| Summary: | Triploid human embryos are believed to account for up to 20% of all first trimester spontaneous abortions with a numerical chromosomal abnormality. This group of polyploid embryos therefore gives rise to a significant proportion of human pregnancy wastage. It would appear from cytogenetic studies of human triploid conceptuses that 85% of human triploids are of diandric origin and only 15&37 of digynic origin. Some of these genetic conditions are of considerable clinical significance, since the placentas of human diandric diploids and diandric triploids show 'complete' and 'partial' hydatidiform molar degeneration, respectively. Since the number of human triploid conceptuses obtained in any one centre is generally very limited, and their pre- and early post-implantation stages are simply unavailable for analysis, suitable animal models have been developed to study these genetically abnormal conditions. A study of these triploid conditions has been investigated through the analysis of the appropriate mouse models produced by the expermental techniques indicated below. The relationship between the genetic constitution, morphological appearance and developmental fate of these various types of triploid embryos has been investigated in this study. One of the most informative models we have used is the LT/Sv strin of mice, which regularly ovulate primary oocytes, which are capable to being fertilised and produce digynic triploid embryos. We have also shown that by the administration of exogenous hormones to this strain of mouse the incidence of ovulation of primary oocytes can be increased. It has also been observed that maternal age of the mouse was important in relation to the incidence of primary oocytes ovulated; at 6 weeks old up to 50% of the oocytes ovulated were primary oocytes, significantly lower levels were observed when females were examined at 12, 18, 24 and 30 weeks of age. We have also been able to produce digynic triploid embryos in F1 hybrid female mice by the administration of an intraperitoneal injection of cytochalasin D, which if given at an appropriate time after Human Chorionic Gonadotrophin (HCG) administration, will inhibit the extrusion of the second polar body following fertilisation, and result in the production of up to 18% of digynic triploids.
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