P-410 A modified artificial cycle-frozen embryo transfer(mAC-FET) protocol with evidence of corpus luteum(CL) formation as determined by serum relaxin-2 in early pregnancy :a prospective proof-of-concept study

Abstract Study question Can a mAC-FET protocol for endometrial preparation in ovulatory patients lead to formation of a CL as evidenced by serum relaxin-2 in the pregnant patients? Summary answer CL forms in the mAC-FET protocol as serum relaxin-2 in early pregnancy was comparable to that in spontaneous conception.Late luteal rise of relaxin-2 wasn’t demonstrated. What is known already Clinical evidence points to increased incidence of preeclampsia in pregnancies by AC-FET cycles compared to ovulatory FET cycles-natural cycle(NC) and mNC. The absence of CL and it’s secretory products like relaxin-2 is a contributing factor. FET protocols for endometrial preparation in ovulatory patients need to be optimised. NC/mNC-FET protocols need frequent monitoring. Also there is a temporal variability between LH/hCG and progesterone levels. We studied a mAC-FET protocol in ovulatory patients with a delayed start(day3-5 of the cycle),low dose transdermal 17β estradiol gel to see the formation of CL as elucidated by the presence of serum relaxin-2 in early pregnancy. Study design, size, duration A proof-of- concept prospective study was conducted at a tertiary centre (July2023-Dec2023). Serum relaxin-2(R&D/Quantikine/ELISA) was determined in 4 groups of patients- Group-A. mAC-FET(n = 34) 1.On the day of start of progesterone 2.Post-ET day5-9 (along with serum progesterone) 3.In pregnancy(6-9 weeks of gestation) Group-B. AC-FET(n = 8) 1.On the day of start of progesterone 2.In pregnancy(6-9 weeks) Group-C. Spontaneous conception (n = 9) 1.In pregnancy(6-9 weeks) Group-D. Infertility patients ( n = 24) 1.Preovulatory. All patients were ≤40 years with a BMI ≤30kg/m2. Participants/materials, setting, methods In the AC-FET cohort-oral estradiol 6mg/day was started from day1/2 of the cycle. When endometrial thickness was>7mm,progesterone<1ng/ ml then intramuscular progesterone was started- 50mg/day-3 days,100mg on day4-the day of ET(Day-3 embryos) and continued every alternate day.Progesterone gel was added post-ET. In the mAC-FET cohort-17β transdermal estradiol gel(0.06%) 3mg/day was started from day3-5,rest of the protocol was similar. Statistical analysis was performed using appropriate non-parametric tests.Pearson coefficient(r) was used to assess linear-relationship.Two-tailed P<.05 indicated statistical significance. Main results and the role of chance Mean age and BMI of the patients with mAC-FET was 33.3±4.7 years and 24.4±3.7 kg/ m2 which was comparable across all groups (P=.14,P=.52 respectively). Clinical pregnancy rate in the mAC-FET group was 52.94%(18/34). 3 patients had an early abortion. Baseline relaxin-2 levels, median[Interquartile range(IQR)] were comparable- AC-FET cohort-9.1pg/mL(8.6-16.8), mAC-FET cohort-11.5pg/mL(9.6-13.7) and the infertility cohort-10.9pg/mL(8.4-14.5) (P=0.74) The primary outcome was the comparable levels of serum relaxin-2, in early pregnancy in the mAC-FET group and spontaneous conception group - median (IQR) 449.8pg/mL(73.1-492.3) and 487.9pg/mL(419.1-497.8) respectively (P=.12) The relaxin-2 levels, in early pregnancy in the mAC-FET group were significantly higher than the AC-FET group median(IQR) 449.8pg/mL(73.1-492.3) and 7.9pg/mL(7.8-9.5) respectively (P=.0005). As secondary outcomes, we studied the late luteal rise of relaxin-2 in the mAC-FET group and the relationship of late luteal progesterone with relaxin-2 in early pregnancies in the mAC-FET cohort. A late luteal rise of relaxin-2 was not demonstrated in the mAC-FET cohort. The serum relaxin-2, on the day of start of progesterone and on day5-9 post ET- median(IQR) 11.5pg/mL(9.6-13.7) and 11.4pg/mL(9.0-18.5), respectively was comparable (P=.18). The relationship between serum relaxin-2 in early pregnancy and the progesterone levels on day5-9 post ET in the mAC-FET cohort was not significant r = -.059 (P=.07) Limitations, reasons for caution This was a small proof- of-concept single centre study. Due to the limited numbers and short duration of the study, we could not compare efficacy, cancellation rates and pregnancy outcomes of the mAC-FET protocol with other FET protocols. Wider implications of the findings The mAC-FET protocol studied for endometrial preparation was similar to the AC -FET protocol regarding monitoring,flexibility and consistent progesterone exposure with the added advantage of the presence of the CL.This may decrease the risk of maternal/neonatal complications. Larger studies are needed to confirm it’s efficacy and impact on pregnancy outcomes. Trial registration number Not Applicable