Ovulation side and cycle fecundity: a retrospective analysis of frozen/thawed embryo transfer cycles

The aim of the study was to evaluate a possible lateral difference in ovari an activity and its effect on cycle fecundity, A database was analysed retr ospectively which covered 477 cycles in which frozen/thawed embryo transfer had been carried out. The cycles were spontaneous, with no hormonal treatm ent. Women with ovulation problems as a reason for infertility treatment we re excluded. Factors investigated were the side of ovulation, endometrial t hickness on cycle days 10-12 and on the day of embryo transfer, and pregnan cy rate per embryo transfer. Ovulation was right-sided in 273 of the 477 cy cles (57.2%) and left-sided in 204 of the cycles (42.8%) (95% CI 38.3-47.2, P = 0.002), In the age category of 30-37 years, covering 288 cycles, the i ncidence of left-sided ovulation was 126 (43.7%, 95% CI 38.0-49.5, P = 0.03 4), In this category, the endometrial thickness (+/-SD) was significantly g reater on the day of embryo transfer (i.e, at time of implantation) when th ere had been left-sided ovulation compared with right-sided [9.6 mm (2.0) v ersus 9.1 mm (1.8), P = 0.037], In addition, the pregnancy rate per embryo transfer was higher when ovulation had been on the left side [32/126 (25.2% ) versus right side 24/162 (14.8%), P = 0.035, 95% CT 0.0122-0.199], In con clusion, right-sided ovulation was more frequent than left-sided in the who le group, This is the first study to report that the side of ovulation has a clinical impact. These data support the hypothesis that the side of ovula tion is significant in terms of embryo implantation.