first.diff.fitted
In catregs: Post-Estimation Functions for Generalized Linear Mixed Models

Computes the first difference in fitted values, or a series of first differences, from an estimated regression model. Inference in supported via the delta method or bootstrapping.

For example:

library(catregs)
data("Mize19AH")
m1 <- glm(alcB ~woman*parrole + age + race2 + race3 + race4 + income + ed1 + ed2 + ed3 + ed4,family="binomial",data=Mize19AH)
des2<-margins.des(m1,expand.grid(woman=c(0,1),parrole=c(0,1)))
des2
first.diff.fitted(m1,des2,compare=c(4,2)) # Pr(Drink | Mothers) - Pr(Drink | Childless Women)
first.diff.fitted(m1,des2,compare=c(3,1)) # Pr(Drink | Fathers) - Pr(Drink | Childless Men)