A surprising link has been found between women who have had their appendix and/or tonsils removed and their rate of fertility, although doctors are strongly warning against any women considering either procedure unnecessarily. The researchers think that the factors behind the results, which are published in the journal Fertility and Sterility, could be more behavioral than biological.

While correlation does not necessarily equal causation, the researchers think certain factors could be affecting the rate of fertility, as this isn’t the first time that such a link has been discovered between the appendix and fertility. Two previous studies in the UK have found that women who have undergone an appendectomy have an increased fertility rate – of 20 and 54 percent, respectively – and shorter time to pregnancy, as well as another Swedish study finding a similar association.

One reasoning might be whether a patient is susceptible to repeat infections of the appendix. By removing the organ completely, it may prevent any infection or swelling that could then cause damage to the fallopian tubes, and in turn impact a woman’s fertility. In order to test this, the researchers decided to look at another lymphoid organ – this time the tonsils. If the cause for the increase in fertility has to do with a reduction in swelling around the fallopian tubes, then it would stand to reason that the removal of the tonsils would have no effect, or so they thought.

What they found was even more curious. They looked at over 500,000 women who had either just undergone an appendectomy, just had a tonsillectomy, both, or neither, and matched them for exact age and practice over 15 years. They found that out of each group, 54 percent of the 54,675 who had had their appendix removed went on to become pregnant, as did 53 percent of the 112,607 tonsillectomy patients, and close to 60 percent of those 10,340 who had both taken out. This was compared to just 43 percent of the 355,244 women who had neither procedure. Not only that, but they also showed shorter time to pregnancy.

“The results from this population-based study confirmed the previously reported observation of a higher pregnancy rate and shorter [time to pregnancy] after appendectomy,” write the authors, “[but] we were further surprised to find that removal of the tonsils also increased the subsequent pregnancy rate.” The reasons behind this apparent increase in fertility and shortened time to pregnancy might not be so much biological, however, as behavioral.

The researchers write that by selecting for patients who had had either their appendix, tonsils, or both removed, they may have been inadvertently selecting for women who also had a “more liberal attitude towards sex”, and thus were more likely to get pregnant. They note that the women in these groups in the study had “a higher rate of chlamydial infections, pelvic inflammatory disease, and previous pregnancies, all of which are surrogate markers for increased sexual activity.”

However, the researchers say that they cannot rule out the fact that by removing these lymphatic organs, it could reduce the amount of inflammation within the body as a whole. This, they argue, could aid in the implantation of an egg into the uterus. They point to other conditions of increased inflammation, such as asthma, and the reduced fertility and longer time to pregnancy seen in those patients.

So, it seems that there could be a mix of factors involved here, both biological and behavioral, but one thing is for certain: No one should have either their appendix or tonsils removed unless it is absolutely necessary.