Student guest post by Shylo Wardyn
I recently read the book ‘Good Germs, Bad Germs’ by Jessica Snyder Sachs. I became intrigued by parts of her book that discussed how babies become colonized with bacteria during birth. The most interesting part was the differences between vaginally-delivered and Caesarean-delivered babies. It was not something I had ever thought of before. With my interest piqued, I did a Google scholar search to see what kind of research was being done on this topic. I stumbled upon an article looking at C-sections and risk of childhood allergies, namely asthma. I realized this would be the perfect topic for this assignment!
A little background information:
Asthma is a chronic inflammatory disorder of the airways that affects both children and adults. It is not known why some people develop asthma and others don’t. Rates of asthma have more than doubled from 1980 to 2004 in children <18, but since 2001 have held steady. It is noteworthy to mention that the definition of asthma was altered in 2001, as well (Moorman, et al., 2007). A Caesarean section (C-section) is a surgical procedure in which an incision is made through the mother's abdomen and uterus to deliver one or more babies. While C-sections are traditionally done when a vaginal delivery poses risk to the mother or baby, women can also elect to have a C-section instead of a normal delivery. C-section delivery rates account for 31.8% of all births in the United States; 2007 marked the 11th consecutive year of increase and a record high for the US (Hamilton B.E., 2009). The neonatal period is critical for bacterial colonization of the intestines. Infants delivered vaginally acquire their intestinal flora from their mother's vaginal and fecal flora, generally species of Bacteroides, Lactobaccilus and Bifidobacteria. This intestinal flora colonization is delayed in Caesarean delivered infants; consequently, their gut flora is abnormal for weeks to months. One study found that in Caesarean delivered infants at the age of 6 months, the colonization rate of Bacteroides was half that of infants in the vaginally delivered group (Grölund, 1999). The research: Gut normal flora has a significant impact on the immune system; normal flora strains have been shown to induce the production of IL-10, which has an important regulatory role in the development of the allergic immune response (Kalliomaki & Isolauri, 2003). This is the biological hypothesis behind the proposed association between C-sections and asthma. This issue has been studied, but results are conflicting. I found two meta-analyses that looked at the research to date. Thavagnanam (S. Thavagnanam, 2007) found a 20% increase in the risk of asthma in children who had been delivered by Caesarean. While Bager et al. also found a moderate increase in the risk of asthma after Caesarean, they did not attribute this to the increasing rates of C-sections (Bager, Wohlfahrt, & Westergaard, 2008). They felt that for this to be the case, C-section deliveries should be associated with all allergic outcomes, not just some of them. I felt that they discredited their study by stating this; they still found a biologically plausible and significant association between C-section delivery and asthma. A more recent Norwegian population-based cohort study confirmed a moderate association between C-section and asthma (Tollanes, Moster, Daltveit, & Irgens, 2008). Probiotics and general remarks: While there clearly needs to be more research about the exact role of gut flora in the development of allergies, an interesting area of research is in probiotics. Probiotics are cultures of beneficial bacteria of the normal gut flora. Studies have shown that probiotics administered to pregnant women and their newborns lead to lower rates of development of allergic diseases (including asthma). However, these studies looked at high-risk children; those that had a first degree relative or parent with any allergic disease (Kalliomaki, et al., 2001; Kuitunen, et al., 2009). I couldn't find any randomized placebo-controlled trials with babies delivered by C-section as the group of interest. I think that would be a great study and would answer a lot of questions. While it seems this is still a new area of research, I think the studies speak for themselves. If this information was more widely disseminated, maybe some women would think twice before electing to have a C-section. Maybe in the future, parents will be advised to give their newborns that were delivered by C-section probiotics. Or maybe everyone will be prescribed probiotics after taking broad-spectrum antibiotics....but that is for another blog! Bager, P., Wohlfahrt, J., & Westergaard, T. (2008). Caesarean delivery and risk of atopy and allergic disease: meta-analyses. Clin Exp Allergy, 38(4), 634-642. Grölund, M.-M. L., Olli-Pekka; Eerola, Erkki; Kero, Pentti. (1999). Fecal Microflora in Healthy Infants Born by Different Methods of Delivery: Permanent Changes in Intestinal Flora After Cesarean Delivery. Journal of Pediatric Gastroenterology & Nutrition, 28(1), 19-25. Hamilton B.E., J. A. M., S.J. Ventura. (2009). Births: Preliminary Data for 2007. Kalliomaki, M., & Isolauri, E. (2003). Role of intestinal flora in the development of allergy. Curr Opin Allergy Clin Immunol, 3(1), 15-20. Kalliomaki, M., Salminen, S., Arvilommi, H., Kero, P., Koskinen, P., & Isolauri, E. (2001). Probiotics in primary prevention of atopic disease: a randomised placebo-controlled trial. Lancet, 357(9262), 1076-1079. Kuitunen, M., Kukkonen, K., Juntunen-Backman, K., Korpela, R., Poussa, T., Tuure, T., et al. (2009). Probiotics prevent IgE-associated allergy until age 5 years in cesarean-delivered children but not in the total cohort. J Allergy Clin Immunol, 123(2), 335-341. Moorman, J. E., Rudd, R. A., Johnson, C. A., King, M., Minor, P., Bailey, C., et al. (2007). National surveillance for asthma--United States, 1980-2004. MMWR Surveill Summ, 56(8), 1-54. S. Thavagnanam, J. F., A. Bromleyz, M. D. Shields and C. R. Cardwell. (2007). A meta-analysis of the association between Caesarean section and childhood asthma. Clinical and Experimental Allergy, 38, 629-633. Tollanes, M. C., Moster, D., Daltveit, A. K., & Irgens, L. M. (2008). Cesarean section and risk of severe childhood asthma: a population-based cohort study. J Pediatr, 153(1), 112-116.