Researchers from the University of North Carolina-Chapel Hill found the health risks of newborns born to women with breast cancer varied depending on the mother’s type of cancer.

Findings were published online Jan. 4 in the International Journal of Cancer. Study authors analyzed health indicators for children of young breast cancer survivors for four health markers. These included whether newborns were born preterm (less than 37 weeks), normal weight, small for gestational age and delivered via C-section.

There was no increase in the prevalence of these health indicators in newborns across all breast cancer types. But when researchers broke down data by cancer type, they found an increased risk of preterm birth, low birth weight and C-section delivery for women with estrogen receptor-negative breast.

The study included 4,978 cases of women diagnosed with breast cancer in North Carolina between 2000 and 2013. Data were taken from the North Carolina Central Cancer Registry. For women with estrogen receptor-negative breast cancer, 18 percent of births were preterm compared to a rate of nearly 10 percent across the entire state. The team pointed out that a larger number of patients needed to be examined to ensure their findings.

"The good news is that overall, women who conceived after their breast cancer diagnosis did not have an increased risk of preterm birth," said Hazel B. Nichols, PhD, an assistant professor in the UNC Gillings School of Global Public Health, in a university press release. "However, when we looked more closely, we saw that women with estrogen receptor-positive breast cancer didn't have an increased risk of preterm birth, but women with estrogen receptor-negative breast cancer did—and it was almost twice as high. What we need to do next is to see if this same finding is replicated in larger studies."

Compared to the general population, the overall rate of live births was about 57 percent lower in women with breast cancer compared to those who did not have breast cancer, study authors noted.

The low birth rate may be attributed to the estrogen-specific targeting in women with estrogen receptor-positive breast cancer as well as the five-year treatment period recommended in patients to prevent cancer recurrence.

For Nichols, the findings drove home the importance of fertility counseling in breast cancer patients who may want to conceive.

"There are very consistent recommendations that women who are diagnosed with breast cancer should be counseled before they're treated about any potential risks of their cancer treatment on future fertility," Nichols said. "I think we need to do a better job making sure all women with cancer get the information they need before they start their treatment."