P-648 Intramuscular progesterone as a rescue therapy for optmized luteal phase support in patients with low progesterone levels during elective euploid single embryo transfer

Abstract

Abstract Study question Does the addition of intramuscular progesterone(P) may improve the clinical outcomes of FET cycles in cases of low serum P levels before embryo transfer? Summary answer Intramuscularly P may correct the potentially harmful effects associated with low serum P levels during the luteal phase in FET cycles performed under HRT. What is known already Compelling evidence suggests that during FET, P levels measured on the mid-luteal phase may impact pregnancy outcomes, indicating that regardless of uterine P levels, a minimum level of serum P is required to enhance clinical outcomes. Up to one-third of patients under HRT using intravaginal micronized progesterone during FET cycles may present inadequate serum P levels, which may decrease the live birth rate in up to 32% when compared to patients with adequate serum P levels. Thus, the individualization of the LPS according to P monitoring may be necessary to overcome the deleterious effect of low P levels before FET. Study design, size, duration A retrospective cohort study was conducted between August 2019 and June 2021. Patients undergoing elective single embryo transfer (eSET) of euploid day 5 or day 6 blastocysts with own oocytes were included in the study. During the study period, 305 patients fulfilled the inclusion criteria. Participants/materials, setting, methods In patients presenting with serum P levels <9.2 ng/mL on the day before the ET, 1 mg/day of intramuscular P was added as a rescue therapy on the day of the ET and was maintained until the blood pregnancy test was completed; this represented the rescue LPS (rLPS) group. The clinical outcomes of rLPS group were compared to those patients with adequate serum P levels that maintained the LPS with vaginal micronized P (tLPS group). Main results and the role of chance During the study period, 305 patients fulfilled the inclusion criteria. There were 198 patients (65%) with adequate serum P levels that maintained the LPS with vaginal micronized and oral P (tLPS group), while 107 patients (35%) presented with low P levels in which a rescue intramuscularly administered P was added on the day of the embryo transfer (rLPS). When comparing the groups, there was no statistical difference in terms of maternal age, BMI, endometrial thickness before starting the P administration, estradiol and P levels in the proliferative phase, E levels in the luteal phase. There was a statistically significant difference in P levels on the day before the embryo transfer when comparing the tLPS and rLPS groups (13.6±6.2 ng/mL and 7.5±1.9 ng/mL, respectively; P<0.0001). No significant difference was observed in the clinical outcomes when comparing the tLPS and rLPS. The pregnancy rates were 73.7% and 72.0% (aOR=0.91, 95% CI 0.54–1.55; P=0.74), clinical pregnancy rates were 69.2% and 68.2% (aOR=0.96, 95% CI 0.58–1.55; P=0.86), and ongoing pregnancy rates were 65.7% and 64.5% (aOR=0.95, 95% CI 0.58–1.55; P=0.84) in the tLPS and rLPS respectively. The multivariate logistic regression did not identify any independent factor related to the ongoing pregnancy rate. Limitations, reasons for caution A control group comprising patients with low P levels that did not receive any intervention is lacking. However, we believe it would be unethical to neglect evidence from previous studies suggesting that low P levels might reduce reproductive outcomes in this group of patients. Wider implications of the findings Although previous clinical studies concluded that low luteal P levels before FET might impact clinical outcomes, we observed that intramuscular P administration starting on the day of euploid blastocyst ET, as a novel rescue therapy, can lead to comparable results to those achieved in patients presenting with adequate P levels. Trial registration number -