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 ofzona pellucida thickness variation (ZPTV) of transferredembryos with identical morphologies and subsequent clinicalpregnancy rates during 141 intracytoplasmic sperminjection (ICSI) treatment cycles.Methods: A total of 141 women participating in the studygroup comprising mostly male factor infertilities and somerepeat in vitro fertilization (IVF) failures were transferred,2 days after ovum pickup, with two to three embryos withidentical grades created by fertilization with ICSI. Allselected embryos were subjected to zona pellucida thicknessmeasurements immediately prior to transfer using a computerizedembryo measurement program from videocinematographyrecordings.Results: A total of 326 identical-grade transferredpre-embryos resulted in 70 clinical pregnancies with live-bornimplantation rate of 27.6%. A highly significant correlationwas observed between ZPTV of transferred embryos andthe IVF outcome with 77.1% and 83.64% of the clinicalpregnancies resulting from transferred embryos with ZPTVvalues greater than 20 and 25, respectively. The mean ZPTVvalues for 70 conceptual cycles and 62 nonconceptual cycleswere 28 ± 6.43 and 17.85 ± 8.11, respectively. No significantcorrelation between ZP thickness and number of blastomeresin the transferred embryos was evident, though embryoswith better scores had significantly thinner zonae and higherZPTV values. Though average zona thickness of embryosdeclined with age, the mean ZPTV value for women lessthan 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 embryosexhibits a strong correlation with clinical pregnancy outcome following IVF treatment. This potentially reliable indicatorof IVF success rate could be used as a criteria forembryo selection during clinical transfers.