Table 3 Univariate correlation between female demographics, follicular phase characteristics, and serum P₄ levels one day prior to warmed blastocyst transfer (FET-1)

Age, years

-0.078

0.30

Body mass index, kg/m²

-0.378

< 0.001

Antral follicle count, n

0.032

0.67

Follicular phase length, days

0.079

0.31

Follicle diameter one day prior to ovulation, mm

0.235

0.002

AUC-E₂ level, pg/mL

0.406

< 0.001

Peak E₂ level, pg/mL

0.480

< 0.001

AUC-LH level, IU/L

0.072

0.36

Peak LH level, IU/L

-0.006

0.94

Follicular phase AUC-P₄ level, ng/mL

0.286

< 0.001

Follicular phase peak P₄ level, ng/mL

0.351

< 0.001

Endometrial thickness one day prior to ovulation, mm ^b

-0.07

0.33

Luteinized unruptured follicle ^c

-0.236

0.002