I am doing some regression analysis on a stratified sample where the stratification variable is the dependent variable. Do I need to adjust the regression or the results to account for the disproportionate subpopulations at all?

In other words, I have a sample containing groups A and B where B is very rare in the population but relatively common in the sample. Are the results of a regression on "Group" valid as they are, or do they need to be adjusted to reduce the effect of B members?