Gestational diabetes does not increase breast cancer risk, major Danish study finds

Women who develop gestational diabetes are not more likely to be diagnosed with breast cancer later in life, according to a study of nearly three-quarters of a million mothers to be presented at the World Health Organization this year. Annual meeting of the European Association for the Study of Diabetes (EASD; Madrid, September 9-13).

Gestational diabetes, a type of diabetes that can develop during pregnancy, affects 14% of pregnant women worldwide and is becoming increasingly common, with those who are obese, have a family history of diabetes, and/or are older being at greater risk. Race and ethnicity can also affect risk.

It usually goes away after delivery. However, women who have had it are more likely to develop type 2 diabetes in the years afterward. Gestational diabetes is also associated with a higher risk of developing cardiovascular disease, metabolic syndrome, chronic kidney disease, and mental health conditions, including postpartum depression.

Insulin resistance, in which the body’s cells do not respond properly to insulin and cannot absorb glucose from the blood properly, causing blood sugar levels to rise, is a key feature of gestational diabetes and has also been linked to breast cancer.

Some studies have shown that gestational diabetes is associated with a higher risk of later being diagnosed with breast cancer. But other research has concluded that the risk of breast cancer is lower, or that there is no link at all.

Study leader Maria Hornstrup Christensen, from the Steno Diabetes Center Odense, Odense University Hospital, Odense, Denmark, said: “Breast cancer is the most common cancer and the leading cause of cancer death in women worldwide. The cost of treatment is also very high compared to other cancers.

“If we know who is more likely to develop breast cancer, we may be able to detect the disease earlier, because it will then be easier to treat. This could reduce deaths and treatment costs, and limit the psychological and physical consequences for women.”

To learn more, Dr. Christensen and colleagues used birth, patient, and other national registries to obtain information on all women who gave birth in Denmark over a 22-year period.

After excluding women with pre-existing diabetes or breast cancer, 708,121 women who gave birth between 1997 and 2018 remained in the analysis.

A total of 24,140 (3.4%) women were diagnosed with gestational diabetes in one or more pregnancies. The median age at pregnancy was 28 years in both women with and without gestational diabetes.

The women were followed for a median of 11.9 years, during which 7,609 women were diagnosed with breast cancer.

Women with gestational diabetes were no more likely to develop breast cancer than women without gestational diabetes. This was seen for breast cancer in general, premenopausal breast cancer, and postmenopausal breast cancer.

This finding held when age, parity, ethnicity, income, occupation, education, and pre-existing health conditions, such as high blood pressure, were taken into account.

Analyses that took into account pre-pregnancy BMI, smoking during pregnancy, and obstetric complications such as pre-eclampsia also failed to find an association between gestational diabetes and breast cancer.

The authors conclude that the study, one of the largest of its kind, did not demonstrate that gestational diabetes is associated with an increased risk of breast cancer.

Dr Christensen, who divides her time between research and her work as a midwife specialising in the care of women with diabetes, said: “It will be reassuring for women who have had gestational diabetes to know that they are not at increased risk of developing breast cancer.

However, they should be aware that they have a higher risk of certain conditions, including type 2 diabetes.

“And all women, whether or not they have had gestational diabetes, should be aware of their breasts and check them regularly for changes.”

She adds that the women studied were predominantly white and lived in a country with free health care and free breast cancer screening, so the findings may not necessarily apply to other populations and health systems.