Chemotherapy pregnancy has no adverse effects on the newborn, according to a new study.

Researchers say that breast cancer treatment is possible during pregnancy and that women do not need to opt for pre-term delivery to begin their cancer treatment.

For the study, researchers assessed pregnancy outcomes in 400 European women who were diagnosed with early-stage breast cancer while they were pregnant. Of these, 48 percent, around 197 women, underwent chemotherapy during pregnancy.

The researchers found that babies born to women who underwent chemotherapy had no higher risk of birth defects, higher blood pressure disorders or alopecia. The babies, however, had a lower birth weight than babies born to women who did not undergo chemotherapy.

Researchers also found that the number of cycles of chemotherapy didn't affect the newborns birth-weight.

"If our findings are confirmed by other studies, breast cancer during pregnancy could be treated as it is in non-pregnant women without putting foetal and maternal outcomes at substantially increased risk," said professor Sibylle Loibl, of the German Breast Group, one of the researchers in a news release.

In the study, almost 50 percent of the deliveries were pre-term whereas in the general population, the prevalence of pre-term birth is about 10-15 percent. Also, about 23 percent of the deliveries occurred before the 35th week. The complications that were reported in babies were mostly due to premature birth and not due to chemotherapy, researchers said.

"Our findings emphasise the importance of prioritising a full-term delivery in women who undergo chemotherapy while pregnant," said Professor Loibl, in a press release.

According to American Cancer Society, an estimated 1 out of every 1000 pregnant women is diagnosed with breast cancer.

Previous studies have shown that breast cancer treatment (for first stage breast cancer) does not affect pregnancy outcomes and that it is safe for women to undergo these treatments even if she's pregnant.

"Illness and mortality in newborn babies is directly related to gestational age at delivery. This is an important clinical message because the decision to deliver the foetus preterm is often taken without medical indication. Our work suggests that treating patients with breast cancer while pregnant is possible, and there is no need to interrupt the pregnancy or receive inferior therapy," said professor Loibl.

Pregnancy causes hormonal changes in the body and breaks the menstrual cycles for a while. Women who have babies at young age and those who have many babies may be at a lower risk of developing breast cancer.

The study was published in The Lancet Oncology.