The true natural cycle frozen embryo transfer - impact of patient and follicular phase characteristics on serum progesterone levels one day prior to warmed blastocyst transfer

Table 1 Patient demographics at baseline, embryological data, and true natural cycle characteristics

Age, years	36 (32–40)
Body mass index, kg/m²	23.1 (21.1–25.9)
Antral follicle count on Day 2/3, n	14 (9–18)
Cause of infertility, n (%)
Unexplained infertility	57 (32.0)
Male factor	54 (30.3)
Advanced maternal age and/or diminished ovarian reserve	48 (27.0)
Tubal factor	6 (3.4)
Endometriosis	6 (3.4)
Monogenic disorders	7 (3.9)
Duration of infertility, months	28 (15.75–48.0)
Number of previous IVF cycles, median (minimum-maximum)	0 (0–8)
Previous childbirth, n (%)	35 (19.7)
Day of vitrification, n (%)
Day 5	118 (66.3)
Day 6	60 (33.7)
Blastocyst morphology^a, n (%)
Excellent	20/165 (12.1)
Good	74/165 (44.9)
Average	66/165 (40.0)
Poor	5/165 (3.0)
Number of patients with PGT-A, n (%)	57 (32.0)
Number of patients with PGT-M, n (%)	7 (3.9)
Number of blastocyt(s) transferred	1 (1–2)
Number of cycles with single blastocyst transfer, n (%)	130/165 (78.8)
Follicular phase length, day	13 (11–15)
Follicle diameter one day prior to ovulation, mm	19.2 (17.8–20.9)
Endometrial thickness one day prior to ovulation, mm	10.4 ± 2.0
Number of patients with follicular collapse, n (%)	153 (86)
Number of patients with luteinized unruptured follicle ^b, n (%)	25 (14)

Values are given as mean ± SD, median (25th – 75th percentiles), or n (%)
IVF: in-vitro fertilization, PGT-A: preimplantation genetic testing for aneuploidy, PGT-M: preimplantation genetic testing for monogenic disorders
^a Blastocyst grading was categorized as excellent (3AA, 4AA, 5AA), good (3,4,5,6 AB or BA), average (3,4,5,6 BB or AC or CA), and poor (3,4,5,6 BC or CC). When more than one embryo was transferred, the one with the best morphological grading was included in the analysis
^b Luteinized unruptured follicle (LUF) was diagnosed when there was no follicular collapse despite an LH surge (> 17 IU/L) and increased serum P₄ (> 1.5 ng/mL)

ISSN: 1477-7827