Is the zona pellucida thickness of human embryos influenced by women's age and hormonal levels?

Objective To evaluate whether zona pellucida thickness (ZPT) of human embryos is correlated with maternal age, patient's hormonal status, embryo quality, and IVF outcomes. Design Prospective study. Setting University-affiliated IVF clinic. Patient(s) Couples undergoing IVF-ET cycles. Intervention(s) Zona measurements, clinical data collection. Main Outcome Measure(s) Correlation between the ZPT and maternal age, basal FSH and E2 levels, stimulation protocols, cause of infertility, embryo quality, and implantation/pregnancy rates. Result(s) The measurements of ZPT were collected from 5,184 day 3 human embryos originated from 744 IVF patients. The overall mean ZPT was 16.18 ± 2.00 μm. No significant correlation was observed between the ZPT and the patient's age, E2 values on the day of hCG administration, basal concentration of serum FSH, stimulation protocol, infertility diagnosis, and implantation/pregnancy rates. The ZPT was strongly influenced only by the embryo quality: Embryos with good morphology exhibited considerably thinner ZP compared with those of less favorable morphology (mean 15.87 ± 2.48 μm vs. 16.36 ± 2.57 μm, respectively). The ZPT had no significant impact on the implantation and pregnancy rates. Conclusion(s) The thickness of the human ZP of day 3 embryos is not influenced by women's age and hormonal levels. The strong correlation between ZPT and embryo quality suggests that thickness of ZP depends on inherent embryo properties. The overall ZPT is not a good predictive indicator for IVF clinical outcomes.