As treatment for cancer steadily improves, the number of cancer survivors increases.

There are already an estimated 15.5 million cancer survivors in the United States, and this number is predicted to rise to 20 million by 2026.

One of the major concerns of women who survive cancer is their ability to have children later in life. Certain chemotherapy treatments and radiation therapy can affect fertility levels. For younger cancer survivors, for whom egg collection is not an option, this is particularly concerning.

Despite these worries, little research has been dedicated to looking at the impact of cancer treatment on the children of women treated for cancer during their childbearing years.

Cancer survivors and future pregnancies

A team of researchers set out to investigate this question. The study's lead author was Hazel B. Nichols, Ph.D., assistant professor in the University of North Carolina Gillings School of Global Public Health in Chapel Hill.

To examine any interactions between cancer treatment and later pregnancies, the researchers delved into birth certificate data from North Carolina. They concentrated on patients who were diagnosed with cancer while aged between 15 and 39, from 2000 to 2013. They looked at the health outcomes of the firstborn children of these mothers. In all, 2,500 babies born from cancer survivors were assessed.

Once the data had been analyzed, the team found that children born to cancer survivors were more likely to be born early - before the 37-week mark - than women who had not had cancer (13 percent compared with 9 percent).

Although this difference is relatively small, because babies born early are more likely to have complications, it is certainly worth being aware of. However, Nichols is quick to note that not all babies born early will face health problems:

"It's a risk factor; it doesn't mean that someone who is born preterm is going to develop future health problems, but children who don't spend as long in utero can have a higher incidence of breathing problems or infections. This is something for women and their providers to be aware of when a woman is reviewing her prenatal care, or talking about her medical history with her provider."

The study also showed that babies of cancer survivors were more likely to have a lower birth weight and be born by cesarean section.

Breaking down the data

When the researchers broke the data down into specific cancer types, they found that survivors of breast cancer had almost twice the risk of preterm birth than women who had not had cancer.

Similarly, there was a 60 percent higher risk of preterm birth in women who had survived Hodgkin lymphoma, roughly double the risk with non-Hodgkin lymphoma, and an almost threefold risk increase with gynecologic cancers.

Preterm birth and low birth weight risk were highest in women who were diagnosed with cancer while pregnant. Potentially, this might be because they delivered early so that they could begin treatment as soon as possible. However, this may not be the only factor at work; the analysis also showed that women diagnosed with cancer before the start of pregnancy had a similar increase in risk.

When the data were split into treatment types, they found that women who underwent chemotherapy were more likely to have preterm births and, to a lesser extent, cesarean sections. This is an area that Nichols would like to investigate further. Researchers would like to be able to break down chemotherapy in a more detailed way, she says:

"Chemotherapy is a very broad category, and the agents have very different effects on the body. In the future, we'd like to get more detailed information on the types of drugs that were involved in treatment."

Although the findings are concerning, there are also positives to be taken from the data, as Nichols says: "One of the things that's exciting about this work is we identified thousands of women who went on to have a child after they were diagnosed and treated for cancer."

The findings bring hope, but they also bring home the importance of disseminating the right information at the start of cancer treatment and beyond. She continues:

"We know that cancer treatment can have an impact on fertility, and it's only after puberty that some of the options exist to either freeze eggs or freeze embryos, or take other steps to protect fertility. So this is a time period when it's important to counsel women on what their reproductive risks are for cancer therapy, or what they can expect in the future."