is estimated that about 14% of all deaths due to low birthweight were attributable to tobacco use in pregnancy.7 Women who quit smoking early in their pregnancy have babies of similar weights to those of non-smokers.5

Research over the years concerning the possibility of an elevated risk of birth defects in general among infants born to smokers has been inconclusive, although positive associations have consistently been reported for smoking and cleft palate.5 A large, recent study of the US Natality Database has shown an apparent association between smoking and increased risk of congenital digital anomaly (abnormal number or formation of fingers). This finding awaits further investigation.46

Australian research has found that in 2005, about 17% of women smoked during pregnancy. The likelihood of smoking during pregnancy was higher in teenagers, among women in disadvantaged circumstances, and in Indigenous women47—see Chapter 1, Section 1.10.1.

Exposure to secondhand smoke during pregnancy is also a cause of reduced infant birthweight, and is associated with other health problems for the developing foetus.5, 48 See Chapter 4, Section 4.9 for further information.

3.7.1 Breastfeeding and smoking

Breastfeeding has wide-ranging health benefits for both baby and mother. For example, babies who are breastfed gain better levels of immunity to infectious disease,15 and women who have breastfed have a reduced risk of developing breast cancer, and possibly ovarian cancer.49

There is consistent evidence that women who smoke are less likely to breastfeed their infant and are more likely to wean their child earlier than mothers who do not smoke, even after adjusting for other influences on the decision to breastfeed, such as socioeconomic factors. Tobacco smoke appears to have a direct negative effect on milk quality, as well as the quantity produced. It is thought that nicotine may affect the activity of prolactin, a hormone essential for milk production.15, 41