Fluorescence in situ hybridization analysis of two blastomeres from day 3 frozen-thawed embryos followed by analysis of the remaining embryo on day 5.
BACKGROUND
Chromosomal mosaicism in human embryos may give rise to false positive or false negative results in preimplantation genetic diagnosis for aneuploidy screening (PGD-AS). Therefore, we have investigated whether the results obtained from a 2-cell biopsy of frozen-thawed embryos and fluorescence in situ hybridization (FISH) analysis are representative for the chromosome constitution of the remaining embryo on day 5.


METHODS
Cryopreserved day 3 embryos were thawed and from surviving embryos two blastomeres were biopsied. FISH analysis was performed for chromosomes 1, 7, 13, 15, 16, 18, 21, 22, X and Y. After biopsy, the embryos were cultured until day 5 and further analysed using the same probe panels.


RESULTS
In all, 17 embryos were available with a diagnosis based on two blastomeres on day 3 and confirmatory studies on day 5. In 10 of these 17 cases the initial diagnosis could be confirmed. However, in only six cases cytogenetic results were concordant. Besides the 10 cases with a 'correct' diagnosis, there were six false positive results and one false negative, all involving mosaicism.


CONCLUSIONS
Investigating the chromosomal constitution of two blastomere nuclei offers a good opportunity to study the incidence of chromosomal mosaicism in early embryo development. The confirmation rate of the results obtained on day 3 depends on the interpretation and is higher when considered from a clinical than from a cytogenetic point of view.
Division of Reproductive Medicine, Department of Obstetrics and Gynaecology, Erasmus Medical Centre, Rotterdam, The Netherlands. e.baart@erasmusmc.nl
E B
EB
Baart
D
D
Van Opstal
F J
FJ
Los
B C J M
BC
Fauser
E
E
Martini
D000782:Aneuploidy; D001706:Biopsy; D001757:Blastomeres / Q000473:pathology*; D002467:Cell Nucleus / Q000648:ultrastructure; D002877:Chromosomes, Human; D015925:Cryopreservation; D046508:Culture Techniques; D004622:Embryo, Mammalian / Q000502:physiology; D005314:Embryonic and Fetal Development; D005188:False Negative Reactions; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D009030:Mosaicism; D019836:Preimplantation Diagnosis