LAUSR

Do serum progesterone levels differ among POSEIDON groups undergoing a modified natural cycle (mNC)? Serum progesterone levels in a mNC do not differ significantly across different POSEIDON groups. In a mNC, the aim is to mimic a natural ovulatory cycle with minimal intervention in preparation for a frozen embryo transfer (FET). Adequate progesterone production by the corpus luteum is essential to prepare the endometrium for embryo implantation. In women with advanced maternal age and poor ovarian reserve, particularly those in POSEIDON group 4, hormonal dysfunction in the early follicular phase can impair follicular development, which may contribute to luteal phase deficiency and insufficient progesterone production. This retrospective cohort analysis included infertile patients undergoing a single euploid embryo transfer (SEET) with a mNC, from January 2018 to December 2024. Ovulation was triggered with Ovidrel 250 mg (Merk) followed by the administration of vaginal progesterone (Crinone 8%, Merk) twice a day. Patients ≤43 years were segregated according to their POSEIDON group as followed: Group 1 (n = 28): age <35, antral follicle count (AFC) ≥5, antimullerian hormone (AMH) >1.2, Group 2 (n = 28): age ≥35, AFC ≥5, AMF ≥1.2, Group 3 (n = 27): age <35, AFC <5, AMH <1.2ng/ml, Group 4 (n = 27): age ≥35, AFC <5, AMH <1.2. Serum progesterone levels were measured 1 day prior to the SEET and 2 and 10 days after the procedure. A total of 110 patients were included. The mean age for group 1: 30±1.2, AFC 20.2± 5.3, AMH: 5.1± 2.32 ng/ml. Group 2: 37.6±4.2 years, AFC 14.2± 3.4, AMH: 3.1± 1.32 ng/ml. Group 3: 33.5±1.1 years, AFC 4.2± 0.4, AMH: 0.78± 0.22 ng/ml. Group 4: 38.1± 4.4 years, AFC 4± 0.2, AMH: 0.51± 0.13 ng/ml. Serum progesterone levels 1 day before SEET were similar (Group 1: 23.4±2.2 ng/ml, Group 2: 27.4±1.5 ng/ml, Group 3: 21.7±2.5 ng/ml, Group 4: 26.3±1.3 ng/ml, p = 0.87). When evaluating serum progesterone levels 2 days after SEET no differences were found (Group 1: 25.5±1.8 ng/ml, Group 2: 23.4±1.6 ng/ml, Group 3: 28.1±1.5 ng/ml, Group 4: 23.1±1.2 ng/ml, p = 0.65). Similarly, ten days after SEET, progesterone levels showed no statistical differences between groups (Group 1: 28.1±2.3 ng/ml, Group 2: 26.43±2.5 ng/ml, Group 3: 27.1±1.5 ng/ml, Group 4: 24.3±2.3 ng/ml, p = 0.54). Only 8.1% (9/110) of patients required additional progesterone supplementation two days after SEET due to serum levels falling below 12 ng/ml. When categorized by POSEIDON groups, two patients were from Group 1 (22.22%, 2/9), three from Group 2 (33.34%, 3/9), three from Group 3 (33.34%, 3/9), and one from Group 4 (11.1%, 1/9), with no significant difference observed (p = 0.76). The retrospective nature of the study, small sample size and potential variability in the study center’s laboratory protocol(s) compared to other reproductive treatment centers may limit the external validity of our findings. The study’s findings suggest that serum progesterone levels during a mNC do not vary significantly across POSEIDON groups, even in women with advanced maternal age and poor ovarian reserve. This implies that progesterone supplementation may be required consistently across groups, highlighting the importance of luteal phase support in SEET cycles. No