A recent Danish study found that oral contraceptives, when taken under six months before conception or even during pregnancy, can be linked to an increased risk of childhood leukemia.

The study tracked 1.1 million Danish children over the course of nine years and estimated 25 cases of leukemia in Denmark that could be attributed to maternal hormonal contraception. As Medscape reports, the risk of leukemia in children was found to be 78 percent higher when mothers used hormonal contraceptives than when they did not.

Results revealed that this particular risk factor was only consistent with contraceptives containing progestin and estrogen but not with progestin-only contraceptives. If an individual stopped taking contraception more than six months before their pregnancy, the risk was not statistically significant.

It remains evident that hormonal birth control can cause cancer in women. Dr. Marie Hargreave and her colleagues who co-authored the study, wrote, “Sex hormones are considered to be potent carcinogens, and the causal association between in-utero exposure to the oestrogen analogue diethylstillbestrol and the subsequent risk for adenocarcinoma of the vagina is firmly established.”

An empty birth control pill pack.

Regarding the implications on child leukemia, the study continued that, “The mechanism by which maternal use of hormones increase cancer risk in children is, however, still not clear.”

Since almost no risk factors have been scientifically established for the causes and prevention of childhood leukemia, this study sets an important precedent for further medical inquiry.

Hormonal contraceptives are still a recommended birth control method for women, but future studies may better inform how long mothers should cease taking the pill prior to childbirth. Further research may also incite a push for non-hormonal contraceptives.

For now, science maintains that oral contraceptives are still safe despite their findings because the numbers affirming the link are relatively small. The absolute risk for childhood leukemia remains low.