Background: The transfer of multiple embryos during ART procedures (IVF/ICSI) in order to maximize the chance of pregnancy, has resulted in increasing rates of multiple pregnancies with a 20- fold increased risk of twins and 400- fold increased risk of higher order pregnancies with significantly high maternal and perinatal morbidity and mortality in comparison with singleton. Since at present there is no limitation in number of embryos being transferred in ART cycles in infertility centers in Iran, in order to evaluate the relationship between number of embryos transferred, pregnancy rates and multiple pregnancy, this study was performed in a referral university center.

Methods: In a cross sectional descriptive analytical study a total of 536 ART cycles in infertile patients treated at the Infertility Department of Vali-e-Asr Hospital & Vali-e-Asr Reproductive Health Research Center from October 1999- March 2003 were evaluated using a questionnaire dealing with the parameters affecting ART outcome.
Results: There was a total pregnancy rate of 21% with a multiple pregnancy rate of 12%. Increased age had a negative effect on pregnancy rate with a significant difference over 40 years (p<0.05). Pregnancy rate was higher with increased number of transferred embryos but it was only statistically significant when three versus two embryos were transferred (p<0.008). When more than three embryos transferred, although there was an increase in pregnancy rate, the difference was not statistically significant, but there was a significant increase in multiple pregnancy rate.
Conclusions: The maximum number of transferred embryos in ART cycles should not precede three embryos especially in age groups less than 40 and also when good quality embryos are available.

Keywords: Pregnancy rate, multiple pregnancy rate, transferred embryos, ART cycles

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