Progesterone shot improves chances of live birth with frozen embryo

Women undergoing frozen embryo transfer (FET) appear to have reduced live birth rates after vaginal-only progesterone replacement, a study reports. However, add-on intramuscular progesterone injection helps increase the live birth rates, with the every-third-day regimen being as good as the daily dosing schedule.

Researchers looked at 1,346 women planning vitrified-warmed transfer of high-quality nonbiopsied blastocysts. Of these, 1,125 women were randomly assigned to one of the following interventions in preparation for FET: 50 mg of intramuscular progesterone daily (control), 200 mg of vaginal micronized progesterone twice daily plus 50 mg of intramuscular progesterone every third day (combination treatment), or 200 mg twice daily of vaginal micronized progesterone.

All women completed a survey to assess their experience and attitudes regarding the route of progesterone administration. They also underwent a serum human chorionic gonadotropin test 2 weeks after FET.

In total, 1,060 FETs were completed. The primary outcome of live birth rate per vitrified-warmed embryo transfer was markedly higher in the groups that received intramuscular progesterone than in the group given vaginal progesterone only (44 percent and 46 percent vs 27 percent, respectively).

Half of the pregnancies in women receiving only vaginal progesterone ended in miscarriage.

The findings underscore that intramuscular progesterone every third day is an effective alternative regimen with fewer injections.