Table 1 Basic characteristics of the 24 studies included in the review

Velde et al. (1998 [21])

PS

60

GnRHa

NM

O

36

1–6

0–4

1–6

Three groups: ①OPU-DN: 1–2 h, DN-ICSI: 0 h or 4 h; ②OPU-DN: 1–2 h and DN-ICSI: 0 h or OPU-DN: 5–6 h and DN-ICSI: 0 h; ③OPU-DN: 1–2 h and DN-ICSI: 4 h or OPU-DN: 5–6 h and DN-ICSI: 0 h

Yanagida et al. (1998) [22]

PS

544

GnRHa

NM

O

> 35

1–11

0

1–11

Grouped by OPU-DN: 1–3 h; 3–5 h; 5–7 h; 7–9 h; 9–11 h

Rienzi et al. (1998) [23]

RS

95

GnRHa

20%

O

36

2–12

0

2–12

Grouped by OPU-DN: ≤3 h; 3–6 h; 6–9 h; 9–12 h

Andrews et al. (2001) [24]

RS

1210

GnRHa

NM

O

36

0–1

Some time

0–5

Grouped by OPU-ICSI: < 3 h; 3–5 h; > 5 h

Hassan et al. (2001) [2]

PS

141

GnRHa

20%

O

NM

0–4

0–4

0–4

Three groups: ①OPU-DN: 0 h and DN-ICSI: 0 h; ②OPU-DN: 4 h and DN-ICSI: 0 h; ③OPU-DN: 0 h and DN-ICSI: 4 h

Jacobs et al. (2001) [25]

RS

432

GnRHa

20%

O

36

> 0–4

0

> 0–4

Grouped by OPU-DN: 0–2 h; 2–3 h; 3–4 h; > 4 h

Ho et al. (2003) [26]

RS

64

GnRHa

NM

O

34

1–8

0

1–8

Grouped by OPU-DN: < 2.5 h; 2.5–3.5 h; 3.5–4.5; 4.5–5.5; ≥5.5 h

Isiklar et al. (2004) [15]

PS

1260

GnRHa

5%

O

36

0–4

0

0–4

Grouped by OPU-DN: 0 h; 2–4 h

Falcone et al. (2008) [3]

RS

135

GnRHa

20%

O

> 36

2

0–10

2–12

Grouped by DN-ICS: 2–4 h; 4–5 h; 5–6 h; 6–7 h; 7–8 h; 9–12 h

Boldi et al. (2010) [27]

RS Ab

203

NM

NM

O

NM

NM

0–3

NM

Grouped by DN-ICS: 0 h; 1–3 h

Aletebi (2011) [4]

PS

309

GnRHant

NM

O

36

0–2

0–2

0–4

Three groups: ①OPU-DN: 0 h and DN-ICSI: 0 h; ②OPU-DN: 1 h and DN-ICSI: 1 h; ③OPU-DN: 2 h and DN-ICSI: 2 h

Patrat et al. (2012) [17]

RS

110

GnRHa

20%

O

36.5 ± 1

0–3

0–3

0–6

Grouped by OPU-DN OR DN-ICSI: 0.5 h as an interval

Esbert et al. (2013) [28]

RS Ab

1212

NM

NM

O

NM

2 or 4

NM

Within 4.5

Grouped by OPU-DN: 2 h; 4 h

Garor et al. (2015) [5]

RS

614

GnRHa/GnRHant

NM

O

34–38

0.08–7

0.08–5.2

NM

Grouped by OPU-DN: < 2 h; > 2 h

Grouped by DN-ICSI: < 1 h; > 1 h

Terasawa et al. (2016) [29]

RS Ab

302

MS/NC

NM

O

NM

> 0–3

NM

NM

Grouped by OPU-DN:< 2 h; 2–3 h; > 3 h

Ishikawa et al. (2016) [30]

PS Ab

54

NM

NM

O

NM

0–2

NM

NM

Grouped by OPU-DN: 0 h; 2 h

Pereira et al. (2016) [31]

RS

15

GnRHa/GnRHant

NM

O

35–37

1.9 vs 2.9

NM

NM

OPU-DN was compared between two groups with first complete fertilisation failure and next successful fertilisation in the same patient

Bárcena et al. (2016) [19]

RS

3178

GnRHa/GnRHant

20%

A

Mostly 36

0.5–3

0.6–10.8

1.4–11.7

Ten groups: grouped by OPU-DN OR DN-ICSI: by deciles

Pujol et al. (2018) [20]

RS

1468

GnRHa/GnRHant

20%

A

36

0.4–2.12

0.26–11.19

1.0–12.6

Ten groups: grouped by OPU-DN OR DN-ICSI: by deciles

Mizuno et al. (2018) [16]

PS

54

GnRHa/GnRHant

NM

O

36–38

0 or 2 h

2.5–4

2.5–4.5

Grouped by OPU-DN: 0 h; 2 h

Naji et al. (2018) [32]

RS

2051

GnRHa/GnRHant

5%

A

36

0–5

NM

NM

Grouped by OPU-DN:< 2 h; 2–5 h

Subgroup analysis: OPU-DN: 0 h; 0.5–2 h

Zhang et al. (2020) [33]

RS

3602

GnRHa/GnRHant

NM

O

> 36

2.2 ± 0.8

2.8 ± 1

NM

Grouped by DN –ICSI: 0–1 h; 1–2 h; 2–3 h; 3 h–4 h; 4–5 h; > 5 h

Azizi et al. (2020) [34]

PS

613

GnRHa/GnRHant

NM

O

35–39

0.5–6

0–4.8

NM

Grouped by OPU-DN: < 2 h; > 2 h

Grouped by DN-ICSI: < 2 h; > 2 h

Maggiulli al. (2020) [35]

RS

1444

GnRHa/GnRHant

5%

A

34–37

2–7

0

2–7

The relationship between blastocyst formation rate and IO-DN was analysed