Influence of zona pellucida thickness of human embryos on clinical pregnancy outcome following in vitro fertilization treatment

Purpose: To evaluate the correlation between the degree of zona pellucida thickness variation (ZPTV) of transferred embryos with identical morphologies and subsequent clinical pregnancy rates during 141 intracytoplasmic sperm injection (ICSI) treatment cycles. Methods: A total of 141 women participating in the study group comprising mostly male factor infertilities and some repent in vitro fertilization (IVF) failures were transferred 2 days after ovum pickup, with two to three embryos with identical grades created by fertilization with ICSI. All selected embryos were subjected to zona pellucida thickness measurements immediately prior to transfer using a computerized embryo measurement program from videocinematography recordings. Results: A total of 326 identical-grade transferred preembryos resulted in 70 clinical pregnancies with live-born implantation rate of 27.6%. A highly significant correlation was observed between ZPTV of transferred embryos and the IVF outcome with 77.1% and 83.64% of the clinical pregnancies resulting from transferred embryos with ZPTV values greater than 20 and 25, respectively. The mean ZPTV values for 70 conceptual cycles and 62 nonconceptual cycles were 25 +/- 6.43 and 17.85 +/- 8.11, respectively. No significant correlation between ZP thickness and number of blastomeres in the transferred embryos was evident, though embryos with better scores had significantly thinner zonae and higher ZPTV values. Though average zona thickness of embryos declined with age, the mean ZPTV value for women less than 30 years old was significantly higher (25.84 +/- 8.57) as compared with those from women older than 35 years (20.72 +/- 8.45). Conclusions: The degree of ZPTV of the transferred embryos exhibits a strong correlation with clinical pregnancy outcome following IVF treatment. This potentially reliable indicator of IVF success rate could be used as a criteria for embryo selection during clinical transfers.