The legal battle for gender equality gave birth, in the early 1970’s, to a riddle. Faced with the pervasive and profound effect of employer responses to women’s reproductive function on their status and opportunity in the paid workforce, feminist litigators asked how laws or rules based on a capacity unique to women – the capacity to become pregnant and give birth – could be susceptible to challenge under any equality doctrine the courts of this country might realistically be persuaded to employ. In response to that question, the proponents of gender equality developed a theory which has been used with moderate success in scores of cases challenging pregnancy rules under Title VII and, for a time, under the equal protection clause as well. Most of these cases have arisen in the employment context; courts have been asked to compare an employer’s treatment of pregnancy to its treatment of other physical conditions with similar workplace consequences. The approach has been, in the words of the 1978 Pregnancy Discrimination Act (PDA), to require that “women affected by pregnancy, childbirth or related medical conditions… be treated the same for all employment related purposes… as other persons not so affected but similar in their ability or inability to work.”