Asthma Management Handbook

Prenatal advice for women concerned about their children’s risk of developing asthma

Recommendations

Advise women not to smoke while pregnant, and support them to quit. Also advise women pregnant to avoid exposure to environmental tobacco smoke.

How this recommendation was developed

Adapted from existing guidance

Based on reliable clinical practice guideline(s) or position statement(s):

  • ASCIA 20091
  • RANZCOG 20172
  • RACGP 20143

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Advise pregnant women to avoid unnecessary paracetamol use.

Note: Paracetamol can be used if needed, according to guidelines for analgesia and management of fever in pregnancy.

How this recommendation was developed

Consensus recommendation following inconclusive literature search

Based on clinical experience and expert opinion after literature review yielded insufficient evidence for an evidence-based recommendation.

Key evidence considered:

  • Castro-Rodriguez et al. 20164
  • Cheelo et al. 20155
  • Dick et al. 20146
  • Eyers et al. 20117
  • Etminan et al. 20098
  • Koniman et al. 20079
  • Goksör et al. 201110
  • Bakkeheim et al. 201111
  • Shaheen et al. 201012
  • Shaheen et al. 201013
  • Shaheen et al. 200214
  • Garcia-Marcos et al. 200815
  • Perzanowski et al. 201016
  • Persky et al. 200817
  • Rebordosa et al. 200818
  • Kang et al 200919

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Prescribe antibiotics for pregnant women as indicated and where a clinical benefit is likely, but avoid unnecessary use.

How this recommendation was developed

Consensus

Based on clinical experience and expert opinion (informed by evidence, where available), with particular reference to named source(s):

  • Zhao et al. 201520

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Advise pregnant and breastfeeding women to aim for a healthy, balanced diet rich in fibre, vegetables and fruit, for general benefits and possible protection against wheeze in children, although healthy eating is not proven to prevent asthma and allergies in children.

How this recommendation was developed

Adapted from existing guidance

Based on reliable clinical practice guideline(s) or position statement(s):

  • ASCIA 201621
  • RANZCOG 201422

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Do not routinely recommend, as a strategy for preventing asthma in children, that pregnant women attempt to avoid house dust mite or other inhaled allergens.

Note: Dust mite avoidance is onerous and avoidance measures during pregnancy are not effective in reducing children’s risk of developing asthma.

How this recommendation was developed

Adapted from existing guidance

Based on reliable clinical practice guideline(s) or position statement(s):

  • ASCIA 201621
  • ASCIA 20091

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Do not recommend dietary restrictions during pregnancy.

Note: Dietary restrictions during pregnancy do not prevent asthma in children, and may be harmful to the mother and foetus.

How this recommendation was developed

Evidence-based recommendation

Based on literature search and formulated by multidisciplinary working group

Key evidence considered:

  • Netting et al. 201423
  • Kramer & Kakuma. 201224

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Do not recommend, as a strategy for preventing asthma in children, that pregnant women take prebiotic dietary supplements.

Note: Prebiotic supplements have not been shown to reduce children’s risk of developing asthma.

How this recommendation was developed

Consensus recommendation following inconclusive literature search

Based on clinical experience and expert opinion after literature review yielded insufficient evidence for an evidence-based recommendation

Key evidence considered:

  • Osborn et al. 201325

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Do not recommend, as a strategy for preventing asthma in children, that pregnant women take probiotic dietary supplements.

Note: Probiotic supplements are not effective in reducing children’s risk of developing asthma.

How this recommendation was developed

Evidence-based recommendation

Based on literature search and formulated by multidisciplinary working group

Key evidence considered:

  • Zuccotti et al. 201526
  • Azad et al. 201327
  • Elazab et al. 201328
  • Abrahamsson et al. 201329
  • Simpson et al. 201530

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Advise pregnant women and women planning pregnancy to follow current national guidelines for Vitamin D supplementation.

Note: Current RANZCOG guidelines for vitamin and mineral supplementation during pregnancy recommend vitamin D supplementation for all pregnant women and blood level testing is recommended for those who may be vitamin D-deficient.

How this recommendation was developed

Consensus

Based on clinical experience and expert opinion (informed by evidence, where available), with particular reference to named source(s):

  • Vahdaninia et al. 201631
  • Wolsk et al. 201732
  • Litonjua et al. 201633, 34
  • Wolsk et al. 201735
  • Chawes et al. 201636

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Do not routinely recommend, as a strategy for preventing asthma in children, that pregnant women take supplementary vitamin A, vitamin E or fish oil.

How this recommendation was developed

Consensus

Based on clinical experience and expert opinion (informed by evidence, where available), with particular reference to named source(s):

  • Greenough et al. 201037
  • Best et al. 201638
  • Gunaratne et al. 201539
  • Klemens et al. 201140
  • Bisgaard et al. 201641
  • Best et al. 201642, 43
  • Toelle et al. 2013 44, 45

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More information

Overview of factors reported to increase or decrease children's risk of developing asthma

Many modifiable and non-modifiable factors have been associated with increased or decreased risk of asthma development in children.

Table. Risk factors and protective factors for developing asthma Opens in a new window Please view and print this figure separately: http://www.asthmahandbook.org.au/figure/show/117

Although many factors have been associated with increased asthma risk in observational studies, and available data suggest a causal association for some, none have been definitively shown to cause asthma directly. Avoidance or correction of these risk factors has not been shown to prevent asthma developing.

Observational studies have also identified various factors associated with reduced risk of developing asthma. However, deliberate exposure to these ‘protective’ factors has either not been investigated in high-quality studies, has not been shown to prevent asthma, or is inappropriate because known risks may outweigh theoretical benefit (e.g consumption of unpasteurised milk). These are routinely recommended for asthma prevention, with the exception of healthy eating patterns that have other known benefits, such as consumption of fish, polyunsaturated fatty acids, fruits, vegetables, and the Mediterranean diet.

Summary of key findings

Modifiable (or potentially modifiable) risk factors associated with childhood asthma include:4

  • prenatal exposure to tobacco smoke
  • maternal obesity during pregnancy
  • prenatal exposure to antibiotics
  • prenatal exposure to paracetamol
  • delivery by caesarean section
  • severe respiratory viral infections (e.g. with respiratory syncytial virus or rhinovirus) during infancy
  • exposure to moulds during infancy
  • exposure to outdoor air pollution during infancy
  • childhood overweight or obesity.

Modifiable risk factors associated with onset of asthma after early childhood include:

  • exposure to airborne sensitisers or irritants in the home (or in workplace for adult-onset work-related asthma)
  • exposure to a high concentration of rye grass pollen in the context of a thunderstorm.46

Major non-modifiable risk factors for asthma include atopy, genetics and prematurity.

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Heredity and genetics: effects on risk of developing asthma

Family history of asthma in one or more first-degree relatives is a risk factor for asthma.47

A child’s risk of developing asthma is increased if a parent has a history of asthma; approximately 3 times higher for mothers and 2.4 times higher for fathers.4

Several genes associated with increased risk of asthma have been identified.48 However, these genes explain very little of the inherited basis of asthma.

Asthma risk may be increased by the interaction between asthma susceptibility genes and environmental factors.49

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Smoking: effects on risk of developing asthma

Exposure to tobacco smoke toxins in utero or in infancy has been associated with increased risk of wheezing and asthma in children.4, 50

Maternal smoking during pregnancy is associated with an almost twofold increase in asthma in infants aged 2 years or less.50

Several large systematic reviews and meta-analyses of prospective cohort studies have reported that maternal smoking during pregnancy and exposure to tobacco smoke in infancy are associated with large increases in the risk of wheezing in the first 2 years of life.50, 51

A meta-analysis of observational studies (mainly cross-sectional studies) found that exposure to environmental tobacco smoke was associated with an increase in childhood asthma,52 but this association was weaker than that between exposure to environmental tobacco smoke and wheezing.

Epigenetic effects may modify the effects of environmental risk factors, including exposure to tobacco smoke, on development of asthma.53 However, a longitudinal cohort study54 found no association between smoking by grandparents (including during pregnancy with the mothers of the study cohort) early wheezing or asthma at age 7 in grandchildren.

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Paracetamol: effects on risk of developing asthma

Prenatal and childhood paracetamol use has been associated with increased asthma risk in several observational studies. However, causality has not been demonstrated. The effect is small, and the association may be due to confounding by indication.

Health professionals can advise pregnant women that there is some evidence from around the world that paracetamol use in pregnancy might increase the baby’s risk of wheezing or asthma, but that paracetamol is still considered the best option for pain relief in pregnant women.55

Prenatal exposure

Meta-analyses of observational studies (mainly prospective cohorts) show that paracetamol use during pregnancy is associated with increases in the risk of wheeze in early childhood and of childhood asthma at age 5 or older.4, 5, 6, 56, 8 However, this finding must be interpreted with caution because of heterogeneity among studies and the fact that some studies did not control for maternal respiratory tract infections.

Early life exposure

Several systematic reviews have reported an association between paracetamol use in infancy and development of asthma.57, 6, 8 However, many of the included studies were of low quality and the association may be due to confounding.

A meta-analysis of observational studies found that increasing frequency of use of paracetamol during infancy was associated with a small increase in the risk of childhood asthma, but the effect was reduced to very small after adjusting for respiratory tract infections.5 A recent systematic review of systematic reviews (overview)4 concluded that there was no significant association between paracetamol use during infancy and childhood asthma, after adjustment for lower respiratory tract infections.

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Bacterial environment: effects on risk of developing asthma

There is emerging evidence that asthma both influences, and is influenced by, the composition and function of the mixed-species communities of microbes that exist in the gut (intestinal microbiome) and respiratory tract (respiratory microbiome).58, 59

Mechanisms may involve the function of mucosal surfaces, epithelial barrier, local immunity, or a combination.60

The ‘hygiene’ hypothesis now understood as the ‘microbiome depletion’ or ‘microbiome deprivation’ hypothesis.61 Allergic asthma often has a genetic basis, but environmental and lifestyle factors are now understood to contribute to its development.

Gut microbiome

The composition of the gut microbiome matures within the first years of life.62 Early life microbial exposure appears to be important for early activation of the innate immune system and the development of regulatory immune responses, and may contribute to protection against asthma and allergy.60

Exposure to microbial diversity in the perinatal period is a potential protective factor for allergic asthma.63 The genera of bacteria that are considered to be determinants of a healthy mature gut composition include Faecalibacterium, Bifidobacterium, Roseburia, Alistipes, Flavonifractor, Lachnospiraceae incertae sedis, Ruminococcus and Dialister.62

A prospective longitudinal cohort study reported that 1-year-old children with an immature microbial composition had an increased risk of asthma at age 5 years.62 When stratified for maternal asthma status, this association was significant only among children born to mothers with asthma.62 This finding suggests that lacking microbial stimulation during the first year of life could trigger inherited asthma risk, while adequate maturation of the gut microbiome in this period might be protective.

The reported association between Caesarean section and increased risk of developing asthma, compared with vaginal delivery, appears to be due to altered intestinal bacterial flora.64, 65, 66

Exposure to antibiotics prenatally20, 67 (particularly during the second and third trimester),20 or in infancy,68, 69 is associated with a small increase in the risk of asthma. However, these associations may reflect confounding by indication57 and should be interpreted with caution.

Children’s exposure to some microorganisms (e.g. through living in farm environments70 or through maternal and infant consumption of unprocessed cow’s milk)65 has been repeatedly associated with reduced risk of asthma. Exposure to bacterial endotoxin and endotoxin load have also been associated with lower rates of asthma among school-aged children.71 This effect is thought to be due to changes in gene expression of innate immunity receptors in early life, promoting regulatory pathways that inhibit the allergic immune response.65, 72

  • Unpasteurised (raw) milk should not be consumed by children or adults because of the risk of harmful bacteria. The sale of raw milk for human consumption is illegal in Australia.

Lung microbiome

It is now recognised that the lower airways are populated by microbial populations, rather than being completely sterile as previously thought.73

The composition of the lung microbiome may affect immune response and lung function.74

The lower respiratory tract microbiome of people with asthma has been shown to differ from that of people without asthma.73 There is emerging evidence that the airway’s inflammatory status and its capacity for repair are associated with the composition of the airway microbiome, but the direction of cause and effect has not been established.74

Early microbial exposure and bacterial colonisation are important for developing a mature immune system, and is associated with the risk of allergies.58

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Breastfeeding and allergy prevention

Earlier evidence suggested that the risk of asthma might be reduced by prolonged exclusive breastfeeding. The reduction in risk was thought to be greatest in children at high risk of asthma, but small in other children.75 This evidence was mainly from studies of poor methodological quality.76

However, recent studies did not confirm that prolonged exclusive breastfeeding protected against development of asthma,77 allergic rhinitis,77 or other allergic disease such as atopic dermatitis (eczema).78 

Limited evidence from observational or poor quality studies suggests that breastfeeding while solid foods are introduced may help reduce the infant's risk of developing allergies.79 The Australasian Society of Clinical Immunology and Allergy (ASCIA) current guidelines for Infant feeding and allergy prevention recommend breastfeeding for at least 6 months for its range of benefits, with complementary foods introduced at around 6 months (but not before 4 months) while continuing to breastfeed.79

Exclusion of allergenic foods from the maternal diet has not been shown to prevent allergies.79 ASCIA recommends against maternal dietary restrictions while breastfeeding.79

ASCIA’s guidelines for Infant feeding and allergy prevention and Guide to introducing solid foods contain practical advice for mothers4 For updates on ASCIA advice, refer to the ASCIA website (www.allergy.org.au).

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Allergies and exposure to allergens: effects on risk of developing asthma

Note: Although allergic asthma is common, non-allergic asthma also occurs.

Population-based studies have observed a positive association between early life exposure to aeroallergens (house dust mite, mould)63 or sensitisation to aeroallergens80 and the development of asthma. However, exposure to allergens may not actually cause asthma.80

Allergic rhinitis is a major risk factor for asthma and often precedes it.81, 82, 83 These associations probably reflect the common allergic causes of both conditions, rather than a causal link.83

The combination of sensitisation to aeroallergens and viral infections early in life increases asthma risk.84

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Allergen avoidance in children: effects on risk of developing asthma

There is accumulating evidence from systematic reviews of intervention trials that single allergen reduction strategies, such as the use of mattress covers that are impermeable to house dust mite, are not effective in preventing the development of wheezing or asthma in children.85, 86

An Australian controlled clinical trial that compared house dust mite avoidance (acaricide and impermeable mattress covers), from birth to 5 years, with simple advice on cleaning, vacuuming, dusting and maintaining adequate ventilation,87, 88 reported no reduction in the risk of developing asthma at age 11.5 years.44

Multimodal allergen avoidance strategies that reduce exposure to both inhalant and food allergens, beginning in late pregnancy or from birth, may reduce the risk of asthma in children under 5 and in children over 5 years.86 However, these strategies require intensive effort and may not be feasible for many families.

Avoiding exposure to pets does not reduce asthma risk.89 There is even limited evidence that perinatal exposure to dogs or cats could reduce the risk of allergic disease.90

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Restriction diets during pregnancy and lactation: effects on children's risk of developing asthma

Systematic reviews of clinical trials of food allergen avoidance during pregnancy have found no overall reduction in rates of asthma or atopic dermatitis (eczema) in infants.24, 23 A 2012 Cochrane review concluded that prescription of antigen avoidance diets during pregnancy was unlikely to reduce substantially the risk of asthma or allergies in children with a family history of allergies.24

In contrast, two studies have since found that consumption of food allergens during pregnancy was associated with a lower risk of allergy and asthma in the offspring.91, 92

Restriction diets during pregnancy could also compromise maternal or foetal nutrition.24

The Australasian Society of Clinical Immunology and Allergy (ASCIA) allergy information for parents recommends against dietary restrictions during pregnancy or breastfeeding, and recommends that common food allergens (e.g. peanut, egg, fish, soy, cow's milk) should be fed to infants before age 12 months, starting at around 6 months (but not before 4 months).21

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Dietary supplementation during pregnancy and in newborns: effects on children's risk of developing asthma

Probiotics and prebiotics

Meta-analyses of clinical trials evaluating probiotics or prebiotics for the prevention of allergies in children have reported possible protection against atopic dermatitis (eczema),93 but do not show a reduction asthma.

Recent systematic reviews of clinical trials of probiotic supplementation during pregnancy or in early infancy reported that, overall, there was no statistically significant reduction in children’s rates of asthma or wheezing.26, 94, 28 Included trials varied in the type and duration of probiotic supplementation.

The Australasian Society of Clinical immunology and Allergy advises that ‘[w]hilst there is moderate evidence that probiotics during pregnancy and breastfeeding may help prevent eczema in early life, recommendations about probiotic supplements cannot currently be made because the optimal species and dose of probiotics that might have an effect is unclear.93

A systematic review and meta-analysis of clinical trials evaluating prebiotics (commonly oligosaccharides) added to infant feeds in the prevention of allergy found no significant effect on the rates of asthma development in children.25 It reported that there was some evidence that a prebiotic supplement added to infant feeds may prevent eczema, but that it was unclear whether the effects of prebiotic differed between children at high risk of allergy and the general population.25

Vitamin D

Meta-analysis of the two largest randomised clinical trials of vitamin D supplementation during pregnancy suggests that a daily dose of 4400 IU may reduce the risk of asthma/recurrent wheeze in the first 3 years of life, compared with the dose in standard multivitamin supplements (400 IU).32 The effect was greatest in those with a circulating 25-hydroxy-vitamin D concentration ≥ 30 ng/mL from study entry to delivery, suggesting that vitamin D levels in early pregnancy may be important.32

A systematic review of earlier randomised clinical trials reported a significant inverse association between the prenatal intake of vitamin D and children’s risk of developing recurrent wheeze.31 However, clinical trials have differed in doses and outcomes measured.

Vitamin D supplementation is routinely recommended for pregnant women:22

  • 1,000 IU (25 microg)/day for those with baseline blood levels 30–49 nmol/L
  • 2,000 IU (50 microg)/day for those with baseline blood levels < 30 nmol/L (with retesting at 28 weeks gestation)
  • 400 IU as part of a pregnancy multivitamin for women with baseline blood levels above 50 nmol/L.

Fish oil

A systematic review of prospective observational studies and RCTs found that asthma risk is reduced by high fish oil intake in children, including both fish consumption and long-chain omega-3 polyunsaturated fatty acids intake.95

However, recent systematic reviews of clinical trials evaluating prenatal long-chain omega-3 polyunsaturated fatty acid supplementation for allergy prevention found that supplementation had no effect on asthma or wheeze in children.38, 39 Earlier trials reported a reduction in asthma rates in children.40

Most studies were designed to measure other allergic outcomes (e.g. atopic dermatitis) and were not powered to detect effects on asthma risk.

The results of randomised clinical trials vary. A clinical trial comparing prenatal supplementation with fish oil (2.7 g of long-chain omega 3 polyunsaturated fatty acids) versus placebo (olive oil) or no intervention reported a significant reduction in the risk of asthma (measured as prescription of asthma medication) at up to age 18–19 years in the fish-oil group compared with the olive oil group, but no difference between groups in lung function or allergic sensitisation at age 18–19 years.96 In another randomised clinical trial, prenatal supplementation with 2.4 g fish oil per day was associated with a reduction in the rate of wheeze or asthma in children at 3-year follow-up.41 However, in a study in pregnant women with family history of allergic disease, supplementation with fish oil capsules (800 mg/d docosahexaenoic acid DHA and 100mg/d eicosapentaenoic acid) had no effect on asthma at 3 or 6 years’ follow-up, compared with placebo (vegetable oil capsules).42, 43

A systematic review of clinical trials evaluating infant supplements found that polyunsaturated fatty acids given as supplements or added to infant formula did not affect rates of asthma at up to age 2 years or at age 2–5 years.97

Australasian Society of Clinical Immunology and Allergy advises pregnant women that up to 3 serves of oily fish per week may be beneficial during pregnancy and breastfeeding, based on evidence for a protective effect of omega-3 fatty acids against atopic dermatitis in infants.

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Vitamins and nutrition: effects on risk of developing asthma

Overall, dietary intake of fruits and vegetables, and a range of vitamins, has been associated with lower rates of asthma or wheeze in systematic reviews of observational studies (mainly cross-sectional studies).98, 99, 100, 101

Higher diversity of food during the first year of life has also been associated with lower risk of developing asthma.65

Fruits and vegetables

Vegetable intake is inversely associated with risk of current asthma in adults and children.99 High vegetable consumption is associated with lower rate of wheeze and asthma in adults and children, compared with low vegetable consumption.100

High fruit consumption is associated with lower rate of wheeze and asthma in adults and children, compared with low fruit consumption.100

While the quality of evidence for a protective effect of fruits and vegetables is generally low, eating plenty of fruits and vegetables can be promoted for its general health benefits.

Fish oil

A systematic review of prospective observational studies and RCTs found that high fish oil intake (both fish consumption and long-chain omega-3 polyunsaturated fatty acids intake) was associated with reduced asthma risk reduced in children.95

Mediterranean diet

The ‘Mediterranean diet’ (high in fruits and vegetables, whole grains, oily fish and olive oil, and low in red meat) has been associated with lower rate of asthma or wheeze in systematic review of observational studies.98

Fast foods

High intake of fast foods by children has been associated with increased risk of developing asthma in observational studies.102, 103, 104, 105

Vitamin D

Pregnancy

There is epidemiological evidence for an association between low vitamin D in pregnancy and increased risk of wheeze and recurrent wheeze or asthma in early childhood106 and of developing asthma during the first 10 years of life.65 The quality of evidence varies, but the best available evidence from birth cohort studies reported an inverse association between maternal intake of vitamin D during pregnancy or cord blood level of vitamin D, and childhood wheeze.106 One systematic review reported a U-shaped relationship between maternal blood 25-hydroxyvitamin D levels and risk of childhood asthma, with the lowest risk at approximately 70 nmol/L.107

The results of clinical trials of vitamin D supplementation during pregnancy also suggest a protective effect against wheezing and asthma in early childhood.32, 31 However, clinical trials have differed in doses and outcomes measured. The findings of one trial suggest that vitamin D levels in early pregnancy may be important.32

Intake in childhood

Dietary intake of vitamin D in childhood is associated with lower rate of asthma or wheeze.98

Other vitamins

Dietary intake of vitamins C and E have been associated with lower rate of asthma or wheeze.98

Systematic review of observational studies shows that low maternal vitamin E intake during pregnancy is associated with increased risk of asthma in offspring up to age 10 years.65

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Low birth weight and prematurity: effects on risk of developing asthma

Preterm birth, low birth weight and related perinatal factors are associated with an increased risk of childhood asthma, according to meta-analyses of large datasets from observational studies, including many birth cohort studies.108, 109, 110, 111

Preterm birth (gestational age <37 weeks) and younger gestational age at birth are associated with higher risk of preschool wheezing and of asthma during childhood and adolescence.108, 110

Low birth weight (<2.5 kg) is associated with higher risk of wheezing disorders, asthma during childhood and adolescence, and asthma in adulthood.108, 109, 111 The related variable of weight gain velocity is also linked to asthma risk, with greater infant weight gain associated with risk of preschool wheezing and of asthma during childhood and adolescence.108, 110

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Caesarean section: effects on risk of developing asthma

Systematic reviews and meta-analyses of data from observational studies show an association between Caesarean section and a small increase in the child’s risk of developing asthma, compared with vaginal delivery.64, 65, 66

Some, but not all prospective birth cohort studies have reported an increase in asthma rates among children delivered by caesarean section.112, 113, 114, 115, 116, 117 Retrospective cohort studies and database studies,118, 119, 120, 121, 122, 123 case-control studies124, 125, 126 and population-based cross-sectional studies127, 128, 129 have reported inconsistent findings for follow-up of various intervals: some found an association between Caesarean section and asthma risk, while others did not.

The mechanism is thought to be due to effects of altered intestinal bacterial flora on the infant’s developing immune system.64, 65, 66

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Maternal and childhood obesity: effects on risk of developing asthma

Maternal obesity during pregnancy increases the risk of asthma or wheeze in children, based on a meta-analysis of observational studies.130

High gestational weight gain was also associated with higher risk of asthma or wheeze.130

Childhood overweight or obesity have also been associated with increased risk of developing asthma in some systematic reviews of observational studies.131, 132, 133

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Early life viral infections: effects on risk of developing asthma

Early life viral lower respiratory tract infections with respiratory syncytial virus (RSV) or rhinovirus are strongly associated with allergic asthma in childhood.134, 135, 136, 63

It is not yet known whether this association is due to inherited risk for both asthma and increased susceptibility to these viruses, or reflects alterations in immune response and lung function caused by the infection.134 Several genetic polymorphisms have been associated with wheeze following RSV lower respiratory tract infection in full-term infants.137

Estimates of attributable risk of asthma due to RSV are 13–22% among children aged 5 years and under, 11–27% among children aged 5–11 years, and 32% among children 12 years and over.138

The findings of one study suggested that prophylaxis with palivizumab (humanised IgG1 monoclonal antibody directed against RSV) in infants may reduce the risk of recurrent wheeze during the first year of life.139 However, longer-term follow-up found no effect on physician-diagnosed asthma or lung function at 6 years.140 At present, palivizumab use is mainly restricted to tertiary referral hospitals, where it is used to prevent severe RSV infection in susceptible infants (e.g. premature infants or those with congenital heart disease).

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Traffic air pollution: effects on risk of developing asthma

There is mounting evidence from observational studies for an association between pollution and asthma risk in children. However, it is difficult to control for the influence of confounding factors such as socioeconomic status.

In systematic reviews and meta-analyses:

  • prenatal exposure to air pollution (including nitrogen dioxide, particulate matter) was associated with increased risk of wheezing and asthma in children141
  • early life exposure to air pollution (nitrogen dioxide, ozone, volatile organic compounds, and particulate matter) was associated with increased risk of allergic asthma in children63
  • childhood exposure to traffic pollution including black carbon (soot from vehicle emissions), nitrogen dioxide, fine particulate matter, carbon monoxide and particulate matter, were associated with increased risk of asthma.142, 143

The role of traffic-related air pollution in the development of adult-onset asthma is less conclusive than in childhood asthma due to fewer studies and heterogeneity among studies.144

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Indoor air pollution: effects on risk of developing asthma

Epidemiological studies have consistently reported an association between early life exposure to indoor dampness and mould (particularly visible mould and mould odour)145 and increased risk of developing asthma or wheeze.145146147148 However, it is difficult to control for the influence of confounding factors such as socioeconomic status.

Exposure to fumes from polyvinyl chloride products (PVC) surface materials is associated with increased risk of asthma in children, while exposure to heated PVC fumes (mainly in the workplace) is associated with increased risk of asthma in adults.149

The use of gas stoves or ovens in the home has also been associated with development of asthma in children.150

Various indoor pollutants have also been associated with increased risk of adult-onset asthma. These include airborne substances used in the home (e.g. cleaning sprays)151 and many airborne substances encountered in workplaces.

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References

  1. Australasian Society of Clinical Immunology and Allergy,. Allergy prevention in children. ASCIA, 2009.
  2. Royal Australian and New Zealand College of Obstetricians and Gynaecologists,. Pre-pregnancy counselling. RANZCOG, 2017.
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  9. Koniman, R, Chan, Y H, Tan, T N, Van Bever, H P. A matched patient-sibling study on the usage of paracetamol and the subsequent development of allergy and asthma. Pediatr Allergy Immunol. 2007; 18: 128-134.
  10. Goksör, E, Thengilsdottir, H, Alm, B, et al. Prenatal paracetamol exposure and risk of wheeze at preschool age. Acta Paediatr. 2011; 100: 1567-1571.
  11. Bakkeheim E, Mowinckel P, Carlsen KH, et al. Paracetamol in early infancy: the risk of childhood allergy and asthma. Acta Paediatr. 2011; 100: 90-96. Available from: http://www.ncbi.nlm.nih.gov/pubmed/21143295
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