Can soluble human leucocyte antigen-G predict successful   pregnancy in assisted reproductive technology?
OBJECTIVE
To review the predictive value of soluble human leucocyte antigen-G (HLA-G) in embryo culture fluid for implantation, considering origin, structure, function and detection method of soluble HLA-G.


RESULTS
Soluble HLA-G in embryo culture supernatant has been proposed as a noninvasive marker for the selection of embryos with implantation potential. Controversially, some centres detect soluble HLA-G in none of the culture supernatants of embryos that evolve towards pregnancy, whereas others report it to be mandatory. According to a recently published meta-analysis, the pooled diagnostic accuracy for predicting clinical pregnancy is low. Factors influencing soluble HLA-G results are numerous, for example, embryo culture (single or multiple, washing/denudation steps, medium, day 2 to 5 sample collection), sample preservation to prevent degradation and HLA-G immunoassays (standard, detection limit, reproducibility). Published studies are very heterogeneous. Moreover, the origin of soluble HLA-G in embryo culture fluid is unresolved. From the embryonic genome activation at day 3 onwards, the embryo should be able to produce HLA-G. Before, it is maternally derived, either from the oocyte, follicular fluid or follicular cells contaminating embryo culture.


CONCLUSIONS
At present, no studies have been published on the relationship between pregnancy and soluble HLA-G in supernatants from individually cultured and individually transferred embryos using standardized embryo culture and soluble HLA-G immunoassay, sensitive at the picogram level. As such, it remains undetermined whether the pregnancy is induced by an HLA-G-producing embryo. Therefore, the predictive value of soluble HLA-G in embryo culture supernatant for selection of embryos with good implantation potential remains unknown.
Vercammen
Martine
M
Laboratory of Haematology, Universitair Ziekenhuis Brussel (UZ Brussel), Laarbeeklaan 101,Brussels 1090 , Belgium. martine.vercammen@uzbrussel.be
Verloes
An
A
Haentjens
Patrick
P
Van de Velde
Hilde
H
D015415:Biomarkers; D018920:Coculture Techniques; D003470:Culture Media / Q000032:analysis; D046149:Embryo Culture Techniques / Q000379:methods*; D010064:Embryo Implantation; D004624:Embryo Transfer / Q000379:methods*; D005260:Female; D006680:HLA Antigens / Q000032:analysis*; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I / Q000032:analysis*; D006801:Humans; D011237:Predictive Value of Tests
D015415:Biomarkers; D003470:Culture Media; D006680:HLA Antigens; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I