Progesterone is the main drug and hormone that in fact supports pregnancy. Its role in IVF is to support the second stage of pregnancy where the embryos are implanted, and in frozen cycles, as well as the donor cycles, progesterone becomes the main hormone that supports pregnancy.
There has been a huge debate whether progesterone has to be used as a vaginal preparation or injectable format. Multiple studies have been published, some indicating there is no difference in this treatment, while others indicate that the injections may be better.
A study was done when the progesterone was used in oocyte donation cases. There was some evidence showing lower progesterone levels at the time of transfer in oocyte donation cycles concerned with higher miscarriage rates, so in these cases, women who received oocytes were given either vaginal progesterone, and if they were pregnant, they were given an injectable weekly progesterone which is not available in the UK. Later on there was another group that was given weekly progesterone along with vaginal progesterone after embryo transfer, and in fact what was seen is that if you gave intramuscular throughout from embryo transfer, the live birth rates were the maximum, and in fact if you did not give any intramuscular progesterone, the live birth rates dropped to less than 16 per cent, while when you gave progesterone when HCG was positive, the live birth rate went up to 24 per cent.
Thus the evidence came up from this study that if you were to give injectable progesterone, the rate of miscarriage would drop as well as the chance of having a live birth rate was much better. It is likely that women having egg donation may suffer from prolonged hormonal deficiency, and in fact progesterone may decrease the uterine contractions. Thus progesterone may give us a much better chance of pregnancy, and giving injectable progesterone may increase the same progesterone levels and have a better impact.