Scientists have discovered that radiotherapy during childhood increases a woman's risk of losing a baby.
Pregnant women who had radiation treatment to the pelvic region in earlier years, must have "careful management" as the risk up of stillbirth or infant death for is increased by up to 12 times.
Scientists in the US said that the stillbirths are thought to be affected by the radiation that may affect the blood flow and growth of the womb.
The researchers, from the International Epidemiology Institute in Rockville, Maryland, wrote in an online edition of The Lancet: "For women high-dose uterine or ovarian radiation does seem to have important adverse effects, which are most likely to be attributed to uterine damage.
"Therefore, careful management is warranted for pregnant women treated with high doses of pelvic irradiation before they have reached puberty."
Radiotherapy for testicular cancer in young boys had no similar impact, the study, led by Professor John Boice, showed.
The study was conducted using information from the Childhood Cancer Survivor Study to calculate the risk of stillbirth and infant death among the offspring of men and women who had cancer treatment in their childhood.