according to lead author Christine Langton, who conducted the research as part of her PhD dissertation.
“We’re one of the larger studies to have looked at both of these contraceptive methods at the same time,” says Langton, now a PhD researcher at the National Institute of Environmental Health Sciences. “We feel we’re contributing to the story, and to the literature, though nothing we did was definitive. This is a piece of the puzzle.”
Women who experience menopause before the age of 45 are defined as early menopause, and they are at a greater risk for cardiovascular disease, osteoporosis, and dementia, among other health conditions. Oral contraceptives change hormone levels and prevent ovulation; tubal ligation may affect blood supply to the ovaries, and certain methods of the procedure may damage the ovary and surrounding neural tissue, as noted by the researchers, including senior author Elizabeth Bertone-Johnson, professor of epidemiology and Langton’s mentor.
“Recently, AMH has become an established marker for the timing of menopause and was found to be strongly associated with the risk of early menopause,” the author said. “Yet, the association of reproductive and lifestyle factors with AMH levels remains unclear.”
The team focused on a subset of 1,420 women with early menopause in the Nurses’ Health Study prospective cohort who had provided blood samples between 1996 and 1999. A history of their oral contraceptive use and tubal ligation began in 1989 and was updated every two years until their blood was collected.
“Women who reported that their [tubal ligation] procedure included the use of a clip, ring or band had significantly lower AMH levels compared to women who never had a TL procedure,” the researchers write.
Langton adds that the limitation is relatively smaller number of women reporting the type of tubal ligation.
When it came to oral contraceptives, “we saw a significant inverse association – the longer the use of oral contraceptives, the lower the AMH levels were,” Langton says. “That particular finding was a little surprising to us because it didn’t completely align with what we saw when we looked at oral contraceptives and early menopause in the larger cohort” of more than 115,000 women.
The inverse proportion between oral contraceptive use and AMH levels remained significant even after adjusting the related factors such as BMI, smoking, alcohol, number of pregnancies, and breastfeeding.
“We think further research is warranted,” Langton says.