Table II.
Embryo characteristics and outcomes after culture under either 5 or 20% oxygen, analysed by comparing averages per cycle by using linear regression analysis and by comparing the outcomes per oocyte/embryo by using GEE binary logistic models.
| 5% O 2 | 20% O 2 | P value | Adjusted P value 6 | |
|---|---|---|---|---|
| Analysis per cycle | n = 195 | n = 676 | ||
| Number of oocytes | 8.3 ± 5.1 | 8.1 ± 5.0 | NS | NS |
| Number of patients with >10 oocytes | 64 (32.8%) | 229 (33.9%) | NS | - |
| Number of patients with >20 oocytes | 7 (3.6%) | 25 (3.7%) | NS | - |
| Number of injected or inseminated oocytes | 7.4 ± 4.5 | 7.1 ± 4.5 | NS | NS |
| Fertilization rate1 | 62.4 ± 26.5 | 62.7 ± 26.7 | NS | NS |
| Cleavage rate2 | 97.0 ± 10.4 | 94.2 ± 16.2 | P < 0.05 | P < 0.05 |
| Good-quality embryo rate2,4 | 48.0 ± 33.8 | 30.4 ± 32.5 | P < 0.001 | P < 0.001 |
| Number of embryos transferred3 | 1.2 ± 0.4 | 1.3 ± 0.5 | P < 0.05 | P < 0.05 |
| Number of embryos cryopreserved3 | 2.1 ± 2.3 | 1.4 ± 2.0 | P < 0.001 | P < 0.001 |
| Embryo utilization rate2,5 | 76.1 ± 25.7 | 66.2 ± 31.6 | P < 0.001 | P < 0.001 |
| Number of thaw cycles with cryopreserved embryos | 1.10 ± 1.4 | 0.8 ± 1.2 | P = 0.002 | - |
| Analysis per oocyte/embryo | n = 1627 | n = 5448 | Crude GEE-OR [95% CI] | Adjusted GEE-OR [95% CI] 6 |
| Number of injected or inseminated oocytes | 1448/1627 (89.0%) | 4779/5448 (87.7%) | 1.1 [0.88–1.48] | 1.2 [0.90–1.49] |
| Normal fertilization rate (2PN) | 877/1448 (60.6%) | 3031/4779 (63.4%) | 0.9 [0.78–1.09] | 0.9 [0.79–1.10] |
| Cleavage rate | 849/877 (96.8%) | 2865/3031 (94.5%) | 1.8 [1.18–2.86] | 1.8 [1.17–2.85] |
| Good-quality embryo rate | 402/877 (45.8%) | 936/3031 (30.9%) | 2.0 [1.59–2.39] | 1.9 [1.59–2.39] |
| Embryos transferred | 226/877 (25.8%) | 842/3031 (27.8%) | 0.9 [0.76–1.05] | 0.9 [0.76–1.06] |
| Embryos cryopreserved | 404/877 (46.1%) | 900/3031 (29.7%) | 2.0 [1.66–2.47] | 2.0 [1.67–2.49] |
| Embryo utilization rate | 630/877 (71.8%) | 1742/3031 (57.5%) | 1.8 [1.50–2.20] | 1.8 [1.50–2.20] |
Data are presented as mean ± SD or as number (%).
1Expressed as the proportion of the number of injected or inseminated oocytes.
2Expressed as the proportion of the number of two pronuclei (2PN) zygotes per cycle.
3Expressed as mean per cycle with zygotes.
4Defined as having 2PN on Day 1 and four blastomeres on Day 2 with less than 20% fragmentation and no multinucleated blastomeres.
5Defined as the proportion of zygotes per cycle that is transferred or cryopreserved as an embryo.
6The difference between the oxygen groups was corrected for maternal age, cycle rank order, cause of subfertility and fertilization method, except at number of oocytes and number of injected or inseminated oocytes where fertilization method was left out of the analysis.
NS = not significant, P > 0.05.
GEE-OR = odds ratio derived from the general estimating equations (GEE) binary logistic models.