F. Other morphological features
F.1 Vacuoles/vacuolation
Vacuoles can arise during in vitro culture of human embryos at any stage of development (Ebner et al., 2005). Those first detected on Day 4 of development have the most severe impact on blastocyst development (Ebner et al., 2005). Vacuoles appearing in early development cannot often be detected within the blastocyst or can be detected only in excluded cells (Ebner et al., 2005). Vacuoles when found within the blastocyst appear more often in the TE than in the ICM (Figs 392–394; Ebner et al., 2005). These vacuoles should be distinguished from degenerative changes or vacuolation described and classified as BG3 blastocysts by Dokras et al., 1993.
Figure 392
Expanded blastocyst (Grade 4:3:2) in which a large vacuole can be seen at the 6 o'clock position between TE cells. The blastocyst was transferred but the outcome is unknown.
Figure 393
Hatching blastocyst (Grade 5:1:1) showing a compact ICM at the 6 o'clock position which is associated with several cellular fragments. The TE is made up of many cells that form a cohesive epithelium but there are two medium-sized vacuoles within TE cells abutting the ICM toward the 9 o'clock position. The blastocyst was transferred but failed to implant.
Figure 394
Early blastocyst (Grade 2) with large vacuolization of the TE distinct from the blastocoel cavity at the 10 o'clock position in this view. The blastocyst was transferred but the outcome is unknown.
F.2 More than one point of natural hatching
A rare finding in blastocyst assessment is the occurrence of two or more sites of hatching (Figs 395–397; 2%; Fong et al., 2001). It has been suggested that this might arise in ICSI-generated blastocysts due to incomplete closure of the zona breach created by the microinjection pipette (Fong et al., 1997). Hatching at more than one point in the ZP, particularly when one of the holes is very small could result in trapping of the blastocyst within the ZP as the pressure within the blastocoel cavity would be dissipated and not concentrated on one hatching site.
Figure 395
Early hatching blastocyst (Grade 5:1:1) which is beginning to hatch naturally from two different small breaches in the ZP. The ICM is large and compact and the TE cells are many and form a cohesive epithelium. The blastocyst was transferred but the outcome is unknown.
Figure 396
Hatching blastocyst (Grade 5:1:1) with a large amount of TE herniating from a breach in the ZP at the 3 o'clock position and a second smaller site of herniation at the 6 o'clock position. The blastocyst developed following ICSI and so the breach in the ZP at the 6 o'clock position may be a result of the injection site. This blastocyst did not result in a pregnancy following transfer.
Figure 397
Hatching blastocyst (Grade 5:1:1) with two distinct points of natural hatching, one at the 11 o'clock and one at the 6 o'clock position. The ICM is large and compact and the TE cells are many and form a cohesive epithelium. There is a significant difference in the diameter of the two breaches in the ZP. The blastocyst developed following standard insemination and so the smaller diameter breach is not a result of sperm injection. The blastocyst was transferred but failed to implant.
Article references:
Ebner T, Moser M, Sommergruber M, Gaiswinkler U, Shebl O, Jesacher K, Tews G. Occurrence and developmental consequences of vacuoles throughout preimplantation development. Fertil Steril 2005;83:1635-1640.
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Fong CY, Bongso A, Ng SC, Anandakumar C, Trounson A, Ratnam S. Ongoing normal pregnancy after transfer of zona-free blastocysts: implications for embryo transfer in the human. Hum Reprod 1997;12:557-560.
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Fong CY, Bongso A, Sathananthan H, Ho J, Ng SC. Ultrastructural observations of enzymatically treated human blastocysts: zona-free blastocyst transfer and rescue of blastocysts with hatching difficulties. Hum Reprod 2001;16:540-546.
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Dokras A, Sargent IL, Barlow DH. Human blastocyst grading: an indicator of developmental potential? Hum Reprod 1993;8:2119-2127.
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