Abstract
Study question
Does SC-P provide similar ongoing pregnancy rates (OPRs) as intramuscular progesterone(IM-P) in hormone replacement therapy (HRT)-FET cycles and do serum progesterone (P) levels on FET day effect on pregnancy outcome? Summary answer: SC-P administration had similar OPR compared to IM-P in HRT-FET cycles. In SC-P group embryo transfer(ET) day P found to be insignificant factor for outcome.
What is known already
Different P routes can be used in HRT-FET cycles such as vaginal P, IM-P and recently SC-P. Only retrospective studies evaluated the comparison of SC-P with other routes in HRT-FET cycles. Here, we assessed prospectively whether SC-P is effective for HRT-FET cycles. Previous studies reported that serum P levels on ET day after vaginal P administration clinical outcomes were closely correlated. The correlation between serum P after IM-P administration and clinical outcomes were conflicting. In addition, there is lack of data on the serum P levels after SC-P administration. Serum P levels on ET day were evaluated in this study.
Study design, size, duration
This prospective cohort study was performed between July 1-October 31 2020, enrolled 224 patients scheduled for HRT-FET cycles with SC-P(25 mg twice daily) or IM-P(50 mg once daily). The route of P was decided according to the patient’s eligibility to hospital. First FET cycle was included after freeze-all cycles for each patients. Female age>35, PGT-A cycles, cleavage ET, >1 ET, patients with uterine pathology and hydrosalpinx, FET with surplus embryos, endometrial thickness<7mm were excluded.
Participants/materials, setting, methods
Female age ≤ 35 years old with a triple-layer endometrium >7 mm underwent transfer of single blastocysts after the first ET after freeze-all cycles. The indications for freeze-all were ovarian hyperstimuation syndrome and trigger day P level>1.5 ng/ml. 224 patients were eligible for study; 133 in SC-P group and 91 in IM-P group.The primary endpoint was the ongoing pregnancy rate (OPR) beyond pregnancy week 12.
Main results and the role of chance
The demographic, cycle, embryologic characteristics were similar between groups. The median circulating P levels on the day of ET were 19.92(15.195–27.255)ng/
ml and 21(16.48–28)ng/ml in the SC-P and IM-P groups,(p = 0.786). The clinical pregnancy rates [86/133(64.7%) vs 57/91(62.6%);p=0.757], miscarriage rates [21/86(24.4%) vs 10/57(17.5%) ;p=0.329], and OPR [65/133 (48.9%) vs 47/91(51.6%); p = 0.683] were comparable between the SC-P and IM-P. Binary logistic regression was performed for ongoing pregnancy as the dependent factor blastocyst morphology was found to be the only significant independent prognostic factor (p = 0.006), whereas the route of P was insignificant. In the SC-P and IM-P 
groups, the effect of ET day P levels were divided into quartiles(Q) to evaluate the effect on ongoing pregnancy. In SC-P group OPR were similar in four Q [Q1:33.3%(11/33),Q2:50%(17/34),Q3:60.6%(20/33),Q4:51.5%(17/33) (p = 0.1)].For IM-P group; Q1 had a significantly reduced OPR than Q2, Q3, Q4. [26.1%(6/23),65.2%(15/23),54.5%(12/22) and 60.9%(14/23), p = 0.031]. Logistic regression analysis for OP was performed separately in SC-P group and IM-P group. Although in SC-P group, ET day P levels was not found to be a significant factor, in IM-P ET day P level was found to be an independent factor for OP in IM-P group (Q1vs Q2+Q3+Q4; OR: 8,178 95% CI: [1.387–48.223] p:0.02).
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Limitations, reasons for caution
Although this study has the advantage of being prospective and in a homogenous study population, randomized controlled trials are warranted to evaluate the effectiveness of SC-P to other routes of P. Extrapolation to unselected populations of this study is needed.
Wider implications of the findings: Assignment of threshold of serum P on the day of ET for HRT-FET cycles to optimize outcomes is critical for every route of P. Regarding these results, individual luteal phase for HRT-FET cycles can improve IVF outcome.
Trial registration number
None
Vitrified blastocyst transfer cycles with the use of only vaginal progesterone replacement with Endometrin have inferior ongoing pregnancy rates: results from the planned interim analysis of a three-arm randomized controlled noninferiority trial
