Pro & Con: Does minimal or mild endometriosis cause infertility? (Opinion).

YES

There is evidence for a causal relationship between endometriosis and infertility. The prevalence of endometriosis is higher in subfertile women compared with fertile women. Secondly, an increased proportion of subfertile women have moderate to severe endometriosis compared with fertile women.

If you control for male factor infertility and coital behavior, women with minimal or mild endometriosis have lower monthly fecundity rates and lower cumulative pregnancy rates compared with women with a normal pelvis. Results of in vitro fertilization are more controversial, but there are some data suggesting a reduced implantation rate per embryo in women with endometriosis, especially in those with moderate to severe disease, compared with controls.

I think the most convincing evidence is that if you treat endometriosis, fertility improves, as seen in the Canadian Endocan study. The study conducted by the Canadian Collaborative Group on Endometriosis (N. Engl. J. Med. 337[4]:26970, 1997), showed a tendency toward reduced fertility in women with minimal to mild endometriosis.

Three controlled studies in women treated with donor sperm insemination conducted in the 1980s all found a monthly fecundity rate of about 4%-6% in women with minimal or mild endometriosis, which is significantly lower than the 15%-20% monthly fecundity rates in women with a normal pelvis. The cumulative pregnancy rate was 20%-38% in women with early-stage endometriosis, compared with 55%-80% in those with a normal pelvis. These data mean that if you control for coital behavior and for male factors, the data clearly show a tendency toward a significant difference in fertility between women with a normal pelvis and those with minimal or mild endometriosis.

A 1997 metaanalysis of data on more than 5,000 women treated with insemination of sperm from their husbands found that approximately half as many patients with endometriosis achieved pregnancy compared with women with a normal pelvis. That finding was confirmed in a large and very elegant controlled study in 1998. The same holds true if you look at implantation rates. So these studies show a dear association between minimal or mild endometriosis and infertility.

What about in vitro fertilization? Based on data, it seems that there is a decreased implantation rate in women with moderate to severe endometriosis. Overall, there are some very interesting data suggesting that moderate to severe disease may have an effect on egg quality.