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Have you had your tonsils or appendix removed? If you have and you’re a woman, you probably weren’t told that the surgery may have increased your chances of having a baby.

In fact, you may have been told the opposite.

But a new 15-year study found that women who had their tonsils or appendix removed when they were young are more likely to get pregnant — and to do so earlier in life.

The reasons behind the link are not fully understood.

Researchers at the University of Dundee examined the medical records of more than 530,000 women across the United Kingdom and found pregnancy rates to be higher among women who had had their tonsils or appendix removed. Pregnancies were even higher among people missing both.

Rates of pregnancy among women without an appendix or tonsils were 54% and 53%, respectively, and rates in women lacking both parts of their body were 59%. This was higher than pregnancies among the group representing the rest of the population, which was almost 44%.

The findings go against previous theories in medicine that these surgeries, particularly appendectomies, reduce chances of fertility due to scar tissue forming around a woman’s fallopian tubes, where her eggs travel.

“The study has challenged the myth that was previously accepted on the deleterious effects of appendectomies,” said Dr. Sami Shimi, a consultant surgeon and clinical lecturer in surgery at the University of Dundee who led the study. “Young women should not have any fear or anxiety about an appendectomy (or tonsillectomy) reducing their fertility.”

The current research follows a report in 2012 that linked appendectomies to higher rates of pregnancy. The new study backs this previous insight on a wider scale but added the extra association with tonsillectomies and people who have undergone both surgeries.

Biology or behavior?

It’s hoped the findings will reassure women who need these surgeries, but the researchers are now eager to understand why fertility was seen to increase.

“We now need to find the mechanism,” Shimi said. He believes there could be either a biological or behavioral reason behind it. “We’re not discounting either for now.”

The biological contender is the idea that inflammation within the body from a continually inflamed appendix, or tonsils, puts strain and burden on the body, weakening it and potentially reducing chances of conception.

Alternatively, Shimi suggests that increased promiscuity among some women, and therefore increased contact and intimacy — through kissing or sex — may directly increase chances of tonsillitis or else chances of abdominal infection. The latter would not cause appendicitis as such but could lead to more abdominal infections or pain, which is more likely to lead to hospital referrals and investigations in which an inflamed appendix may be spotted more readily.

Both options need further investigation.

“It’s a very interesting association they’ve shown here,” said Richard Anderson, professor of clinical reproductive science at the University of Edinburgh, who wasn’t involved in the new study. “The issue is that it’s purely an association.”

Anderson warns that people may believe that the two factors — the surgeries and fertility — are causally linked, but “there’s no evidence of that here.” He added that the real question now is whether women who undergo these surgeries are more fertile or whether they are more likely to get pregnant at a younger age.

“Tonsillectomies are rare these days,” he added. “It’s whether women who chose to have their tonsils removed (rather than ongoing rounds of antibiotics) are also choosing to fall pregnant more often.”

Both Anderson and Shimi agree that the findings should instead be used to reassure women who need the surgeries and that those wanting to improve their fertility should not request to have them.

“Young women should not seek appendectomies or tonsillectomies to increase their chances of pregnancy,” Shimi said. “But if they need one, the operation will not reduce their future chances of pregnancy.”