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Gestation length and litter size at birth were also used as covariates in the analysis of birth weights. For weaning and Day-56 weights, the true age of each litter when measurements were recorded was used as a covariate. In addition, the numbers of piglets weighing more than (large) and less than (small) the mean piglet birth weight for the control gilts were determined for each litter, and the effect of treatment on the number of large and small piglets per litter was analyzed by ANOVA. Piglets were divided into birth weight classes ranging from >2250 g to <500 g (in 250-g increments), and the frequency of stillbirth and death by the time of weaning was calculated for each weight class. The frequency of stillbirth and death before weaning for piglets was calculated for each gilt, and these frequency data were analyzed using an ANOVA with the effect of gilt and piglet size class as main effects. In experiment 3, the average conceptus diameter and coefficient of variation (CV) was calculated for each litter. Six of 42 gilts (1 control, 3 treated with 100 mg mifepristone, and 2 treated with 200 mg mifepristone) had filamentous embryos, and the average conceptus diameter for these gilts was arbitrarily set to 10 mm (no CV could be calculated for these gilts). All other pregnant gilts contained spherical blastocysts. Average conceptus diameter, CV, total intrauterine protein, and total intrauterine acid phosphatase were analyzed by ANOVA using a model that included the effect of treatment. To more fully evaluate the effect of the different doses of mifepristone, each dose group was compared to the no-treatment control using separate nonorthogonal contrasts.