The latest study to report a link between being born by cesarean delivery and developing asthma has been reported in Norway this month by Tollanes et al. The researchers' discovery that "children delivered by CS had a 52% increased risk of asthma compared with spontaneously vaginally delivered children" made for many negative news headlines. However, it's important to note - in the context of healthy women who choose a planned cesarean delivery at 39 weeks gestation - that Tollanes et al's conclusion actually cites "a moderately increased risk of asthma in the children delivered by CS [and further, that the] possibly stronger association with emergency CS compared with planned CS could be worth pursuing to investigate possible causal mechanisms."
The fact is, it is currently impossible to say for sure whether a link categorically exists between asthma and cesarean delivery, and indeed other research carried out has pointed to other causal factors (see below) as opposed to the mode of delivery itself. As always, if cesarean statistics were separated, the job of researchers would be made a whole lot easier, measurements would be more precise, and as a consequence, women would be provided with a much clearer picture of risk.
The fact is, it is currently impossible to say for sure whether a link categorically exists between asthma and cesarean delivery, and indeed other research carried out has pointed to other causal factors (see below) as opposed to the mode of delivery itself. As always, if cesarean statistics were separated, the job of researchers would be made a whole lot easier, measurements would be more precise, and as a consequence, women would be provided with a much clearer picture of risk.
In the meantime, if you are concerned about the risk of asthma for your child, you might be interested in reading some of the research links and media reports listed below:
RELATED RESEARCH
*2008 A meta-analysis of the association between Caesarean section and childhood asthma, Thavagnanam et al
Conclusion: In this meta-analysis, we found a 20% increase in the subsequent risk of asthma in children who had been delivered by caesarean section.
*2008 Continued Exposure to Maternal Distress in Early Life Is Associated with an Increased Risk of Childhood Asthma, Kozyrskyj et al
Conclusions: Maternal distress in early life plays a role in the development of childhood asthma, especially if it continues beyond the postpartum period.
*2006 Mode of delivery is associated with asthma and allergy occurrences in children, Salam et al
Children born by c-section were at increased risk for asthma, hay fever, and allergy compared with those born vaginally. Risk associated with c-section was the same for children regardless of family history of asthma or allergy. Conclusion: We conclude that birth by c-section or processes associated with it may increase the risk for atopic disease in childhood.
*2005 Mode of delivery at birth and development of asthma: a population-based cohort study, Juhn et al
Conclusion: Mode of delivery is not associated with subsequent risk of developing childhood asthma or wheezing episodes. Because the effect of mode of delivery on a risk of developing asthma or wheezing episodes varies over time (ie, age), selection of the study subjects according to their ages may have influenced the findings of previous studies with a shorter follow-up period.
*2005 Perinatal characteristics and obstetric complications as risk factors for asthma, allergy and eczema at the age of 6 years, Bernsen et al
Conclusions: Prematurity is a risk factor for asthma reported at 6 years. A high ratio of head circumference to birth weight is a risk factor for any atopic disorder. Vacuum extraction was associated with a higher risk of allergy, and induced labour is a risk factor for inhalant allergy. All results should be viewed with the possibility of residual confounding.
*2005 Caesarean section delivery and the risk of allergic disorders in childhood, Renz-Polster et al
Conclusion: Caesarean sections may be associated with an increased risk of developing AR [allergic rhinoconjunctivitis] in childhood.
*2005 Childhood asthma hospitalization risk after cesarean delivery in former term and premature infants, Debley et al
Conclusions: Cesarean delivery was associated with subsequent asthma hospitalization only in premature infants. Because mothers with asthma are reported to have increased rates of cesarean delivery and premature delivery, other factors in addition to the hygiene hypothesis, including genetic and in utero influences associated with maternal asthma, may contribute to the increased risk of asthma in premature infants.
*2005 Childhood asthma hospitalization risk after cesarean delivery in former term and premature infants, Debley et al
Cesarean delivery was associated with subsequent asthma hospitalization only in premature infants. Because mothers with asthma are reported to have increased rates of cesarean delivery and premature delivery, other factors in addition to the hygiene hypothesis, including genetic and in utero influences associated with maternal asthma, may contribute to the increased risk of asthma in premature infants.
*2004 Mode of delivery is not associated with asthma or atopy in childhood, Maitra et al
Conclusion: Delivery by caesarean section was not associated with the subsequent development of asthma, wheezing or atopy in later childhood in this population.
*2003 Mode of delivery and risk of allergic rhinitis and asthma, Bager et al
Conclusions: Our findings do not support the hypothesis that cesarean section or other complicated modes of delivery are associated with the development of allergic rhinitis. However, there might be a positive association with development of asthma - in particular, for cesarean section - that was not explained by gestational age, birth weight, ponderal index, smallness for gestational age, parity, maternal age, or occupation.
*2003 Caesarean section increases the risk of hospital care in childhood for asthma and gastroenteritis, Håkansson et Källén
Conclusion: There is a significant increase of the risk for developing symptoms of asthma and/or gastroenteritis that motivates admission for hospital care in cesarean children older than 1 year. It is speculated that a disturbed intestinal colonization pattern in cesarean children may be a common pathogenic factor.
*2002 Mode of delivery and asthma -- is there a connection? Kero et al
The register study showed the cumulative incidence of asthma at the age of seven to be significantly higher in children born by caesarean section (4.2%) than in those vaginally delivered (3.3%)... In the second study, significantly more positive allergy tests were reported in questionnaires in the caesarean (22%) than in the vaginal delivery group (11%), and a trend toward more positive skin prick reactions was documented at clinical examination; 41% versus 29%. In conclusion, these results suggest that caesarean section delivery may be associated with an increased prevalence of atopic asthma.
*2001 Caesarean section and risk of asthma and allergy in adulthood, Xu et al
Prospective birth cohort born in northern Finland in 1966: Cesarean had a strong effect on current doctor-diagnosed asthma in adulthood [in 1997, aged 31]... However, no substantial effects were observed for atopy, hay fever, and atopic eczema.
*2001 Gaps in Primal Research, Odent M
...looked at the incidence of asthma in 1,953 people aged 31 who were born in 1966. Those born by caesarean were 3 times more at risk of being diagnosed with asthma but the study did not separate emergency from planned operations [and] one can assume that in 1966 most caesareans were born during labour.
*1998 Infant and maternal outcomes in the pregnancies of asthmatic women, Demissie et al
After controlling for the effects of important confounding variables, maternal asthma was associated with the following adverse infant outcomes: preterm infant, low birth weight, small-for-gestational age, congenital anomalies, and increased infant hospital length of stay. The adverse maternal outcomes associated with maternal asthma were: pre-eclampsia, placenta previa, cesarean delivery, and increased maternal hospital length of stay. The results emphasize the need for maternal asthma to be added to the list of conditions that increase the risk of adverse pregnancy outcomes.
PREVIOUS NEWS REPORTS
*15 Jul 08 Asthma risk from pregnancy nuts, BBC news online
*04 Mar 07 Damp homes 'could cause asthma', BBC news online
*20 Nov 06 Milk allergy in babies 'missed', BBC news online
*11 Nov 06 Diet may help prevent allergies and asthma, Scientist Live
*09 Sep 06 Food allergies 'gone in 10 years', BBC news online
*25 Aug 06 Childhood allergies 'more widespread', Guardian (PA)
*07 Dec 01 Vitamin link to asthma, BBC news online
*15 Nov 01 Firstborn 'more prone to allergies', BBC news online
*27 May 01 Keeping pets 'prevents allergies', BBC news online
*06 Mar 01 Allergy hope for asthmatic children, BBC news online
*12 May 00 Dust 'protects against asthma', BBC news online
*09 May 00 Your bedding could make you ill, BBC news online
*11 Feb 00 Dirt could be good for you, BBC news online
*17 Dec 99 Allergy warning over processed food, BBC news online
*08 Jun 99 Childhood asthma soars, BBC news online
*05 Feb 99 Nursery may protect against allergies, BBC news online
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