Results:

From November 2015 to December 2017, 2539 women underwent an IVF cycle with their own eggs. Of these cycles, 121 were abandoned before egg collection or had no eggs collected. On three occasions there was failure to obtain sperm. There were 78 cycles with complete failure to fertilise and two with failed cleavage. Mature oocyte cryopreservation was performed for 17 patients and there were 8 cycles where no eggs were suitable to inject following denudation for ICSI. There were 21 cases of freeze all embryo cycles and 11 where no embryo transfer was performed due to abnormal development. Three surrogacy cycles were excluded as were two cycles which were lost to follow up leading to no outcome information being available. We also excluded 15 cycles where both TLI and SC incubators were used. This resulted in a total of 2258 cycles included in this retrospective analysis, of which 1219 were in the TLI arm and 1039 in the SC arm (figure 1).
Table 1 outlines the baseline characteristics of the two groups for comparison. As reported previously 4, there was a bias to older patients in the TLI group where the mean age was 35.15 years as compared with 33.47 years in SC (MD, 1.68 years, 95% CI 1.31 to 2.05). Despite being older, the women in the TLI arm had more oocytes retrieved, with a mean of 12.15 oocytes vs 10.87 oocytes for SC (MD 1.28, 95% CI 0.74 to 1.82). Age and number of oocytes were therefore adjusted for when analysing the outcomes. The proportion of cycles that had a transfer performed was similar between the two groups, as was the mean number of embryos transferred. However the proportion of cycles with embryos available for cryopreservation (TLI 49.38 % vs SC 43.79%, OR 1.25, 95% CI 1.06 to 1.48, p = 0.008) as well as the mean number of embryos cryopreserved (TLI 1.37 ± 2.03 vs SC 1.10 ± 1.68, MD 0.08, 95% CI 0.10 to 0.41, p = 0.001) was higher in the TLI group. The embryo utilisation rate was also higher in the TLI group, but this did not reach statistical significance (TLI 37.08% vs SC 36.29%, OR 1.03, 95% CI 0.97 to 1.11, p = 0.323)
Table 2 outlines the clinical outcomes in the two groups. The clinical pregnancy rate per cycle was significantly higher in the TLI group (TLI 46.84% vs SC 41.87%, OR 1.22, 95% CI 1.04 to 1.45, p = 0.017). There was no significant difference in the multiple pregnancy rate (TLI 6.48% vs 4.83%, OR 1.37, 95% CI 0.79 to 2.37, p = 0.267). There was a significantly higher live birth rate per cycle in the TLI arm (TLI 39.87% vs SC 38.02%, OR 1.08, 95% CI 0.91 to 1.28, p = 0.039). After adjusting for the baseline characteristics of age and number of oocytes which had been noted to be significantly different between the TLI and SC groups, the live birth rate was still significantly higher in the TLI group (aOR 1.20, 95% CI 1.01 to 1.44, p = 0.040).
As noted above, a higher proportion of cycles in the TLI arm had embryos available for cryostorage which in turn translated to a non-significant increase in the proportion of women who had an embryo available in cryostorage following an unsuccessful fresh embryo transfer (TLI 41.80% vs SC 36.69%, OR 1.24, 95% CI 0.99 to 1.55, p = 0.058). This is turn led to a non-significant trend towards a higher number of frozen embryo transfers being performed in the TLI arm (TLI 1.25 ± 0.90 vs SC 1.22 ± 0.90, OR 0.03, 95% CI -0.12 to 0.19, p = 0.707). There was no significant difference in the live birth rate per frozen embryo transfer (TLI 30.96% vs SC 30.39%, OR 1.03, 95% CI 0.74 to 1.42, p = 0.377).
The cumulative live birth rate per cycle after taking into account both fresh and frozen embryo transfers from the study period was on initial analysis not significantly different between TLI and SC groups (TLI 50.29% vs SC 46.78%, OR 1.15, 95% CI 0.97 to 1.36, p = 0.125). However, upon adjusting for age and number of oocytes, the cumulative live birth rate was significantly higher in the TLI group (aOR 1.24, 95% CI 1.04 to 1.48, p = 0.016).