Cumulative live birth rate after IVF: trend over time and the impact of blastocyst culture and vitrification.

While it has been shown that live birth rate per embryo transfer is higher for fresh blastocyst than for fresh cleavage stage embryo transfer, cumulative live birth rate (CLBR) per oocyte aspiration, including one fresh ET and all subsequent frozen embryo transfers (FET), does not seem to differ between the two culture strategies. 

A retrospective national register study including all oocyte aspirations performed in Sweden from 2007 to 2017 (n = 124 700 complete IVF treatment cycles) was carried out. The CLBR per oocyte aspiration increased significantly during the study period, from 27.0% to 36.3% (odds ratio (OR) 1.039, 95% CI 1.035-1.043) and from 30.0% to 43.3% if at least one FET was performed. 

The results suggest that blastocyst transfer, particularly when used in FET cycles and in combination with vitrification, is an important contributor to improved live birth rates over time. This gives a possibility for a lower number of oocyte aspirations needed to achieve a live birth and a shortened time to live birth.