This study examined whether progesterone levels affect pregnancy rates during in vitro fertilization.

Hormone levels are vitally important to the proper functioning of the female reproductive cycle. Estrogen (a female hormone) rises as the time of ovulation (release of an egg from the ovary) nears. This surge in estrogen causes a rise in luteinizing hormone, a hormone that stimulates the release of the egg from the ovary. Progesterone (a hormone involved in the menstrual cycle) levels rise following ovulation, preparing the uterus for possible fertilized egg implantation and pregnancy. If pregnancy occurs, human chorionic gonadotropin is produced which leads to continued progesterone production.

Women undergoing in vitro fertilization control hormone levels to carefully time ovulation, so that eggs can be harvested before they are released (egg retrieval). However, treatments that block the luteinizing hormone surge and administration of human chorionic gonadotrophin to trigger ovulation can also lead to increases in progesterone beyond normal levels. This increase may occur too early to support implantation. Whether or not progesterone levels can be too high to support a pregnancy is unknown. The current study examined how progesterone levels affected pregnancy outcomes during in vitro fertilization.

In this study, 186 women underwent in vitro fertilization treatments that included blocking the luteinizing hormone surge, a human chorionic gonadotropin ovulation trigger and progesterone supplementation following egg retrieval. Hormone levels (estrogen, luteinizing hormone, progesterone) were measured at the start of the cycle, at the time the luteinizing hormone blocker was administered, at the time human chorionic gonadotropin was administered, and at the time of egg retrieval.

In total, 33% of women achieved pregnancy, 2% miscarried, and 62% failed to get pregnant. Progesterone levels at the time of egg retrieval only were associated with pregnancy outcome. Progesterone levels on the day of egg retrieval were, on average, significantly lower in women who achieved pregnancy (7.8 ng/mL) than in women who did not (10.2 ng/mL).  Implantation rates of those with progesterone levels below 12 ng/mL on the day of egg retrieval were 43.9% versus 31.6% in those with levels above 12 ng/mL.  Clinical pregnancy rates of those with progesterone levels below 12 ng/mL on the day of egg retrieval were 38.6% versus 20% in those with levels above 12 ng/mL.

Of the women who achieved pregnancy, 75% had progesterone levels less than 10.6 ng/mL. None of the women with progesterone levels greater than 18.1 ng/mL achieved pregnancy.  As progesterone levels increased, pregnancy rates decreased. In particular, there appeared to be a steeper decline in pregnancy rates once progesterone levels were above 12 ng/mL. This may suggest that this is a clinically important level beyond which pregnancy is less likely.

This study concluded that the progesterone levels on the day of egg retrieval can affect the success of in vitro fertilization, as higher progesterone levels were associated with lower rates of pregnancy.

The study found considerable overlap in progesterone levels between those who did and didn’t conceive, and therefore these values should only be used as a guide in counselling.