Background: Several parameters of early embryo development are known as predictors of implantation success. Recently, zygote or embryo morphological assessments are thought to be a major method of selection in embryo transfer. We expected that the concentrations of the steroids in follicular fluid (FF) were associated with oocyte maturation and embryo quality. In the present paper, we evaluated the relationship of several parameters. Methods: We investigated 105 samples of FF from 22 subjects by in vitro fertilization (IVF). We evaluated the correlations between the FF concentrations of estradiol (E2) and progesterone (P4), the diameter of the ovarian follicles, fertilization, and zygote assessment based on pronuclear morphology and day 3 embryo qualities (i.e. number of blastomeres and fragmentation rate). Results: There was a positive correlation between the E2 concentrations in FF and serum (r = 0.273, P < 0.01), but there was no correlation between follicular diameter and the FF concentration of each steroid. The concentration of E2 in FF containing fertilized oocytes was not significantly different from that in FF containing unfertilized oocytes. At the pronuclear stage, the concentration of either steroid in FF did not differ among the morphological groups. The concentration of P4 in FF was significantly lower in the group in which pronuclei were detected at 20 h after insemination than in the group in which pronuclei were not detected. The concentration of E2 in FF was significantly related to the number of blastomeres (r = 0.271, P < 0.05) and furthermore, was significantly higher in FF from which morphologically good embryos were obtained at day 3 (P < 0.05). Conclusions: The FF concentrations of the steroids did not affect the pronuclear pattern, but P4 production may play a role in reducing the potential of the oocyte to develop pronuclei and the concentration of E2 may predict the cleavage capability of the oocyte. (Reprod Med Biol 2003; 2: 171-176).
Keywords: embryo quality; follicular fluid; in vitro fertilization and embryo transfer; steroids; zygote assessment.