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 2 The daily endocrine and ultrasonographic monitoring data as categorized according to the day of ovulation

	Ovulation − 3 days n = 132	Ovulation − 2 days n = 166	Ovulation − 1 day n = 178	Ovulation + 4 days (FET − 1 day) n = 178
LH level, IU/L	9.8 (8.2–13.1)	19.4 (13.9–26.2)	41.3 (30.1–56.0)	NA
E₂ level, pg/mL	223.0 (168.5–272.5)	301.0 (236.0–364.5)	235.0 (170.8–298.5)	NA
P₄ level, ng/mL	0.5 (0.3–0.7)	0.6 (0.4–0.9)	1.0 (0.8–1.2)	12.9 (9.3–17.2)
Follicle diameter, mm	16.3 (15.2–17.7)	18.0 (16.8–19.5)	19.2 (17.8–20.9)	NA

Data are presented as median (25th – 75th percentiles). LH, luteinizing hormone; E₂, estradiol; P₄, progesterone; FET, frozen embryo transfer; NA, not available

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