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Pregnancy rate fluctuations during routine work in an assisted reproduction technology unit.

BACKGROUND
Fluctuations in spontaneous pregnancy rates have been observed in the general population. The purpose of this study was to evaluate whether pregnancy rates fluctuate over time in a homogeneous assisted reproduction treatment unit.


METHODS
The study sample consisted of 3522 consecutive assisted reproduction cycles conducted from January 1996 to December 1999. Only fresh cycles in women <41 years old were included. All pertinent clinical data were prospectively collected on a computerized database and analysed at the end of the study.


RESULTS
Throughout the 4 years of the study, monthly pregnancy rates fluctuated between 10.5 and 34.1% (mean 21.4%) per cycle, and between 13.6 and 41% (mean 27.26%) per transfer. These fluctuations did not follow any specific seasonal pattern.


CONCLUSION
During routine work in an assisted reproduction treatment unit, there are random fluctuations in the pregnancy rate. This factor should be considered in studies performed in a specific time-period.