Table 2 Oocyte characteristics and ART outcomes in women receiving donor oocytes frozen by slow-freezing or vitrification

Oocyte age (years), mean ± SD; range

25.1 ± 2.7; 20–31

26.0 ± 2.8; 21–31

0.08

Total number of cycles started

40

94

Total number of oocytes warmed/thawed

312

694

Oocytes warmed/thawed per cycle, mean ± SD

7.8 ± 2.8

7.4 ± 2.5

0.40

Oocyte survival rate,^b mean ± SD

72.3% ± 28.3%

86.0% ± 19.4%

< 0.01

2PN oocytes, mean ± SD

4.0 ± 1.7

5.2 ± 1.8

< 0.01

Embryo transfers,^c n (% of cycles)

37 (92.5)

91 (96.8)

0.36

 Transfers on Day 3,^d n (% of transfers)

31 (83.8)

19 (20.9)

< 0.01

 Transfers on Day 5/6,^d n (% of transfers)

0 (0.0)

68 (74.7)

 Transfers on unknown/other days,^d n (% of transfers)

6 (16.2)

4 (4.4)

Embryos transferred per cycle, mean ± SD

2.9 ± 1.0

2.1 ± 0.6

< 0.01

 Day 3 transfer,^d mean ± SD

2.7 ± 1.0

2.7 ± 0.7

0.99

 Day 5/6 transfer,^d mean ± SD

0

2.0 ± 0.4

< 0.01

 Transfer on unknown/other days,^d mean ± SD

3.5 ± 0.8

2.3 ± 0.5

0.03

Embryo cryopreservations, n (% of cycles)

4 (10.0)

50 (53.2)

< 0.01

Embryos cryopreserved, mean ± SD

1.8 ± 0.5

2.3 ± 1.1

0.34

Implantation rate,^e mean ± SD

14.4% ± 23.9%

50.4% ± 45.8%

< 0.01

 Day 3 transfer, mean ± SD

16.3% ± 25.4%

12.3% ± 22.1%

0.57

 Day 5/6 transfer, mean ± SD

0

61.0% ± 45.7%

Not done

 Transfer on unknown/other days,^d mean ± SD

4.2% ± 10.2%

50.0% ± 40.8%

0.19

Clinical pregnancies, n (% of transfers)

12 (32.4)

57 (62.6)

< 0.01

 Day 3 transfer,^d n (% of transfers)

11 (35.5)

5 (26.3)

0.72

 Day 5/6 transfer,^d n (% of transfers)

0

49 (72.1)

Not done

 Transfer on unknown/other days,^d n (% of transfers)

1 (16.7)

3 (75.0)

0.24

Number of oocytes needed for a pregnancy^f

17.3

7.5

< 0.01

Live birth deliveries, n (% of cycles)^g

10 (25.0)

49 (52.1)

< 0.01

Number of oocytes needed for a live birth^h

22.3

9.3

< 0.01

Oocyte efficiency, number of live births (% of warmed/thawed oocytes)ⁱ

14 (4.5)

75 (10.8)

< 0.01