3.8 Child health and maternal smoking before and after birth

Last updated: February 2020 
Suggested citation: Greenhalgh, EM, Ford, C, & Winstanley, MH. 3.8 Child health and maternal smoking before and after birth. In Greenhalgh, EM, Scollo, MM and Winstanley, MH [editors].  Tobacco in Australia: Facts and issues. Melbourne: Cancer Council Victoria; 2020. Available from  http://www.tobaccoinaustralia.org.au/chapter-3-health-effects/3-8-chid-health-and-maternal-smoking

 

Smoking during pregnancy is the most common preventable risk factor for pregnancy complications (see Section 3.7),1 and can also impact child health in a myriad of ways with potential lifelong consequences. During pregnancy, a foetus can be exposed to tobacco compounds via a pregnant women smoking or being exposed to secondhand smoke.2, 3 Following birth, infants may be exposed to tobacco compounds in breastmilk,4, 5 parental secondhand smoke in the home,3 to thirdhand smoke in household dust and indoor surfaces,6 and to an increased bacterial load carried by a parent or carer who smokes.7-9 Both prenatal and postnatal exposure can contribute to several health conditions in children.2, 3 The mechanisms underlying the adverse health effects of maternal smoking during pregnancy on the child remain poorly understood, although recent evidence suggests that epigenetics (i.e., changes in gene expression) most likely plays a role.10 Delineating the impact of each route of exposure in the causation of disease can sometimes be difficult, particularly for rarer conditions such as birth defects and childhood cancers.

This section summarises research on the association between prenatal smoking and:

It also summarises evidence on:

The link between parental smoking and development of childhood cancers is discussed in Chapter 4 Section 4.17.9.

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.11, 12 See Section 4.16 for further information.

3.8.1 Foetal growth and birthweight

Smoking in pregnancy causes restricted growth and low birthweight in the infant.11 ,13 Babies born with low birthweight have a higher risk of subsequent illness, death and longer-term poor health outcomes through childhood and adult life.11 Low birthweight is associated with heart disease, type 2 diabetes, high blood pressure and being overweight in adulthood.14-16

Babies born to smokers weigh, on average, about 150g to 200g less than babies born to non-smokers.11 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 g) compared to babies whose mothers are non-smokers. They are also more likely to be admitted to special care nurseries or neonatal intensive care units.17 , 18 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.19  

The effect of maternal smoking on low birthweight is largely due to intrauterine growth retardation (reduced foetal growth) and to a lesser extent shortened gestation. Reduced foetal measurements are apparent from the second trimester onwards. 20 Growth retardation is likely to be caused by chronic mild oxygen deprivation in the foetus from exposure to carbon monoxide, with a more minor role played by the effects of smoking on the placenta leading to nutritional deficiency of the foetus.2 The effects of smoking on birthweight appear to be stronger among older pregnant women and in women who have particular genotypes for drug-metabolising enzymes. The risk for low birthweight increases with the number of cigarettes the mother smokes per day.2 , 13 However, some research indicates that birthweight declines far more sharply at low levels of exposure, such as that experienced by women exposed to secondhand smoke and possibly by women who smoke a low number of cigarettes per day.21-25 This may help account for the observation that the benefits of cutting down the number of cigarettes smoked per day on birthweight are considerably smaller than for complete smoking cessation.4,24,26

Women who stop smoking early in their pregnancy have babies with similar birthweights to babies of non-smokers. Even women who stop before their third trimester can avoid much of the effect of smoking on birthweight. 11 ,20,27

3.8.2 Perinatal and infant death

3.8.2.1 Stillbirth

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).11,28 This effect appears to be dose-response, such that the odds of stillbirth increases with the heaviness of smoking.28,29 In 2015 and 2016 in Australia, perinatal deaths (i.e., deaths of babies of at least 20 weeks gestation or with a birthweight of at least 400 grams) were more common among babies of women who smoked throughout pregnancy compared to those who did not (9.4 and 6.0 deaths per 1,000 births, respectively). Perinatal deaths of normally-formed singleton babies near term (at least 36 weeks gestation) were also more likely among babies born to women who reported smoking during pregnancy compared with women who did not (2.4 and 1.2 deaths per 1,000 births, respectively).30

Proposed mechanisms by which smoking increases perinatal mortality include complications of pregnancy (abruption, placenta previa), preterm delivery, premature and prolonged rupture of the membranes (“water breaking”), and through physiologic responses of the foetus and newborn to stress.31

3.8.2.2 Sudden infant death syndrome

Sudden infant death syndrome (SIDS) is the sudden, unexplained, unexpected death of a child before one year of age.11 Smoking has been established as a cause of SIDS, whether the baby has been exposed to smoking before birth or in the home following birth.11 The biological pathway remains uncertain, but may be due to the effects of chronic oxygen deficiency on the development of the central nervous system and other neurotoxic effects of tobacco smoke on the foetal brain.11 Neurochemical changes to the cardiorespiratory control centres of the brainstem can result in changes in the development of respiratory control. Several studies have linked smoking during pregnancy to alterations in breathing patterns, ventilatory responses, and arousal responses in infants. 11, 32

For information on secondhand smoke and SIDS see Section 4.17.2

3.8.3 Birth defects

A large meta-analysis of studies published between 1959 and 2010 found that maternal smoking is associated with an increased risk for limb reduction defects; oral clefts; clubfoot; defects of the eyes; and defects of the gastrointestinal system, especially gastroschisis and abdominal hernia. More modest associations were found for digit anomalies (abnormal number or formation of fingers); cryptorchidism (undescended testes); and defects of the heart and musculoskeletal system, including craniosynostosis (premature fusing of the skull bones).33 A more recent meta-analysis found significant positive associations between maternal smoking during pregnancy and birth defects in the cardiovascular system; digestive system; musculoskeletal system; and face and neck system. Heavier smoking was associated with a greater likelihood of congenital malformations.34 Another meta-analysis estimated that smoking during pregnancy may lead to a 10% relative increase in the risk of congenital heart defects on average.35

The US Surgeon General’s report (2014) concluded that maternal smoking in early pregnancy causes orofacial clefts, and that maternal smoking is associated with other defects such as clubfoot, gastroschisis (the guts protruding through an opening in the abdominal wall), and atrial septal heart defects.31 Proposed mechanisms for oral clefts include the alteration of embryonic movements in early pregnancy that are important to the development of the organ systems, reduced supply of essential nutrients (such as vitamins and folate) for embryonic tissues, oxygen deficiency, and DNA damage. Mothers and babies with certain genotypes may be more susceptible to damage from tobacco smoke. Further work is needed to establish the mechanism. Studies also support an increased risk of oral clefts with paternal smoking, although it is not clear whether this is due to exposure of the mother to secondhand smoke or if it is due to the effects of tobacco smoke on sperm.2

3.8.4 Colic

A few studies have reported an association between maternal smoking, both during and after pregnancy, and infantile colic or excessive crying.36, 37 Infantile colic is characterised by the frequent sudden fits of irritability, inconsolable crying and screaming accompanied by clenched fists, drawn-up legs and a red face. It occurs in the first weeks after birth and usually resolves by four months of age.36 One study suggests that maternal smoking may be linked to colic through gastrointestinal tract dysregulation. More research is needed to confirm this theory.36

3.8.5 Respiratory health

Maternal smoking during pregnancy causes reduced lung function in infants, and may also cause an increase in the number of lower respiratory tract illnesses, including wheezing, during infancy.2, 38, 39 The effects of maternal smoking in utero may also be related to an increased risk of impaired lung function in childhood and adulthood.11 Australian research suggests that infants born to women who have smoked during pregnancy have weakened innate immune defences, and develop their acquired immune system more slowly than infants of non-smoking mothers. This may explain why infants of smokers are more prone to be asthmatic and to develop respiratory infections40 While smoking during pregnancy may increase the risk of wheezing illnesses in infants,11 the potential role of prenatal tobacco exposure as an independent cause of asthma is still unclear.3 In Australia in 2017, 13% of all deaths due to lower respiratory infections in babies less than one year of age were attributable to exposure to tobacco.41   

Infants living with smokers are also more likely to experience a range of respiratory symptoms and chest illnesses.3 These findings are discussed in greater detail in Section 4.17.

3.8.6 Childhood allergies and skin disease

The evidence is uncertain regarding the effect maternal smoking during pregnancy has on risk of allergic sensitisation and atopic disease, including allergic symptoms, eczema, rhinitis and dermatitis.3 A large Danish study found that prenatal tobacco exposure may increase the risk of paediatric psoriasis.42  

3.8.7 Neurodevelopment

Investigating the impact of maternal smoking on the cognitive and behavioural development in infants and children is difficult as many genetic and environmental factors can affect outcomes.2 While various studies have found an association between smoking during pregnancy and poorer outcomes in children, including for impaired learning and memory, lowered IQ, cognitive dysfunction, later childhood conduct problems, substance use, and early adult criminality, other studies report no association and the problems of inadequate study design.43

The US Surgeon General concluded in 2014 that maternal prenatal smoking increases the risk of disruptive behavioural disorders, particularly attention deficit hyperactivity disorder, among children.31 More recent reviews have similarly found an association between prenatal smoking and childhood ADHD,44, 45 and behavioural problems,46 and a 2019 meta-analysis found that, in the first year of life, specific areas of neurobehavioural functioning are related to prenatal cigarette exposure: negative affect, attention, excitability, irritability, orientation, muscle tone, regulation, and difficult temperament.47 However, the Surgeon General’s report concluded that there is insufficient evidence to infer a relationship between maternal prenatal smoking and anxiety, depression, Tourette syndrome, schizophrenia, and intellectual disability among children.31

Smoking during pregnancy may also relate to poorer academic achievement in children.46 General assessments of children’s cognition and intelligence have been mixed. However, studies of children’s general verbal skills and specific language and auditory tests have found a more consistent association between smoking during pregnancy and children’s poorer performance on these tests.2

3.8.8 Cardiovascular disease risk

Several studies have examined the link between smoking during pregnancy and the development of cardiovascular risk factors in the child. Among other risk factors, maternal smoking during pregnancy is associated being overweight or obese in childhood,48-54 and in adulthood.55, 56 This effect appears to be independent of the effects of smoking on foetal growth, and is likely to be an effect of smoking in early pregnancy.48-51 Possible mechanisms are the effects of smoking on hypothalamic function affecting food intake and energy expenditure, or abnormalities in fat cells.49, 50 Maternal smoking may also affect the infant gut microbiota, which may be associated with child overweight.57

The evidence is unclear as to whether there is an increased risk of higher blood pressure in children born to women who smoked during pregnancy.58 However, limited research indicates that maternal smoking in pregnancy leads to impaired blood pressure regulation in infants59 and adverse lipid (cholesterol) profiles in adult offspring.60-62 Smoking throughout pregnancy is a risk factor for cardiovascular developmental changes, including aortic narrowing, in early childhood and adolescence.63, 64 One study found that the foetuses of smoking mothers are more likely to have lesions in the walls of the foetal artery and adjoining vessels, which are the initial stages of atherosclerosis (narrowing of the arteries by fatty deposits).65

3.8.9 Vision problems

A systematic review of smoking during pregnancy and vision difficulties in children published in 2015 found that most studies reported an association between active or passive maternal cigarette smoking and an increased risk of adverse visual outcomes in children. In particular, there were higher rates of strabismus (crossed eyes), refractive errors and retinopathy among children of women who smoked during pregnancy.66 A meta-analysis similarly supported the findings that maternal smoking during pregnancy was associated with a significantly increased risk of offspring strabismus.67 A meta-analysis also concluded that maternal smoking is a risk factor for childhood hyperopia (farsightedness) and amblyopia (lazy eye).68

3.8.10 Physical development

Studies into the possible effects of smoking during pregnancy on subsequent physical growth of children have been mixed. Where differences have been found between children of smokers and non-smokers, they have generally been small. More research is needed.2, 11

3.8.11 Puberty and fertility

Several recent meta-analyses suggest that prenatal tobacco smoke exposure may decrease the age of menarche of girls.69, 70 Limited research also suggests that smoking during pregnancy may affect reproduction in female offspring. It is associated with a smaller uterus, a reduced number of somatic cells (which are necessary for egg survival), and slightly lower fertility in female offspring.2, 71-73 Several studies suggest that smoking during pregnancy may affect the reproductive development of male offspring, increasing the risk for lower sperm counts and quality, lower fertility, smaller testicles, cryptorchidism (undescended testes) and hypospadias (a penis abnormality).2, 33, 74-80

3.8.12 Nicotine dependence

Evidence is emerging that suggests that exposure to nicotine in utero predisposes an individual to a greater likelihood of nicotine dependence later in life, independent of socio-economic and other factors that influence uptake of smoking.81 It is possible that this may occur by nicotine having a direct effect on the developing foetal brain, causing permanent abnormalities in neurotransmitter regulation.81, 82 Other research, while confirming that offspring of women who smoked during pregnancy are more likely to become smokers in early adolescence, suggests that environmental influences on smoking uptake such as the mother’s current smoking status and peer group behaviour are stronger predictors.83

3.8.13 Breastfeeding and smoking

Nicotine is found in the breast milk of mothers who smoke, and can therefore be a key source of infant exposure to tobacco compounds among breastfed infants.84, 85 Cotinine, one of the main metabolites of nicotine, is found in the urine of breastfed infants of smokers, as well as in the urine of infants who are exposed to secondhand smoke.86 One study found that the amount of cotinine present in the urine of infants breastfed by smoking mothers was ten times higher than that found in bottle-fed infants whose mothers smoke.87 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. 4, 5 Nicotine absorbed by infants through breast milk can produce short-term symptoms such as restlessness, insomnia, nausea, vomiting, diarrhea and rapid pulse, and may affect infants’ autonomic cardiovascular control and sleeping patterns. 86, 88 While babies who are breastfed gain better levels of immunity to infectious disease, particularly against respiratory and ear infections associated with secondhand smoke exposure,4, 89-92 one study found that the protective effect of breastfeeding on the onset of respiratory allergy in children from birth until five years appears to be lost when their mothers smoke.93 Studies have also found long-term effects of exposure to nicotine in breast milk.84 One review found that the adverse effects of maternal nicotine on breastfed infants include: reduction of iodine supply to the infant; histopathological damage in the liver and lung; intracellular oxidative damage; reduction of pancreatic ß cells; decreased glucose tolerance; increased body weight after weaning from maternal addiction, and hyperleptinemia.94

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.85, 95 This effect persists even after adjusting for other influences on the decision to breastfeed, such as socio-economic factors. 4, 5 Women who choose to breastfeed and smoke should be informed about harmful chemicals contained in cigarettes that can be secreted into breast milk and should be strongly encouraged to quit94 (see Section 7.11). However, as nicotine has a short half-life in milk of about two hours, breastfeeding mothers who cannot quit can reduce the exposure of their baby to nicotine by prolonging the time between their last cigarette and breastfeeding.86

3.8.14 Health effects of paternal smoking

While there are clear links between maternal smoking during pregnancy and child health, recent research has started to examine the possible consequences of paternal smoking. Paternal smoking may damage sperm DNA and alter the expression of genes in the offspring (see Section 3.6.2), which may then increase the genetic disease burden in children.96-98 One review estimated that, with even a 25% increase in sperm mutation frequency caused by exposure to tobacco smoke, for each generation there will be millions of smoking-induced mutations transmitted from fathers to offspring.99

Studies have found associations between paternal smoking, birth defects and childhood cancers.97 A recent meta-analysis of observational studies found an association between paternal smoking before conception or during pregnancy and an increased risk of childhood acute lymphoblastic leukemia.100 A French study found a weak association between paternal smoking in the year before the child's birth and childhood brain tumours.101 Paternal smoking has also been associated with lower sperm counts in sons, independent of the level maternal nicotine exposure during the pregnancy.102 Preliminary research suggests that paternal smoking at conception may be a risk factor for ADHD in the offspring.103 While some research has found an association between early uptake of smoking by fathers and obesity in their sons,104 others have found no such relationship.105 Early paternal smoking may also be associated with asthma risk in offspring.106

3.8.15 Health effects of grandparents’ smoking

As with paternal smoking, recent studies have explored the possible role of grandparents’ smoking in grandchildren’s health outcomes, via alteration of epigenetic programming that affects gene expression. Several studies have found an increased risk of asthma in the grandchildren of grandmothers who smoked whilst mothers were in utero.106-109 One found a higher risk among grandchildren of grandmothers who smoked more heavily (i.e., a dose-response relationship), independent of maternal smoking.107 Birth weight may also be associated with the grandmother’s smoking behaviours during pregnancy.110-112

Grandparents’ smoking may also affect grandchildren’s health by exposing them to smoking secondhand smoke—see Section 4.17. A systematic review of grandparents’ influence on grandchildren’s cancer risk factors found that, in the tobacco studies reviewed, grandparents smoked around grandchildren, did not comply with parents’ wishes regarding secondhand smoke, and modelled behaviour which could be expected to lead grandchildren to taking up smoking. Grandparents who smoked could therefore adversely affect their grandchildren’s risk of cancer in multiple ways.113

 

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References for Section 3.8

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