2024년 미국불임학회(ASRM) P-156 When confirmation of ovulation date is unclear during natural cycle frozen embryo transfer, should it be thawed the day before or the next day? (자연주기 동결배아 이식 시 배란일 확인이 불분명한 경우, 전날에 해동해야 하나요, 아니면 다음 날 해동해야 하나요?)

G.W. Kim¹, S.G. Kim¹, H.J. Son¹, M.J. Kim¹, G.D. Heo¹, H.Y. Kim¹, Y.W. Kim¹, J.Y. Seong¹, H.K. Noh¹, K.H. Lee¹.
¹Mamapapa&baby Ob/Gy Clinic, Baby dream research center, Ulsan, Korea- South.

Objective

Spontaneous ovulation during the natural menstrual cycle is a simple and efficient method for synchronization between frozen embryos and the endometrium. In practice, the natural frozen embryo transfer (FET) cycle can be advantageous in that the endometrial preparation is performed under the most physiological conditions. However, natural FET cycle can be cumbersome as it requires numerous monitoring visits to detect ovulation. Furthermore, this strategy lacks flexibility and does not allow for embryo transfer to be planned in advance, nor does it provide the possibility to avoid embryo transfer on weekends. In particular, the timing following one`s endogenous the luteinizing hormone (LH) surge may be less clear because the amplitude and duration of the LH surge varies considerably among women. They may not be able to routinely apply the endometrium and FET schedules of the spontaneous LH peak group due to lack of detailed information regarding LH peak criteria. The purpose of this study was to compare one-day early versus next-day thawing for FET in patients with less obvious spontaneous LH peaks.

Materials and Methods

We prospectively reviewed 1,341 FET cycles using a natural cycle protocol from October 2022 to December 2023. Ovulation timing was determined by vaginal ultrasound and hormone testing. For patients with confirmed LH peak, embryos were thawed and transplanted on the corresponding day based on the day of ovulation (n=1,207). However, patients with unclear spontaneous LH peak were divided into two groups for FET: one-day early thawing (n=64) and next-day thawing (n=70). We compared the FET results of the two groups.

Results

In each group, age, the number of transferred embryos and percentage of top quality embryos did not show significant differences. There were no significant differences between two groups in the clinical pregnancy rate [one-day early thawing: 56.3% (36/64) vs. next-day thawing: 62.9% (44/70), P=0.802] and spontaneous abortion rate [2.8% (1/36) vs. 2.3% (1/44), P=0.562].

Total pregnancy rate of FET cycles was 56.6% (746/1341). In addition, there was no statistical difference in the clinical pregnancy rate [56.3% (679/1207) vs. 59.7% (80/134), p=0.746] and spontaneous abortion rate [1.6% (11/679) vs. 2.5% (2/80), p=0.914] of patients with clearly identified LH peak compared to patients without clearly identified LH peak.

Conclusions

In patients with unclear identification of the spontaneous LH peak in the natural FET cycle, thawing the day before or the next day did not negatively affect pregnancy rates.

한글요약

자연주기 냉동 배아이식에서 배란일이 불확실한 경우, 배아 해동을 하루 전 또는 다음 날 하는 것이 임신율에 미치는 영향을 비교하였다. LH 피크가 명확하지 않아 배란일이 불확실한 환자군을 해동 시점에 따라 나눈 결과, 임신율과 유산율에 유의한 차이는 없었다. 따라서 LH 피크가 명확하지 않은 경우에도 해동 시점을 하루 앞당기거나 늦추는 것이 임신 결과에 부정적인 영향을 미치지 않으며, 환자 및 연구실 일정에 따라 유연하게 조정함으로써 업무 부담을 줄일 수 있을 것이다.