Women who develop melanoma during their pregnancy or within one year of it are more likely to die from the disease, a new study suggests.

Specifically, women diagnosed with malignant melanoma during their pregnancy or within one year of giving birth were 5.1-times as likely to die, 6.9-times as likely to experience metastasis, and 9.2-times more likely to have a recurrence, compared with non-pregnant women, the new study showed. Researchers suspect that pregnancy hormones may fuel the aggressive cancer.

“We saw significant, worse prognoses and outcomes for women with a pregnancy-associated melanoma, compared to a control group of non-pregnant women,” says Brian Gastman, M.D., a plastic surgeon, director of melanoma surgery at Cleveland Clinic, and primary investigator on the study, in a news release. “The rate of metastasis, recurrence and death in our findings were astounding — as the rates were measurably higher in women who were diagnosed with melanoma while pregnant, or within one year after delivery.”

The new case-control study included 462 women aged 49 years or younger with cutaneous melanoma. All female patients with a biopsy-proven diagnosis of melanoma between 1988 and 2012 were included in the study, while patients with a follow-up of less than two years were excluded.

The findings appear online in the Journal of the American Academy of Dermatology.