When you take progesterone orally, the absorption is inefficient. This is because the liver converts the progesterone (first-pass effect) into its relatively weak metabolites (e.g. pregnandiol-3-glucoronide). Thus very little progesterone actually reaches the uterus where it is needed to facilitate pregnancy.
There is a micronized version of progesterone that is better absorbed orally than the regular version (Prometrium). An oral dose of 300 mg may result in a systemic dose of 5 to 10 ng/mL. This level is good for a post-menopausal woman for management of menopausal symptoms. However, in a fertility patient these levels are insufficient.
Oral progesterone also has the disadvantage of making you sleepy. This is the reason why we are not able to use even higher doses of progesterone orally in order for it to be effective.
At least two studies have shown significantly lower success rates in IVF patients that were on oral progesterone vs. intramuscular progesterone. Other studies have compared oral progesterone vs. vaginal progesterone and once again the pregnancy rates were lower with the oral route.
Although the majority of patients would prefer the oral route, most of us would choose the treatment option that results in a higher pregnancy rate. This is the reason why most successful IVF clinics prescribe progesterone as a vaginal suppository or intramuscular injection.
To see a fertility specialist who is a board-certified physician with high success rates, make an appointment at one of InVia’s four Chicago area fertility clinics.