Retrospective cohort study.
Private fertility center.
This retrospective study included 2,150 blastocyst transfers, including all 1,460 fresh autologous blastocyst transfers and all 690 transfers of autologous blastocysts derived from post-thaw extended culture of thawed bipronuclear oocytes in the 8-year study period 2004-2011.
None.
Visualized EP and treated persistent pregnancy of unknown location.
The rate of visualized EP was 1.5 % in pregnancies in fresh autologous cycles, which was significantly more than the rate of 0 with autologous post-thaw extended culture. The rates of treated persistent pregnancy of unknown location were 2.5 % and 0.3 % in these two groups, respectively, a difference that was also statistically significant (relative risk 7.3, 95 % confidence interval 1.7-31.0).
Relative to fresh transfer, thawed ET was associated with significantly reduced incidence of EP. These findings are consistent with ovarian stimulation increasing the risk of EP.