Table 1.
Characteristics of studies included in the meta-analysis
| Study | Area/duration | Type of study | Population | Embryo transferred | Freezing techniques | FET protocol | Measurements assessed | ||
|---|---|---|---|---|---|---|---|---|---|
| Fresh ET | FET | ||||||||
| 1994 | Wada | UK 1985–1991 |
Retro | IVF vs. FET | D2/D3 embryos | Cleavage embryos/blastocysts | Slow freezing | Natural/HRT cycles | Preterm birth LBW Still birth |
| 2005 | Wang | Australia 1996–2000 |
Retro | IVF/ICSI/GIFT vs. FET | Not mentioned | Not mentioned | Not mentioned | Not mentioned | Preterm birth LBW |
| 2008 | Belva | Belgium 1983–2006 |
Retro | IVF/ICSI vs. FET | D1,2,3,5 embryo | D1/2/3/5 embryo | A slow controlled-rate freezing procedure | Natural cycles/stimulated cycles | Preterm birth LBW |
| 2008 | Shih | Australia 1978–2005 |
Retro | IVF/ICSI/GIFT vs. FET | D2/D3 embryo | D2/D3 embryo | No specific description | Natural/artificial cycles | Preterm birth LBW Perinatal mortality Cesarean section |
| 2010 | Aflatoonian | Iran 2006–2008 |
Retro | IVF/ICSI vs. FET | D2/D3 embryo | D2/D3 embryo | Vitrification | Artificial cycles | Preterm birth LBW |
| 2010 | Pelkonen | Finland 1995–2006 |
Cohort study | IVF/ICSI vs. FET | D2/D3 embryo | D2/D3 embryo | Slow freezing | Natural/artificial cycles | Preterm birth LBW Still birth Perinatal mortality Cesarean section |
| 2010 | Pinborg | Denmark 1995–2007 |
Cohort study | IVF/ICSI vs. FET | D2/D3 embryo | D2/D3 embryo | Slow freezing | Not mentioned | Preterm birth LBW Still birth Perinatal mortality Cesarean section |
| 2010 | Wikland | Sweden 2006–2008 |
Cohort study | IVF/ICSI vs. FET | blastocysts | D2/D3 embryo/blastocysts | Vitrification/slow-freezing | Natural/artificial/stimulated cycles | Preterm birth LBW Perinatal mortality Cesarean section |
| 2011 | Henningsen | Denmark 1994–2006 |
Cohort study | IVF/ICSI vs. FET | D2 embryo | D2 embryo | Slow-freezing | Not mentioned | LBW |
| 2012 | Kalra | United States 2004–2006 |
Cohort study | IVF vs. FET | Not mentioned | Not mentioned | Not mentioned | Not mentioned | Preterm birth LBW |
| 2012 | Kato | Tokyo 2006–2008 |
Retro | IVF/ICSI vs. FET | Cleavage stage embryo/blastocyst | Cleavage stage embryo/ blastocyst | Vitrification | Natural/artificial cycles | Preterm birth LBW Still birth Perinatal mortality |
| 2013 | Wennerholm | Denmark −2007 |
Retro | IVF/ICSI vs. FET | D2 embryo | D2 embryo | Slow-freezing | Not mentioned | Preterm birth LBW Still birth Perinatal mortality Cesarean section |
| 2015 | Kemal | Antalya 2012–2012 |
Retro | IVF vs. FET | Blastocyst | Blastocyst | Vitrification | Artificial cycles | Still birth |
Abbreviation: Retro retrospective