Objective: To find out whether: 1) the blastocysts transfer rises the successfulness of IVF and ET (G/ET) and 2) the 2-blastocyst transfer lowers the incidence of multiple pregnancies (IR). Design: Prospective study of 46 patients involved in a prolonged 5-day cultivation of IVF and ET programme. Setting: Centre for Assisted Reproduction, Clinic of Gynecology and Obstetrics, Teaching Hospital and Palacky University in Olomouc. Methods: Patients with at least 5 acquired embryos were included in the group. The cultivation in media commercially produced by Scandinavian IVF Science took 5 days. Results: In 91 % of patients in the observed group (n = 46) morulas or blastocysts were acquired. The IVF and ET success rate after 5-day cultivation and subsequent transfer of two embryos was 37 % pregnancies per a started cycle (G/cycle), 40 % pregnancies per an embryotransfer (G/ET) and the implantation rate (IR) was 31 %. Relatively high percentage of double pregnancies (53 %) is alarming. Following parameters were assessed: age, sterility cause, number of previous IVF cycles, stimulation scheme, E2 level on the day of hCG application, number of acquired oocytes and pronuclear stages, percentage of grown blastocysts, the quality of transferred embryos and endometrium thickness on the day of transfer. The only statistically significant difference was found in E2 level on the day of hCG application. Pregnant patients had lower levels of estradiol (average value 11.8 ± 4.8 nmol/l) compared to patients who did not become pregnant (18.6 ± 11.9 nmol/l). Conclusion: In selected groups of patients who refuse multiple pregnancies only one blastocyst should be transferred.

        Key words: IVF and ET, blastocyst transfer