Women who have their last child in their 30s or 40s have a much lower risk of endometrial cancer than women who stop having kids by 25, according to a new study.
US researchers say women who have a baby after their 40th birthday are 44 percent less likely to get endometrial cancer, which develops in the lining of the uterus.
Women who have their last baby between the ages of 35 and 39 have a 32 percent decreased risk, while women aged 30-34 have a 17 percent lower risk.
Researchers at the University of Southern California's Keck School of Medicine reviewed 17 studies involving more than 8,600 women with endometrial cancer and more than 16,500 women without it.
They analysed the impact that childbearing years have on women's cancer risk, after taking into account other risk factors such as contraception use and number births.
The study found the risk of endometrial cancer decreases by about 13 percent for every five years women delay having their last baby after the age of 30.
"While childbearing at an older age previously has been associated with a lower risk of endometrial cancer," said study leader Wendy Setiawan, assistant professor of preventative medicine.
"The size of this study definitively shows that late age at last birth is a significant protective factor after taking into account other factors known to influence the disease — body weight, number of kids and oral contraceptive use, Setiawan said in the media release.
She said older mothers had "protection" from endometrial cancer that lasted many years.
"This study shows an important protective factor for endometrial cancer, and when the exact mechanism by which it protects women from getting the disease is known, it can help our understanding of how endometrial cancer develops and thus how to prevent it," she added.
The researchers are still unsure exactly how later childbirth lowers the risk, but they think hormones from pregnancy could have a preventative effect. It's also possible that childbirth removes cancer-causing cells from the uterus.
Endometrial cancer is the most common gynaecological cancer in Australia. It affects one in 69 women and the average age of diagnosis is 64.
According to a Daily Mail report, prior research has found women who have babies later are at higher risk of ovarian cancer and breast cancer, which suggests having babies later is not enough to protect women from cancer.
The study was published online for the American Journal of Epidemiology.