The approach of immediately retransferring retained embryos does not solve the problem of reduced pregnancy rates in FFA cases. It is suggested that ET should be repeated 1 day later in FFA cases in an attempt to improve pregnancy rates.

No abstract

The G-and C-band chromosome patterns and the location of the nucleolus organizer regions (NORs) are presented for A. namaquensis (2n = 24), A. granti (2n = 32) and A. chrysophilus (2n = 44; 2n = 50). The presence of two distinct cytotypes in what is conventionally recognized as A. chrysophilus is indicative of the presence of two discrete species which, karyology apart, appear to be indistinguishable using existing identification keys. The chromosomal relationships of the South African species and the taxonomic implications of these data are discussed.

Six factorial experiments were conducted to examine the effects of concentra tion of tris(hydroxymethyl)aminomethane (Tris) and type and concentration of sugar in the freezing diluent, and of composition of thawing solution on the survival of ram spermatozoa following the freeze-thaw procedure.Spermatozoa tolerated a relatively wide range in concentration of Tris, but the cell survival varied depending on the type of sugar included in the Tris diluent and on the composition of the thawing solution. Inclusion of sugar in the freezjng diluent was beneficial with glucose a more suitable component than fructose, lactose, or raffinose. When the latter sugars were included in the freezing diluent, the choice of thawing solution was more critical than for the Tris-glucose diluent.The best results were obtained using Tris (300 mM)-glucose (27·75 mM)-yolk (15% vjv)-glycerol (5% vjv) freezing diluent (dilution 1 : 4, semen: diluent) and Tris (300 mM i-fructose (55·5 mM) thawing solution (dilution ratio 1 : 3, pellets: thawing solution, vjv).

The cumulative embryo score system involves three aspects of relevance in pregnancy achievement during in-vitro fertilization (IVF) and embryo transfer: cleavage rates, morphological qualities and the number of embryos transferred. The scores of 602 IVF/embryo transfer trials were calculated and analysed to determine the system's relationship to pregnancy rate, pregnancy outcome and the incidence of twin and triplet pregnancies. The system was also applied to cycles where endotoxins were either present in or absent from culture medium, in order to evaluate its validity in quality control analyses. Pregnancy rates were found to increase from 4%, with scores between 1 and 10, to 35% in the 41-50 group. The score of 20 was the criterion for separating patients into poor and good pregnancy prognosis groups (P = 0.00001). Biochemical abortions occurred more frequently with scores < 20 (P = 0.00978), but a similar relationship was not found in clinical abortion rates (P = 0.62206). Birth rates below and above a score of 20 (2.8 and 19.2%, respectively) differed significantly (P = 0.0005). The scores of twins overlapped extensively with those of singleton births, but those of all triplets were > 40. The system did not reflect a correlation between embryo quality and the presence of endotoxins in culture medium.