Sequential analysis of zona thickness during in vitro culture of human zygotes: Correlation with embryo quality, age, and implantation

Abstract

Zona pellucida thickness was measured daily in zygotes and cleavage stage embryos. Measurements were performed on a Nikon inverted microscope equipped with Hoffman modulation optics, using an ocular micrometer. Zona thickness of each zygote/embryo was measured four times, the zygote/embryo was then “rolled over,” and four more measurements were repeated for a total of eight. The zygotes/embryos were photographed daily and the measurements repeated on the prints. Subsequently, the mean zona thickness for each stage was calculated. A total of 81 patients (mean age 33.8 ± 4.2) participated in the study. A total of 427 embryos were evaluated. Categorical data differences between groups were evaluated by ANOVA and multiple linear regression. For nominal data, the Kruskal‐Wallis test was applied; when P < 0.05 the differences were considered to be significant. We found that the average zona thickness on day 1 of in vitro culture was 17.7 ± 0.14 μm; 16.3 ± 0.14 μm on day 2 and 14.9 ± 0.14 μm on day 3 (P < .0001). When the zona thickness was analyzed in relation to the number of blastomeres on day 3 of culture, there was a highly significant correlation with blastomere number (P < .0001). Similarly, there was a highly significant correlation with embryo grade (P < .005) and fragmentation (P < .001). The data were also analyzed for embryos transferred that resulted in a successful pregnancy, revealing that embryos in a pregnancy cycle had significantly thinner zonae pellucidae (P < .0001), when compared to embryos that were not transferred or from nonconceptual cycles. The average zona thickness also decreased with age, and was most apparent after 35 years. Changes in zona thickness correlated with the number of blastomeres, grade, fragmentation, age and were more evident in embryos transferred from cycles resulting in successful pregnancies. Therefore, zona pellucida measurements should be included in the overall assessment of embryo quality, since this information may be useful in the selection of optimal embryos for transfer. Mol. Reprod. Dev. 47:99–104, 1997. © 1997 Wiley‐Liss, Inc.

Clustering of monozygotic twinning in IVF

“…We found an increased incidence of MZT among those pregnancies conceived after extended embryo culture and transfer. The natural thinning of the zona pellucida during the aging process was initially thought to confer additional risk of MZT with increasing maternal age [28]. In our study, however, maternal age did not appear to be a significant risk factor for MZT.…”

Correlation of oocyte morphometry parameters with woman’s age

“…It is to be pointed out, however, that an apparent discrepancy about the average ZPT values exists among different works. This could be due to several factors including different scoring methods, high variability oocytes shape among patients and different culture conditions [26][27][28].…”

Vitrification of isolated human blastomeres

“…blastomere could be caused by the dynamic expression of its osmotic response (15)(16)(17)(18)(19)(20) or the pressure of both the VS and carrier on the surface of the sample, as discussed previously. All zonae included in this study were of a similar thickness (18.2 AE 2.9 mm [mean AE SD] and 12.3-24.5mm [95CI]) within the normal range of 10-31 mm (21). Thickness was not related to survival rate, probably because the presence of a hole in the zona made it completely permeable regardless of its thickness.…”