Luteal phase support using micronized vaginal progesterone as pessaries or capsules in artificial cycles: is there any difference?

Research question: Is there a difference between the proportion of patients with serum progesterone <8.8 ng/ml on the day of embryo transfer when micronized vaginal progesterone (MVP) for luteal phase support (LPS) is given as pessaries versus capsules? Design: This retrospective, matched -cohort, single -centre study compared pessaries (Cyclogest) versus capsules (Utrogestan, Progeffik) for LPS in hormone replacement treatment -embryo transfer (HRT-ET) cycles. Patients under 50 years old with a triple -layer endometrial thickness of >6.5 mm underwent transfer of one or two blastocysts. Serum progesterone concentrations were measured on the day of transfer; patients with concentrations <8.8 ng/ml received a single 'rescue' dose of additional progesterone by subcutaneous injection. Results: In total 2665 HRT-ET cycles were analysed; 663 (24.9%) used pessaries for LPS and 2002 (75.1%) used capsules. Mean serum progesterone concentrations with standard deviations on the day of embryo transfer were significantly higher in the group using MVP pessaries compared with those using capsules (14.5 +/- 5.1 versus 13.0 +/- 4.8 ng/ml; P = 0.000). The percentage of participants with suboptimal serum progesterone concentrations on the day of embryo transfer (<8.8 ng/ml) was significantly lower in the pessary group than the capsule group (10.3%, 95% confidence interval [CI] 7.9-12.6% versus 17.9%, 95% CI 16.2-19.6%; adjusted odds ratio 0.426, 95% CI 0.290-0.625; P = 0.000). No differences in pregnancy outcome were observed between the groups. Conclusions: Using MVP pessaries rather than capsules for LPS resulted in significantly fewer patients having suboptimal serum progesterone concentrations on the day of embryo transfer. Consequently, almost 50% fewer patients in the pessary group needed rescue treatment.