TUESDAY, May 17 (HealthDay News) -- A gene variation that causes faulty cholesterol regulation also appears to affect production of the pregnancy hormone progesterone and may be a reason why some women can't get pregnant, researchers say.

The Johns Hopkins University team looked at more than 200 infertile women who were undergoing in vitro fertilization (IVF) and identified nine who had the variation of the scavenger receptor class B type 1 (SCARB1) gene.

All nine women had low levels of progesterone, which plays a critical role in sustaining pregnancy in its earliest stages. These low levels of progesterone persisted even though the women were supplemented with progesterone as part of the IVF process. None of the women became pregnant after undergoing IVF.

This variation in the SCARB1 gene could be present in 8 percent to 13 percent of the population, according to study leader Dr. Annabelle Rodriguez, an associate professor of medicine at the Johns Hopkins University School of Medicine.

She and her colleagues also developed a simple blood test for the gene variation but noted there is no approved treatment for this type of infertility.

"Infertility is fairly common and a lot of the reasons for it are still unknown," Rodriguez said in a Hopkins news release. "Right now, the benefit of this research is in knowing that there might be a genetic reason for why some women have difficulty getting pregnant. In the future, we hope this knowledge can be translated into a cure for this type of infertility."

The study appears online in the journal Human Reproduction.

More information

The U.S. National Women's Health Information Center has more about female infertility.