A core difficulty with using equality doctrine to protect women’s rights is that the U.S. Supreme Court has ruled that pregnancy-based discrimination is not per se gender-based discrimination under the Equal Protection Clause of the U.S. Constitution. In its landmark decision, Geduldig v. Aiello, the Court ruled that a state-run disability plan that excluded normal pregnancy from coverage did not discriminate on the basis of gender. In the Court’s words:
While it is true that only women can become pregnant, it does not follow that every legislative classification concerning pregnancy is a sex-based classification. . .The lack of identity between the excluded disability and gender as such under this insurance program becomes clear upon the most cursory analysis. The program divides potential recipients into two groups – pregnant women and nonpregnant persons. While the first group is exclusively female, the second includes members of both sexes.
If the first group, pregnant persons, had included both men and women, the Court would have found it easier to evaluate whether gender-based discrimination was taking place, because it then could have determined whether pregnant women were being treated with greater disfavor than pregnant men. But of course, men by definition do not get pregnant.