Women who suffer miscarriages and those who have full-term pregnancies could be at less risk of developing a common kind of cancer, a new study has found.
Researchers from the Queensland Institute of Medical Research (QIMR) Berghofer said the risk of endometrial cancer reduced by about 15 per cent with each pregnancy, for as many as eight pregnancies.
For miscarriages, that risk falls by about 7 per cent per miscarriage.
Endometrial cancer, also known as uterine cancer, affects the endometrium — the lining of the uterus or womb — and is the fifth most common cancer for Australian women.
Cancer Australia said the disease affected 3,115 women across the country in 2019, and claimed about 350 lives in 2018.
QIMR Berghofer researchers examined pregnancy data from 30 studies conducted in Australia and around the world by the Epidemiology of Endometrial Cancer Consortium.
This included 16,986 women with endometrial cancer and 39,538 women who never had the disease.
The research was led by Penelope Webb, the head of QIMR Berghofer Medical Research Institute’s Gynaecological Cancers group.
“It’s well known that having a full-term pregnancy reduces a woman’s risk of developing endometrial cancer,” Professor Webb said.
“But our research has shown that not only does each additional full-term pregnancy reduce that risk by about 15 per cent, the reduction continues for up to at least eight pregnancies.
“We have also clearly shown for the first time that pregnancies that end in a miscarriage also reduce risk of endometrial cancer by about 7 per cent.”
Women who give birth to boys at lower risk
Susan Jordan, the first author of the study and now an associate professor at the University of Queensland School of Public Health, said the findings questioned the long-held belief that only hormone levels in the last trimester provided protection against women’s cancers.
“While a full-term pregnancy is associated with the greatest reduction in risk for endometrial cancer, even pregnancies that end in the first or second trimester appear to provide women with some protection,” she said.
“This suggests that very high progesterone levels in the last trimester of pregnancy are not the sole explanation for the protective effect of pregnancy … early pregnancy factors may also be playing a protective role against this disease.”
Brisbane mother Lily Dean, who is pregnant with her second child, described the QIMR Berghofer findings as “surprising”.
“Most of the time all that mothers hear about are the terrible things that happen to your body when you’re pregnant,” Ms Dean said.
“The miscarriages part is very surprising, I would have thought it would be full-term only.”
Ms Dean, 23, said she and her 26-year-old husband Rodney found out yesterday that their two-year-old son Archie would have a brother when their second child is born next March.
The researchers found women who had only boys, like Ms Dean, had a lower risk of endometrial cancer than mothers of only girls.
A mix of boys and girls also lowered the risk, the study said.
Dr Jordan said the study would help ongoing research into cancer prevention for Australian women.
“This raises the need for more research to identify other factors that underlie this protective effect,” she said.
In a statement, Cancer Council Queensland CEO Chris McMillan said the charity welcomed research into endometrial cancer, which about 450 women are diagnosed with in Queensland every year.