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.

How this recommendation was developed

Adapted from existing guidance

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

  • Prescott and Tang, 20051

Advise pregnant women to use paracetamol when necessary, but to avoid unnecessary use.

How this recommendation was developed

Based on selected evidence

Based on a limited structured literature review or published systematic review, which identified the following relevant evidence:

  • Eyers et al. 20112

For pregnant women concerned about their child’s risk of developing asthma, do not recommend inhaled allergen avoidance during pregnancy as an effective way to prevent asthma.

How this recommendation was developed

Adapted from existing guidance

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

  • Prescott and Tang, 20051 

For pregnant women or parents of newborn infants concerned about their child’s risk of developing asthma, do not routinely recommend house dust mite avoidance during pregnancy as an effective way to reducing the child’s risk of developing prevent asthma.

How this recommendation was developed

Adapted from existing guidance

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

  • Prescott and Tang, 20051

For pregnant women concerned about their child’s risk of developing asthma, do not recommend dietary restrictions during pregnancy as an effective way to prevent asthma.

How this recommendation was developed

Based on selected evidence

Based on a limited structured literature review or published systematic review, which identified the following relevant evidence:

  • Kramer and Kakuma, 20063

If pregnant women with allergies or asthma are motivated to try allergen avoidance to reduce their baby’s asthma risk, advise that a comprehensive multi-allergen avoidance program, beginning during pregnancy or at birth, may reduce the risk of asthma in later childhood. This would involve low-allergen infant feed (breastfeeding by mother on a low-allergen diet, or partially hydrolysed [‘hypoallergenic’] formula) and house dust mite avoidance (as a minimum, acaricide and impermeable mattress covers).

Warn parents that multi-allergen avoidance strategies may be time-consuming and expensive, may not be feasible in Australia, and may not prevent the development of asthma in individual children.

How this recommendation was developed

Based on selected evidence

Based on a limited structured literature review or published systematic review, which identified the following relevant evidence:

  • Maas et al. 20094

For pregnant women concerned about their child’s risk of developing asthma, do not recommend probiotic dietary supplements during pregnancy as an effective way to prevent asthma.

How this recommendation was developed

Based on selected evidence

Based on a limited structured literature review or published systematic review, which identified the following relevant evidence:

  • Azad et al. 20135
  • Dotterud et al. 20106
  • Kalliomäki et al. 20077
  • Kopp et al. 20088
  • Kuitunen et al. 20099

For pregnant women concerned about their child’s risk of developing asthma, do not routinely recommend supplementation with vitamin A, D or E or fish oil during pregnancy as an effective way to prevent asthma.

How this recommendation was developed

Based on selected evidence

Based on a limited structured literature review or published systematic review, which identified the following relevant evidence:

  • Nurmatov et al. 201110
  • Paul et al. 201211
  • Prescott and Tang, 20051

More information

Factors reported to be associated with increased risk of developing asthma

Many factors have been associated with asthma risk in observational studies, but none have been shown to cause asthma directly. Avoidance or correction of these risk factors has not been shown to prevent asthma developing.

Allergies

A family history of allergy is associated with a high risk of allergic disease, including asthma.1

Several population-based studies have observed a positive association between sensitisation to aeroallergens (e.g. house dust mite and cat allergens) and the development of asthma (measured by various outcomes including wheeze, diagnosed asthma, or bronchial hyperresponsiveness), and other allergic diseases including atopic dermatitis (eczema) and rhinitis.12

Although sensitisation to allergens is associated with development of allergic asthma, it is unclear whether exposure to these allergens actually causes asthma.12 The combination of sensitisation to aeroallergens and viral infections early in life increases asthma risk.13

Epidemiological studies have consistently reported an association between exposure to indoor dampness and mould, and increased risk of developing asthma or wheeze.14, 151617

Rhinitis is a major risk factor for asthma and often precedes it.181920 Childhood allergic rhinitis increases the probability of asthma developing after childhood and the probability of having persisting asthma from childhood into middle age.19 These associations probably reflect the common allergic causes of both conditions, rather than a causal link. Non-allergic rhinitis is also a predictor of adult-onset asthma.20

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

Genetics

Several genes associated with increased risk of asthma have been identified.21 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.22

Other influences on immune system

Exposure to tobacco smoke toxins in utero or in infancy has been associated with increased risk of developing asthma.23

Observational studies have identified various factors associated with increased risk of developing asthma. However, avoidance of these ‘risk’ factors has not been shown to prevent asthma and is not recommended specifically as a strategy for prevention of asthma (regardless of any other potential health benefits). These factors include:

  • delivery by Caesarean section (possibly related to the fact that children born by Caesarean section have modified intestinal bacterial colonisation)24
  • the use of broad-spectrum antibiotics (macrolides or cephalosporins) in early childhood25 or pregnancy26
  • the use of paracetamol during pregnancy and infancy22728293031
  • some childhood infections (pertussis and measles)32
  • respiratory infections during the first two years of life.33343536,3738394041, 13 Early life viral infection in infants sensitised to aeroallergens is a strong risk factor for acute severe asthma-like symptoms and for developing asthma that persists into adulthood.13

Observational studies have identified various factors associated with reduced risk of developing asthma. However, deliberate exposure to these ‘protective’ factors has either not been investigated in good quality studies, or has not been shown to prevent asthma and is not routinely recommended for asthma prevention.  Identified factors include:

  • exposure to farm environments and contact with farm animals42
  • diets rich in oily fish43
  • some childhood viral and bacterial infections32
  • regular long-term low-dose aspirin use by adults.44
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Effects of prenatal and postnatal maternal smoking on asthma risk

Meta-analysis of data from cohort studies suggests that:

  • smoking during pregnancy increases the child’s risk of asthma before age 2 years by an estimated 85%23
  • in children aged 0–2 years, the risk of wheezing is increased by an estimated 70% if their mothers smoke.23

Although maternal smoking during pregnancy and exposure to cigarette smoke in early childhood significantly increase the risk of wheezing illness in early childhood, they probably do not increase the risk of allergic asthma later in life.4546

Data from a case-control study suggests that smoking during pregnancy not only increases the risk of asthma in children, but also the woman’s grandchildren.47

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Links between paracetamol and asthma risk

Prenatal exposure

Meta-analyses of data from prospective cohort studies and cross-sectional surveys have identified an association between prenatal exposure to paracetamol and increased risk of asthma and wheeze in children.227

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.48

Paracetamol use in children

Meta-analysis of cross-sectional population studies observed paracetamol use in previous year, and paracetamol use in first year of life, each associated with increased risk of asthma diagnosis in children aged 4–16 years.27

Some prospective cohort studies have reported an association between paracetamol use in infants,284929 children3050 or adolescents51 and increased risk of wheezing or asthma. However, an Australian study observed no association between paracetamol use and asthma risk after adjusting for frequency of respiratory infections.31

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Inhaled allergen avoidance during pregnancy

The current position statement on the prevention of allergy in children by the Australasian Society of Clinical Immunology and Allergy (ASCIA) does not recommend pregnant women should attempt to avoid inhaled allergens.1 For updates on ASCIA advice, refer to the ASCIA website (www.allergy.org.au).

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Dietary restriction during pregnancy for allergy prevention

Avoidance of commonly allergenic foods during pregnancy or lactation has not been shown to reduce the risk of developing asthma during childhood, and may even increase the risks of preterm birth and lower birth weight.3

Although a combination of maternal hypoallergenic diet during pregnancy and dust mite allergen avoidance strategies (acaricide sprays and mite-impermeable mattress covers) was reported in one study52 to reduce the risk of asthma in children, overall evidence does not support generally recommending this strategy. Hypoallergenic diets for pregnant women may result in inadequate nutrition, and are not recommended (except when advised by a specialist allergist and supervised by an accredited practising dietitian).

The current position statement on the prevention of allergy in children by the Australasian Society of Clinical Immunology and Allergy (ASCIA) does not recommend dietary restrictions during pregnancy.1

For updates on ASCIA advice, refer to the ASCIA website (www.allergy.org.au).

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Dietary supplementation during pregnancy and in newborns

Folic acid

Observational studies have reported conflicting findings on the association between folic acid supplementation during pregnancy and asthma.53 Various studies have reported either that folic acid supplementation late in pregnancy (but not early) was associated with increased risk of childhood asthma, that folic acid supplementation early in pregnancy (but not late) was associated with increased risk of childhood wheeze, or no association between folic acid supplementation and infant wheeze.53

Probiotics

Probiotic or prebiotic supplementation of mothers during late pregnancy and lactation, or of non-breastfed infants, does not appear to prevent asthma,569875455 although infant feeding with prebiotics may reduce atopic dermatitis (eczema) risk.55

Vitamins

A meta-analysis of observational cohort studies observed that high maternal dietary vitamin D and E intakes during pregnancy were associated with reduced risk of wheezing.10 However, there is insufficient evidence from intervention studies demonstrating protective effects of vitamins to recommend supplementation.1011

Fish oil

Fish oil has a range of anti-inflammatory properties.56

Overall, evidence from studies assessing the effectiveness of fish oil supplementation in preventing allergy suggest that protective effects are probably greatest in pregnancy (i.e. earlier in development).56 Epidemiological studies suggest that dietary fish oil in pregnancy and early childhood may protect against asthma and allergic disease.5657 However, there is insufficient evidence from randomised controlled intervention studies to determine whether supplementation during pregnancy should be recommended to reduce asthma risk in children.

Studies in which fish oil supplementation was commenced in early childhood have not shown reductions in asthma risk.56, 58

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Allergen avoidance in children

Exposure to pets

Pooled analysis of a large set of data from 11 European birth cohorts suggests that living with a furry or feathered pet during infancy neither increases nor decreases the risk of asthma or allergic rhinitis at ages 6–10 years, compared with no exposure to pets.59

House dust mite avoidance in newborns

House dust mite avoidance measures alone are unlikely to prevent a child developing wheezing or asthma, based on the findings of randomised controlled trials in prenatally recruited infants at risk of allergies and asthma due to family history or demonstrated sensitisation,606162, 646563, 66676869 including an Australian study that compared house dust mite avoidance (acaricide and impermeable mattress covers) with simple advice on cleaning, vacuuming, dusting and maintaining adequate ventilation and followed children from 18 months to 11 years.64656370

In one randomised controlled trial of prenatally recruited infants at high risk of allergies and asthma (both parents atopic), prenatal and postnatal house dust mite avoidance (mite-impermeable mattress, pillow and quilt covers, HEPA filter vacuum cleaner, replacement of carpet with vinyl flooring, custom cot and basinet mattresses, washable soft toy, hot washing of bed linen, acaricide) was associated with reduced rates of wheezing during the first year of life compared with usual care,68 but respiratory symptoms at age 3 years did not differ between intervention and control groups.69

Multi-allergen avoidance in newborns

While interventions involving a single strategy have not been successful in reducing asthma risk, multifaceted interventions that involve dietary allergen reduction and environmental allergen avoidance from birth or prenatally may reduce asthma risk.4 A systematic review and meta-analysis of randomised controlled trials assessing allergen avoidance commenced prenatally or at birth found that reduction of exposure to multiple allergens reduces the likelihood of a current diagnosis of asthma in children (at ages younger than 5 years, and 5 years and older), compared with usual care.4 The risk of doctor-diagnosed asthma at age 5 and over was approximately halved.

In a randomised controlled clinical trial that compared the combination of hypoallergenic infant diet (extensively hydrolysed formula or breastfeeding with mothers on low-allergen diet) and house dust mite avoidance strategies (acaricide and impermeable mattress covers) with standard advice,527172737475  the intervention group showed lower rates of asthma at ages 1 year,7375 8 years,72 and 18 years,71 but no difference between intervention and control group in asthma rates at 2 years7374 and 4 years.73 The reduction in asthma prevalence at 18 years and overall prevalence was mainly due to a reduced rate of asthma that developed in childhood and persisted to 18 years.71

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References

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  2. Eyers S, Weatherall M, Jefferies S, Beasley R. Paracetamol in pregnancy and the risk of wheezing in offspring: a systematic review and meta-analysis. Clin Exp Allergy. 2011; 41: 482-9. Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2222.2010.03691.x/full
  3. Kramer MS, Kakuma R. Maternal dietary antigen avoidance during pregnancy or lactation, or both, for preventing or treating atopic disease in the child. Cochrane Database Syst Rev. 2006; Issue 3: CD000133. Available from: http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD000133.pub2/full
  4. Maas T, Kaper J, Sheikh A, et al. Mono and multifaceted inhalant and/or food allergen reduction interventions for preventing asthma in children at high risk of developing asthma. Cochrane Database Syst Rev. 2009; Issue 3: CD006480. Available from: http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD006480.pub2/full
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