Pregnancy following fertilization of zona-free, coronal cell intact human ova: Case Report

Abstract

A pregnancy by intracytoplasmic sperm injection (ICSI) of a couple whose oocytes were recovered without a zona pellucida is reported. Previous IVF/ICSI cycles indicated all oocytes had either very thin or no zona pellucida at the time of cumulus removal prior to ICSI. As a result, many ova were very fragile and lysed upon handling. In the latest attempt, six ova were recovered. After coronal cell dissection of two ova where both lacked a zona pellucida and one lysed, it was elected to attempt to inject the remaining four ova without removal of their coronal cells. The zona pellucida was not visible through the cell layer and the position of the polar body in three ova was speculative. Two embryos possessed normal pronuclei on day 1, and displayed six blastomeres prior to transfer on day 3. During preparation for transfer, sufficient coronal cells fell away to confirm both embryos lacked a zona pellucida. Pregnancy was confirmed by ultrasound observation of a fetal heart 4 weeks later. This report documents that where the zona pellucida is absent, the coronal cells provide sufficient support to maintain blastomere interaction and embryo viability and the zona pellucida is not essential for early embryo development and pregnancy.

Alteration in the Mechanical Properties of Human Ovum Zona Pellucida Following Fertilization: Experimental and Analytical Studies

“…4 Young's modulus of the human ZP determined using the shell model. Significant differences were found between embryos and oocytes using this model, (p<0.05) tal reasons [49][50][51][52][53]. This was characterized by different deformation when the aspiration pressure was applied and consequently the unlike slope of the negative applied pressure (Δp) versus the equilibrium length of ZP projection to the internal pipette radius (L/r i ) for the oocytes/ embryos of different donors clarified this claim.…”

Intracytoplasmic Sperm Injection – Factors Affecting Fertilization

“…The zonafree oocytes may be fertilized normally after ICSI and develop to the blastocyst stage [165]. Pregnancy in human [166] and live birth in mouse [167] and pig [168] have been obtained after transfer of embryos resulting from zona-free oocytes.…”

Morphological selection of oocytes

“…Since ZP dysmorphisms are probably caused by an altered secretion and/or patterning of the glycoproteic matrix (46), some Authors tried to relate ZP thickness and darkness to oocyte quality. Severe changes in thickness (Figure 16) or the complete lack of ZP are extremely rare (47) and the results are still controversial (1). As to the discoloration degree, it has been postulated that brown zonae can be related to better IVF/ICSI and clinical results such as fertilization rates, embryo quality and pregnancy rates (48).…”