LONDON — Researchers have encouraging news for women who are diagnosed with cancer while pregnant. Studies suggest that these women can be treated almost the same as other cancer patients are, with minimal risk to the fetus.

Only about 1 in 1,000 pregnant women face this dilemma, but doctors fear more will because the risk of cancer rises with age, and more women are delaying having children until they're older.

Doctors have long worried about how to balance treating a pregnant woman with cancer and the need to protect her fetus from the effects of toxic-cancer drugs and radiation treatments. A series of papers in the journals Lancet and Lancet Oncology published Friday make several key contributions:

• A Belgian-led study of 70 children in Europe exposed to chemotherapy while they were in the womb found they developed just as well as other children, according to tests on their hearts, IQ and general health. They were assessed at birth, 18 months and every few years until age 18.

• Chemotherapy after the first trimester is possible, using extra ultrasounds to ensure the baby is developing properly. Radiation therapy is best done in the first two trimesters, according to a review of previous studies, led by Belgian researchers.

• Ending the pregnancy doesn't improve chances for the mother, the same study found.

• The type of cancer seems to matter: An Israeli analysis of past research suggested pregnant women with blood cancers might want to terminate an early pregnancy when chemotherapy can't be delayed.

"Many (doctors) aren't keen to give chemotherapy to pregnant women and may even recommend termination," said Dr. Frederic Amant of the Leuven Cancer Institute in Belgium, an author of two of the papers. "But treating a pregnant woman with cancer doesn't have to be so different from treating a cancer patient who isn't pregnant."

Amant, who led the study of 70 children, said that most of the children with cognitive problems were born premature and that was probably the primary cause of their delayed development.

Dr. Richard Theriault, a professor of medicine at the MD Anderson Cancer Center in Texas, said he hoped the papers would change how doctors treat pregnant cancer patients.

"Terminating a pregnancy is not always necessary," Theriault said.

He said the placenta seems to act as a kind of filter for chemotherapy drugs, restricting their effects on the fetus.