(RxWiki News) So little is understood about the effects of chemotherapy on a developing baby that doctors are still learning about how safe treatment is during pregnancy.
But a recent study suggests that treatment given to pregnant women after the first three months may not raise the risk of early birth, birth defects or delivery problems.
In fact, for mothers with breast cancer, their newborn's survival is more dependent on being born after 37 weeks.
"Ask your oncologist about chemo during pregnancy."
In a study led by Sibylle Loibl, MD, of the German Breast Group in Germany, researchers wanted to find out more about the options women might have for treatment if they are both pregnant and fighting breast cancer.
The study involved 413 women, enrolled from April 2003 to December 2011, who had early-stage breast cancer. Their average age was 33, and they were an average of 24 weeks pregnant.
Almost half of the women - 197 of them - received chemotherapy during their pregnancy with one to eight cycles (an average of four across the group).
Anthracycline was administered to 178 of the women; 15 received cyclophosphamide, methotrexate and fluorouracil, and 14 received a taxane. All of the chemo occurred after the first trimester.
They found that the birth weights of the babies born to the women who underwent chemotherapy did appear to be affected by the treatment, but there was no difference in birth weights based on the number of chemo cycles women went through.
There also did not appear to be a significant difference between the rates of premature deliveries among the women who underwent chemo compared to those who did not.
Across the 386 babies who were ultimately born, 40 of them (10 percent) had side effects, birth defects or complications, mainly in the babies who were born early (before the 37th week of pregnancy).
Almost half of the total babies were born prematurely, before the 37th week, and 31 of these 191 early babies had a side effect, birth defect or complication, compared to nine of the 195 babies born after the 37th week.
The average rate of premature births is 10 to 15 percent, so 50 percent is a higher rate among the women who had breast cancer, and 23 percent of the women gave birth before the 35th week, which is extremely early.
There were higher numbers of birth defects, side effects and complications among the babies whose mothers underwent chemo, but these appeared to be more related to premature birth than to the chemo. The higher number was not significant enough to state that chemotherapy exposure was linked to the problems the babies experienced.
There were 203 babies born to mothers who had chemo, and 31 experienced a problem. Among the 170 babies born to mothers who did not undergo chemo, seven had a complication or birth defect.
"If our findings are confirmed by other studies, breast cancer during pregnancy could be treated as it is in non-pregnant women without putting fetal and maternal outcomes at substantially increased risk," said Dr. Loibl. "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."
Although two babies born to mothers who had chemo died during a premature delivery, the researchers said they do not believe the deaths were related to their mothers' treatment.
Dr. Loibl added that the number of weeks of pregnancy when a baby is born is one of the most important factors related to a newborn's health and survival.
"Our findings emphasize the importance of prioritizing a full-term delivery in women who undergo chemotherapy while pregnant," she said.
The average number of months that women lived without recurrence of the breast cancer if they received chemo while pregnant was 70.6 months, compared to 94.4 months for the women who began chemo after giving birth.
"Delay of cancer treatment did not significantly affect disease-free survival for mothers with early breast cancer," the authors wrote in their conclusion. "Because preterm birth was strongly associated with adverse events, a full-term delivery seems to be of paramount importance."
The study was published August 15 in the journal The Lancet. The research was funded by the BANSS Foundation, the Research Foundation-Flanders, Clinical Research Fund-UZ Gasthuisberg and the Belgian Cancer Plan at the Belgian Ministry of Health.
The authors also thanked the University Hospital Frankfurt and the German Breast Group for their support in the research. The authors declared no conflicts of interest.