Women without an appendix or tonsils are more fertile

Women who have had their appendix or tonsils removed appear more likely to become pregnant and do so sooner, according to a study.

The reasons for the association are not yet understood, and doctors had previously believed that removing the appendix could be detrimental to fertility.

'For many years medical students were taught that appendectomy had a negative effect on fertility, and young women often feared that having their appendix removed threatened their chances of later becoming pregnant,' said Sami Shimi, clinical senior lecturer at the University of Dundee Medical School, who was lead researcher for the study. 'This scientifically challenges the myth of the effect of appendectomy on fertility. What we have to establish now is exactly why that is the case.'

The study, published in Fertility and Sterility, analysed the medical records of more than half a million women over 25 years. Pregnancy rates were significantly higher among those who had had an appendectomy (54.4 percent), tonsillectomy (53.4 percent) or both (59.7 percent) than among those who had had neither (43.7 percent).

In a 2012 study the same team had reported an association between appendectomy and increased fertility. The researchers had suggested at that time that this might be due to the negative impact of pelvic inflammation, caused by the appendix, on reproductive organs. However, the additional association between tonsillectomy and increased fertility suggests that the explanation may be related to other immunological or behavioural factors.

'There are several explanations which may account for these observations, one of which is that the removal of these tissues makes an alteration to their immune system which has an impact to some aspect of the reproductive process, such as how their embryos implant in the womb,' Professor Allan Pacey of the University of Sheffield, who was not involved in the study, told BBC News. 'If so, this may ultimately give doctors and scientists some new ideas for novel drugs or therapies to enhance women's fertility.'

Dr Li Wei of University College London, the study's co-author, offers a different potential explanation: 'Although a biological cause is possible, we believe that the cause is more likely to be behavioural. We are pursuing both hypotheses with further research.' For example, women who have more sexual partners are more likely to have pelvic inflammatory disease, which could lead to them having their appendix removed.

The authors emphasised that this is a cohort study and only demonstrates association, not causation. There is no reason to think that removal of the appendix or tonsils would improve fertility, they cautioned.