Table 1 Demographic and clinical data of the index stimulated IVF/ICSI cycle and FET cycle

 Age at index IVF/ICSI (years)

31.4 ± 4.8

31.7 ± 4.7

 Duration of subfertility (years)

4.5 ± 3.2

4.4 ± 3.1

 Body mass index (kg/m²)

21.4 ± 2.9

21.5 ± 3.1

 Primary subfertility

169/364 (46.4%)

141/337 (41.8%)

Number of previous ET cycles

1 (0–1)

0 (0–1)

Tubal

123/364 (33.8%)

111/337 (32.9%)

 Uterine

5/364 (1.4%)

4/337 (1.2%)

 Anovulation

8/364 (2.2%)

14/337 (4.2%)

 Diminished ovarian reserve

8/364 (2.2%)

7/337 (2.1%)

 Mixed factors of female

70/364 (19.2%)

77/337 (22.8%)

 Male

36/364 (9.9%)

30/337 (8.9%)

 Both husband and wife

109/364 (29.9%)

86/337 (25.5%)

 Unexplained

5/364 (1.4%)

8/337 (2.4%)

Number of oocytes retrieved

14.5 ± 7.9

15.6 ± 8.5

Number of mature oocytes

12.5 ± 7.0

13.4 ± 7.3

 Maternal age at FET (years)

32.2 ± 5.2

32.5 ± 4.6

 First ET cycle

191/364 (52.5%)

178/337 (52.8%)

 Endometrial thickness (mm)

9.8 ± 2.0

9.8 ± 1.6

 Duration of estradiol administration (days)

14.2 ± 2.9

14.5 ± 2.9

 P levels (ng/mL) ^*

0.5 ± 0.2

0.4 ± 0.2

 E₂ levels (pg/mL)

253.3 (175.7–400.7)

253.6 (179.5–544.2)

 Number of embryos transferred

2 (2–2)

2 (2–2)

 Number of good-quality embryos

2 (1–2)

2 (1–2)

 Single embryo FET cycles

50/364 (13.7%)

50/337 (14.8%)

 Single cleavage-stage embryo

18/272 (6.6%)

18/252 (7.1%)

 Single blastocyst

32/83 (38.6%)

32/81 (39.5%)

 Cleavage stage

272/364 (74.7%)

252/337 (74.8%)

 Blastocyst stage

83/364 (22.8%)

81/337 (24.0%)

 Both stage

9/364 (2.5%)

4/337 (1.2%)