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Women who have their babies by caesarean section (CS) are given antibiotics to prevent infection of the wound. In the past, these antibiotics were given to the mother after the cord was clamped so none of the antibiotics passed to the baby. Since 2011, national guidelines have recommended that antibiotics are given to the mother before the skin is cut for the CS, as there is good evidence that this reduces the risk of wound infection.
A possible disadvantage of giving the antibiotics earlier is that babies born by CS will get a dose of antibiotics just before birth. Having antibiotics early in life may affect the balance of ‘good bacteria’ and other organisms in the gut (the gut microbiome). This, in turn, might increase the chance that the babies will develop allergic diseases such as eczema, hay fever and asthma when they are older. There are likely to be many different causes of asthma and allergic disease; antibiotics are just one possible part of the puzzle. We do not yet know if antibiotics in early life will increase or decrease the risk of developing allergic diseases (although current knowledge suggests that if there is any effect, it will involve an increased risk).
The Born in Bradford (BiB) birth cohort study, which includes over 10,000 children in total, provides the opportunity of a natural experiment to compare the risk of allergic disease in children born by CS and exposed to antibiotics with those born by CS but not exposed to antibiotics. The cohort includes babies born between 2007 and 2011 and a review of maternity notes indicates a change in the timing of giving antibiotics around 2009/2010 in Bradford. This means that pre-incision antibiotics were given ‘routinely’ in some CS births but not others, rather than for any reason linked to the risk of infection in the mother or baby. The findings of previous studies on the association between antibiotics and asthma have been difficult to interpret because the symptoms or infections for which the antibiotics are given to children might be related to asthma or risk factors for asthma.
Information on timing of birth and antibiotics will be collected from the maternity notes for each BiB child born by CS (n=2443) to determine whether or not they were exposed to antibiotics just before birth. We have already collected data on atopic status (a positive reaction to at least one allergen on skin prick testing indicating an increased risk of allergic disease) at age 4 years (for a total of 2269 children) and questionnaire data on parental report of eczema or hay fever at age 2 years (n=2052) and eczema, hay fever, wheeze or asthma at age 4 years (n=2594). In addition, we have linked data on GP diagnoses and prescriptions for allergic disease for all BiB children (n=10,915). Detailed information on other factors which might affect the relationship between antibiotic exposure and allergic disease, such as breastfeeding and pet ownership, has been collected from BiB children. We will also be able to account for antibiotic exposure at other times (earlier in utero if mother treated with antibiotics during pregnancy; during infancy/childhood) using linked primary care data.
The findings of this study will show whether having antibiotics at birth increases the risk of children subsequently developing hay fever, eczema or asthma. The findings will help us decide the best time to give antibiotics to women during CS, by balancing the benefits and risks to the mother and her child.