1. Your lack of understanding of mammalian biology is apalling.
2. But there is discrimination aplenty here. This perk is for YOUNG(ish) people of child-bearing age. These people are presumably healthy too. As they can no longer work from home, they are presumably not handicapped to the extent that commuting is difficult for them, and do not have dependents with disabilities at home. As high-tech places tend to encourage way more than 40 hours per week, these young, healthy people tend to burn out as they get older. As they burn out and leave the company, Yahoo keeps a young employee profile, reducing their health insurance costs, saving them more than the cost of the perk.
So we have age discrimination, not sex discrimination.