More on the Hygiene Hypothesis and Exposure to Coliform Organisms from the Birth Canal

The putative advantages of a deep draught of coliform organisms during a baby’s journey into the world has been discussed in a previous News Blog, with respect to prevention of allergy.[1] It now seems that it is not just allergy, but also cancer – more specifically the acute leukaemia of childhood – that is influenced by the process of birth.[2] And again, bypassing the birth canal by means of Caesarean section increases risk. The mechanism seems to conform with the three hits hypothesis, described in a past News Blog.[3] Here the hits might be:

  1. Genetic predisposition.
  2. Failure to ‘benefit’ from exposure to coliforms during birth.
  3. Subsequent severe infection.

Regarding the third ‘hit’ above, it is known that acute lymphoblastic leukaemia of children occurs in semi-epidemic fashion, suggesting that an acute infection is the trigger.

Some decades ago I carried out a decision-analysis that argued that when the risk of intra-partum C-section exceeded a threshold of around 35%, then a planned C-section was the best option for mother and baby.[4] For the mother because intra-partum C-section is more risky than planned C-section; and for the baby because situations where intra-partum C-section is common usually imply that the baby is also at increased risk – for example if the baby is coming by the breach. However, I can now see that my decision-analysis was incomplete – maybe I should have factored in the ‘unknown unknowns’.

— Richard Lilford, CLAHRC WM Director


  1. Lilford RJ. Exposure of the Baby to a Rich Mixture of Coliform Organisms from the Birth Canal. NIHR CLAHRC West Midlands News Blog. 22 April 2016.
  2. Greaves M. A causal mechanisms for childhood acute lymphoblastic leukaemia. Nat Rev Cancer. 2018.
  3. Lilford RJ. Three Hits Hypothesis. NIHR CLAHRC West Midlands News Blog. 7 April 2017.
  4. Lilford RJ, van Coeverden de Groot HA, Moore PJ, Bingham P. The relative risks of caesarean section (intrapartum and elective) and vaginal delivery: a detailed analysis to exclude the effects of medical disorders and other acute pre-existing physiological disturbances. Br J Obstet Gynaecol. 1990; 97(10): 883-92.

One thought on “More on the Hygiene Hypothesis and Exposure to Coliform Organisms from the Birth Canal”

  1. Richard, I commend you for realising your previous decision analysis was incomplete – but are you going to repeat it, factoring in the new knowns and the unknown unknowns [that might come from millions of years of evolution/ complexity – ie the idea that (albeit with pathologies) labour is an ontological and ‘enlivening’ process]? You, and many other obstetricians had a powerful impact on views on elective section that need revision

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