In their first few years of life, children with prenatal exposure to their mother’s cancer or cancer treatments scored just as well on tests of cognitive development and cardiac function as children whose mothers were cancer-free, new report says.

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A cancer diagnosis is always upsetting, and that’s especially true when the patient is pregnant. A new study may reassure women that their babies can turn out fine despite exposure to the disease and the resulting treatments.

In their first few years of life, these children scored just as well on tests of cognitive development and cardiac function as children whose mothers were cancer-free, according to a report published in the most recent New England Journal of Medicine. However, the children of cancer patients were more likely to be born prematurely.

Researchers from the International Network on Cancer, Infertility and Pregnancy in Europe tackled the study because little is known about how cancer affects a fetus. Such cases occur rarely, about once per 1,000 pregnant women, according to an editorial that accompanies the study. That means a typical obstetrician will only ever face a handful of such cases. Oncologists aren’t likely to encounter many pregnant patients, either.

“Specialty-care providers find themselves in unfamiliar territory when cancer is diagnosed in a pregnant woman,” according to the editorial.

But women in the situation have to make treatment decisions, and the lack of reliable information influences their thinking, the study authors wrote.

For their study, the researchers identified 129 children who had prenatal exposure to their mother’s cancer. Among these children, 74 percent were exposed to chemotherapy in utero, 2 percent to other drug treatments and 9 percent to radiotherapy. Some children were exposed to more than one of these treatments.

In addition, 10 percent were in utero when their mothers had surgery, and 11 percent had mothers who opted not to have cancer treatments until after the birth.

Each of these 129 children was matched with a “control” child who was born at the same gestational age. In each pair, the children were the same age when they were tested for cardiac and cognitive function. All of the matched controls were born to mothers who were cancer-free.

In each group, the researchers put 47 children through a battery of heart tests when they were 36 months old. Heart rate, blood pressure and other measures of cardiac function were the same for children in both groups, and all hearts were free of structural abnormalities, the researchers found.

Cognitive function was measured at either 18 or 36 months using the Bayley Scales of Infant Development. Most children in both groups received scores in the normal range, and there were no overall differences between children with prenatal exposure to cancer and the healthy controls, according to the study.

Even when the researchers analyzed the children in separate groups based on the type of cancer treatment they weathered in utero, they found no significant differences compared to the healthy controls.

The children of the cancer patients were different in one important respect: They were much more likely to be born prematurely. Among the 129 children in the study, 11 were very preterm (born between 27 and 31.9 weeks’ gestation), 16 were moderately preterm (born between 32 and 33.9 weeks) and 52 were late preterm (born between 34 to 36.9 weeks).

Altogether, 61 percent of these children were born prematurely. That compares with preterm birthrates of 7 to 8 percent in the countries where these children were born (Belgium, the Netherlands, Italy and the Czech Republic). The earlier the children were born, the lower their scores on the cognitive-function tests, the study authors found.

In addition, 25 percent of the children exposed to chemotherapy and 36 percent of those exposed to radiotherapy were considered small for their gestational age. In the control group, 15 percent of children got this designation, according to the study.