Background. The aim of this study was to analyse the results of natural IVF/ICSI cycles and to find out which factors have an impact on the success of the cycle.

Methods. 340 natural IVF/ICSI cycles in 162 infertile couples were analysed within a retrospective study. Cycles were divided in groups according to the cause of infertility and women’s age and pregnancy rates were compared. A t-test was used to obtain the different values of the variables between the cycles with pregnancies and cycles without pregnancies.

Results. A premature ovulation occurred in 32 cases (9.41%), an oocyte was obtained in 244 cycles (79.2%), fertilization occurred in 175 cases (71.72%) and pregnancy in 41 cycles (the pregnancy rate per puncture = 13.31, per transfer = 25.31). The highest pregnancy rate per puncture was achieved in patients with idiopathic infertility (17.91) followed by male infertility with ICSI procedure (12.67) and female infertility (11.40%). Pregnancy rate per cycle was 13.42 in women below the age of 38 years, 8.11 in women between 38 and 40 years, and no pregnancy were achieved in women 40 and over years of age. There are statistically significant higher values of estradiol measured on the day of the HCG injection and later application of HCG in cycles that resulted in pregnancy than those which did not result in a pregnancy. There were no differences in the duration of infertility, the patients’ age, the average and maximum diameter of the follicle and the thickness of the endometrium on the day of the HCG injection as well as between the basal values of FSH and LH between the two groups.

Conclusions. Satisfactory results are obtained with the natural IVF/ICSI cycles independent from the cause of infertility. A higher pregnancy rate per puncture is expected with higher levels of estradiol, a later application of HCG and in women below the age of 38 years.