A literature search provides 83 studies from which 616 comparisons of contingent valuation (CV) to revealed preference (RP) estimates are made. Summary statistics of the CV/RP ratios are provided for the complete dataset, a 5% trimmed dataset, and a weighted dataset that gives equal weight to each study rather than each CV /RP comparison. For the complete dataset, the sample mean CV/RP ratio is 0.89 with a 95% confidence interval [0.81-0.96] and a median of 0.75. For the trimmed and weighted dat:asets, these sumrnarJ statistics are (0.77; [0.74~0.81]; 0.75) and (0.92; [0.81-1.03]; 0.94), respectively. Tne Spearman rank correlation coefficients between the CV and RP estimates for the three datasets are 0.78, 0.88, and 0.92, respectively, with the Pearson correlations a bit larger. Non-parametric density estimates are provided, as well as the results of regressions of the observed CV /RP ratios on the basic RP technique used and the broad class of goods valued.

Normally fertilized human embryos biopsied 3 days after in-vitro fertilization (IVF) have been examined for effects on viability and development in vitro after removal of one or two cells at the 8-cell stage (1/8 and 2/8) from each embryo. A high proportion of 7/8 and 6/8 biopsied and unmanipulated embryos developed to the blastocyst stage between days 5 and 6 (79, 71 and 59%, respectively), and many biopsied embryos (56%) hatched from the zona pellucida in vitro. The viability of biopsied embryos which developed to the blastocyst stage was assessed by daily non-invasive measurement of the uptake of two energy substrates, glucose and pyruvate. Uptake of both substrates was generally lower in 7/8 and 6/8 biopsied embryos but only in proportion to the reduced cellular mass. The total cell number and the numbers of both trophectoderm (TE) and inner cell mass (ICM) cells in biopsied embryos at the blastocyst stage, counted by differential labelling of their nuclei, were also reduced in proportion but the ratio of ICM to TE cells was maintained in both 7/8 and 6/8 biopsied embryos. We conclude that removal of one or two cells at the 8-cell stage, while reducing the cellular mass, does not adversely affect the preimplantation/development of biopsied embryos in vitro and suggest that this approach could be used for preimplantation diagnosis of genetic defects.

Mouse preimplantation embryos consume pyruvate preferentially during the early developmental stages, before glucose becomes the predominant energy substrate in the blastocyst. To investigate the importance of the switch to glucose utilization at the later developmental stages, mouse embryos from F1 hybrid mice (CBA/Ca x C57BL/6) were cultured from the one- and two-cell stages (22 and 46 h post hCG, respectively) for 5 days in a modified medium, M16, containing 0.33 mM pyruvate and 5 or 23 mM D + L-lactate, in the presence and absence of 1 mM glucose (M16 + G and M16 - G, respectively). Nutrient uptakes were also determined over this time. Some embryos cultured in M16 - G were transferred to M16 + G at 94 or 118 h post hCG. Embryos cultured from the two-cell stage in M16 + G exhibited the characteristic fall in pyruvate consumption between the morula and the blastocyst stage; those cultured from the two-cell stage in M16 - G compensated for the lack of glucose by consuming increasing amounts of pyruvate, from 2.78 pmol/embryo/h at 58 h post hCG to 5.21 pmol/embryo/h at 154 h post hCG. However, the percentage of embryos developing to the blastocyst stage, the hatching rate, and blastocyst cell numbers (50.6 +/- 2.5 [28] vs. 105 +/- 3.8 [37]) were all lower in this group. When exposed to glucose at 94 or 118 h post hCG, embryos cultured from the two-cell stage in M16 - G readily consumed glucose in preference to pyruvate, although the characteristic fall in pyruvate consumption was not observed. One-cell embryos cultured continuously in M16 - G were only able to develop to the morula stage, after which time they degenerated. In these embryos pyruvate was readily consumed between 22 and 94 h post hCG, before falling from 2.77 pmol/embryo/h at 83 h post hCG to 0.045 pmol/embryo/h at 130 h post hCG. Transfer of these embryos to M16 + G at 94 and 118 h post hCG did not support development to the hatching blastocyst stage.(ABSTRACT TRUNCATED AT 250 WORDS)

The purpose of this study was to determine the effect of heparin-binding epidermal growth factor (HB-EGF) on human embryo development in vitro from days 2 to 14 post-insemination. Embryos were cultured in a complex serum-free medium (CSFM3) in the absence and presence of 1 nM and 100 nM HB-EGF. Development to the blastocyst stage of A-C-grade embryos (A grade = highest quality) was improved in the presence of 1 nM HB-EGF from 40.7% to 65.4% and significantly increased to 71.0% in the presence of 100 nM HB-EGF (P < 0.05). Moreover, the percentage of blastocysts hatching was improved in the presence of 1 nM HB-EGF from 45.5% to 70.5% and almost doubled to 81.8% (P < 0.05) in the presence of 100 nM HB-EGF. HB-EGF promoted the development of high-grade (classed as BG1) and medium-grade (BG2) blastocysts. There was no difference in blastocyst quality between the control and HB-EGF-treated embryos as assessed by blastocyst cell number and consumption of the major energy substrates, pyruvate and glucose, measured on day 6 of culture. Further development was assessed by culturing the blastocysts on growth factor-reduced Matrigel (GFR-Matrigel). Adherence and outgrowth were observed, with these embryos producing significantly more human chorionic gonadotrophin over days 7-14 compared with those cultured on plastic (47.8 +/- 8.0 mU versus 23.0 +/- 8.6 mU). The addition of recombinant human growth factors to clinical in-vitro fertilization medium may be useful in promoting embryo development with a view to carrying out blastocyst transfers.

A robust model for the study of mechanisms of implantation of the human embryo into the endometrial stroma has been established.

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