Table 1.

Baseline characteristics.

Characteristics	Natural cycles (n = 513)	HRT cycles (n = 287)	P-value
Age (years)	28.74 ± 2.89	29.08 ± 3.01	0.117
Body-mass index (kg/m)	22.32 ± 3.07	22.52 ± 3.30	0.379
Duration of infertility (years)	3.26 ± 2.11	3.29 ± 2.35	0.846
Previous conception n (%)	219/513 (42.69)	133/287 (46.34)	0.318
Indications for IVF			0.364
Tubal factor	276/513 (53.80)	156/287 (54.36)
Male factor	113/513 (22.03)	64/287 (22.30)
Unexplained infertility	20/513 (3.90)	18/287 (6.27)
Combined factors	104/513 (20.27)	49/287 (17.07)
Antral follicle count in both ovaries	16.46 ± 5.46	16.87 ± 5.99	0.339
Baseline sex hormone
FSH (IU/L)	6.34 ± 1.50	6.32 ± 1.46	0.812
LH (IU/L)	4.78 ± 1.93	4.83 ± 2.21	0.717
Oestradiol (pg/mL)	37.07 ± 14.60	37.94 ± 15.64	0.430
Total testosterone (ng/dL)	28.46 ± 14.03	35.96 ± 17.82	<0.001
Fresh cycle variables
Days of ovarian stimulation	9.28 ± 1.40	9.49 ± 1.68	0.056
Total gonadotropin dose (IU)	1559.32 ± 479.52	1634.78 ± 500.26	0.036
Oestradial level on HCG trigger day (pmol/L)	3431.55 ± 1810.08	3758.37 ± 1801.59	0.020
Progesterone level on HCG trigger day (nmol/L)	1.14 ± 0.52	1.26 ± 0.58	0.006
Endometrial thickness on HCG trigger day (cm)	1.07 ± 0.20	1.06 ± 0.20	0.512
No. of oocytes retrieved	14.29 ± 5.74	14.69 ± 5.68	0.339
No. of 2PN embryos	9.43 ± 3.97	10.17 ± 4.53	0.015
No. of cleavage embryos	9.29 ± 3.96	9.94 ± 4.36	0.032
Fertilization method			0.333
IVF n (%)	359/513 (69.98)	210/287 (73.17)
ICSI n (%)	127/513 (24.76)	68/287 (23.69)
IVF +ICSI n (%)	27/513 (5.26)	9/287 (3.14)
No. of day-3 embryos suitable for transfer	6.96 ± 2.99	7.59 ± 3.69	0.015
OHSS n (%)	3/513 (0.58)	4/287 (1.39)	0.258
FET cycle variables
Endometrial thickness before transfer (cm)	1.00 ± 0.17	0.94 ± 0.16	<0.001
Timing of embryo transfer—no./total no. (%)			0.853
Day 5	465/513 (90.64)	259/287 (90.24)
Day 6	48/513 (9.36)	28/287 (9.76)
No. of remaining frozen blastocysts	4.19 ± 2.90	4.27 ± 3.00	0.720