why were pregnant women weak individuals and the sick the first to be executed in the Nazi concentration camps

The main reason why this occurred was because the prisoners that were held in the concentration camps were taken there in order to be used as forced labor. The prisoners here were treated badly, ate little, were constantly abused, and worked long hours. Therefore, the Nazi knew that pregnant women, weak individuals, the sick and the old were not going to be able to tolerate this treatment and work efficiently.