Putting to Rest Fears that IVF May Be Linked to Cancer

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In the wake of Elizabeth Edwards’ death, many women are wondering whether the fertility treatments the former Senator’s wife underwent to bear children late in life — she leaves behind two young children, ages 10 and 12 — could have contributed to the breast cancer that killed her.

It’s a plausible concern, given that fertility treatment exposes women to unnaturally high levels of hormones, including estrogen and progesterone — often repeatedly, and sometimes at an age when those hormones would normally be declining. Previous data have suggested that these fertility drugs may be associated with increased risk for breast, uterine and ovarian cancers. (More on Time.com: Building a Brighter Kid: Consider IVF)

But a large new study published this month in Human Reproduction suggests that women who undergo in-vitro fertilization (IVF) — the procedure Edwards used to conceive her youngest children — do not put themselves at a higher-than-usual risk of cancer. The study examined data on all IVF births in Sweden between 1982 and 2006, comparing the rate of cancer in 24,058 women who conceived via IVF with that of nearly 1.4 million Swedish mothers who did not require fertility treatment.

The study found that the risk for any cancer was actually 26% lower in women after they had children through IVF, compared with those who had conceived the old-fashioned way. Breast cancer risk was reduced 24% and cervical cancer risk 39%, over the eight-year follow-up period. (More on Time.com: Photos: The Landscape of Cancer Treatment)

“The ultimate message is that there is no increase in cancer risk associated with IVF,” says Dr. Don Dizon, associate professor of obstetrics-gynecology at the Alpert Medical School of Brown University, who was not associated with the research.

However, women who underwent IVF started out with higher rates of cancer than those in the general population; the fact that these women were more likely to have been treated for cancer, which causes infertility, is probably why they sought IVF. This risk was especially elevated for ovarian cancer: in women seeking IVF the risk of ovarian cancer was nearly four times greater than in other mothers before conception. That is likely because the same problems that contribute to ovarian cancer may also produce infertility. “If you have an ovary that has a tendency to develop into cancer, it might also be poorly functioning reproductively,” says Dr. Bengt Kallen, professor emeritus at the University of Lund and lead author of the study. (More on Time.com: Special Report: Advances for Breast Cancer Patients)

However, the study found that the risk of ovarian cancer in women who were able to conceive and give birth to a baby through IVF was only twice as high as in mothers who conceived naturally. The effect was not because IVF reduces the odds of developing ovarian cancer, the authors say; instead, it’s more likely that women who are able to conceive and successfully carry a pregnancy by IVF are probably healthier than other women, and are more likely to undergo regular screening for cancer. The same phenomenon is likely to explain the lower risk of breast and cervical cancers in the same group.

The new study is consistent with most previous research, says Kallen, noting that while some studies have found a small increased risk in cancer for some subgroups of women using fertility treatment, others cannot find any risk. (More on Time.com: Breast-Feeding after Breast Cancer Is O.K.)

“It’s a really neat study,” says Dizon. “The fact that it was a large prospectively followed group is a very strong plus.”

The study also did not find any increased risk of cancer in women undergoing IVF over age 30, compared with younger women. However, it could not determine whether repeated cycles of IVF affected cancer risk, nor could it provide data on the risk in women who underwent fertility treatment but did not conceive. The average age at which participants underwent treatment was 32, and the average follow-up period was eight years, which means that the study would not have captured cancers that occurred later in life.

“One should have the caveat that these women are not very old yet; they’re mainly premenopausal. What happens at a higher age, we don’t know yet,” Kallen concedes. “Common sense says that if you increase risk because of hormonal treatment, that should appear rather quickly, within 10 years. You wouldn’t expect to see it 20, 30, 40 years later, but you never know.”

More on TIME.com:

What Happens to Elizabeth Edwards’ Kids?

Developing an Artificial Ovary

When to Give Up on IVF