research day - University of Toronto Department of Obstetrics and ...

96
ABSTRACT #P-L3
IS ZONA PELLUCIDA THICKNESS AN INDICATOR OF EMBRYO IMPLANTATION
POTENTIAL
Siamak Bashar [O], Gelareh Motamedi, Agata Sojecki, Rodica Mandel, Hanna Balakier, and
Clifford Librach
CReATe Fertility Center, Department of Obstetrics and Gynaecology, Sunnybrook Health
Sciences Centre and Women’s College Hospital, University of Toronto.
Objective: Zona pellucida thickness (ZT) and the process of gradual zona thinning have been
suggested to be the most predictive indicators for the implantation potential of transferred embryos.
However, little is known about the intrinsic and external factors that regulate the thinning process
of human zona pellucidae. The objective of our study was to evaluate whether zona pellucida
thickness on day 3 of in vitro culture is correlated with maternal (patient) age, embryo quality, Day
3 FSH, peak estradiol (E2) levels, implantation rate and pregnancy outcome.
Methods: After obtaining REB approval, data on zona thickness and patient clinical parameters
was collected from 360 patients of all ages undergoing IVF or ICSI procedures. Zona pellucida
measurements were performed on all Day 3 embryos (n = 2396) derived from normal zygotes
(normally fertilized oocytes). Zona thickness was classified into 6 categories according to an
ascending range of mean values from 9.0 µm to >=19.1 µm.
Results: No significant correlation was observed between zona thickness and the age of the
patients (P=0.654; Table 1). The overall mean zona thickness was 15.97±2.53 µm and the
embryos with very thin zona pellucida were rare in all age groups. 59 out of 2396 (2.5%) embryos
had a zona thickness in the range of 9.0µm to11.0 µm and 8% of embryos had zona thickness in
the range 11.1 and 13.0µ (212/2396). The majority of embryos ranged between 15.1-19.0 µm
(54.5%). No significant relationship was observed between zona thickness and the maximum E2
value on the day of HCG administration. The proportion of embryos in the six categories of mean
zona thickness was similar regardless of E2 level (P=0.2561). There was also no association
between zona thickness and FSH values on Day 3 of the cycle prior (P-0.3824). A very significant
association was found between zona thickness and individual embryo quality (P=0.0005).
Embryos with no or minimal number of cytoplasmic fragments (0-10%) and equal cell size (G1-
G2; n=1967) had significantly thinner zonae (Av. 15.87µ±2.48) compared with the embryos
containing more fragments and uneven blastomeres (G3 = 16.36µ±2.57 and G4-G5 =
16.59µ±3.06). A total of 137 clinical pregnancies resulted from 360 embryo transfer cycles
(38.1%). Comparison of zona thickness of all transferred embryos between pregnant versus nonpregnant
patients showed no significant differences (15.96 versus 16.97; P =0.5002).
Conclusions: The thickness of the human zona pellucida is not influenced by intrinsic and external
factors such as patient age, day 3 FSH or peak E2 levels. Zona thickness is highly correlated with
embryo quality. It appears that overall zona thickness is not correlated with pregnancy rate,
suggesting that embryo hatching depends more on inherent properties of gametes and the
developmental potential of the resultant fertilized embryos.