Background: it is important to study a history of the science to appreciate the past as a motive for hard work in the present for better future. In the other hand, the factors affecting pregnancy rate of frozen embryos are yet to be clarified at different embryonic developmental stages. Objectives: to record a brief history of embryo cryopreservation in Iraq and to study many clinical and embryological factors that might affect the pregnancy rate. Subjects, materials and Method: a cross-sectional study of many clinical and em-bryological variable, where120 frozen-thawed embryo transfer cycles enrolled in the study at the period from January 2017 till July 2018. The variables were sta-tistically analyzed first by one factor analysis comparing between pregnant and non-pregnant cases; then by multivariate logistic regression analysis to illustrate main factors without a possible confounder effect. Results: In one factor analysis, the following variables showed a significantly high effect on pregnancy rate (P value <0.001) which are women’s age, women’s weight, number of retrieved oocytes, mature oocytes and good quality embryos, developmental stage, E2 level, and endometrial thickness. While in multivariate logistic regression analysis the women’s weight, the number of retrieved oocytes and good quality embryos were the main factors. Conclusions: it is judiciously to consider these factors while managing infertile couples with embryo cryopreservation programs especially the modifiable fac-tors.