Patterns of increase in serum estradiol in response to ovarian stimulation and their relationship to oocyte fertilization and cleavage in vitro

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Abstract
The in vitro fertilization and cleavage rates of oocytes obtained from patients exhibiting two different patterns of increase in serial serum concentrations of estradiol (E2) in response to ovarian stimulation were compared. Forty-two cycles (from 38 stimulated patients) were evaluated because they fulfilled requirements from two predefined patterns of E2 response to ovarian stimulation. In 16 cycles, serial serum E2 concentrations followed a “plateau” pattern (group A), viz., the rate of increase in the serum concentration of E2 decreased prior to the administration of human chorionic gonadotropin (hCG). In 26 cycles, serial serum E2 concentrations followed a “leap” pattern (group B), in which the rate of increase in serum concentrations of E2 increased progressively up to and including the day of hCG administration. There was no significant difference in the fertilization rate of oocytes obtained from patients exhibiting either pattern A or pattern B (78 versus 74%) but the cleavage rate was significantly higher in ova obtained from patients who exhibited pattern A rather than pattern B (72 vs 50%; P ⩽ 0.01). In addition, embryos resulting from fertilized ova obtained from women in group A were of better quality morphologically than those obtained from women in group B (mean embryo grades, 3.9 vs 3.2; P ⩽ 0.005). We conclude that cycles in which serial serum concentrations of E2 follow pattern A in response to stimulation give rise to oocytes that, when fertilized, yield higher cleavage rates and better-quality embryos than oocytes obtained from women in whom serial serum E2 concentrations follow pattern B. This finding is in keeping with the hypothesis that plateau and leap patterns of serial serum E2 concentrations are reflective of synchronous and asynchronous follicular recruitment, respectively.