I'm for equality, and the area around FMLA is not equal, by any means.
That issue is caused by the risk that women of child-bearing age have with regards to our laws on FMLA. Women (of child bearing age) are an inherent risk with strong legal ramifications if ignored. Once pregnant, they can effectively get up and leave their position. Depending what they were doing, can cause significant team problems. And the employer is required to provide their or a similar position back when they return. I'm sure the actuaries have calculated that risk appropriately.
To fix that, all gov't needs to do is apply FMLA to all parties in a relationship when one in it is pregnant. Then the actuarial cost equals itself out. Equality is approached.