Obese women have alterations in the environment around the ovary before they ovulate that appear to play a role in the well-documented association between obesity and reduced fertility, according to a report in the Journal of Clinical Endocrinology and Metabolism.

"Characteristics of eggs are influenced by the environment in which they develop within the ovary," lead author Dr. Rebecca Robker, from Adelaide University, Australia, said in a statement. "Our study found that obese women have abnormally high levels of fats and inflammation in the fluid surrounding their eggs, which can impact an egg's developmental potential."

The study included 96 women who were attending a private infertility clinic and who were divided, roughly equally, into normal weight, overweight, and obese groups using standard body mass index criteria. The fluid surrounding the ovaries - the follicular fluid — obtained during egg retrieval, was analyzed for hormones, metabolites, gene expression within certain cells.

As body mass index rose, so did follicular fluid levels of insulin, lactate, triglycerides, and C-reactive protein. Levels of sex hormone binding globulin, by contrast, decreased. Small differences in insulin-regulated genes in granulosa cells were also noted between obese and normal weight women.

Exactly how these local environmental changes impact ovarian function, egg quality, or both remains to be studied, "but are likely to be significant," the authors conclude.

SOURCE: Journal of Clinical Endocrinology and Metabolism 2009.