This area is really tough. I feel terrible for women who experience this bias, but the solution is not nearly as obvious as with race/gender/age/religious/etc discrimination. In those cases the answer is: stop being biased.

Let's say you're a small company and you can really only afford to have <10 people on your payroll. Let's say you're considering two candidates of exactly equal skills and age: a 28yo man and a 28yo woman.

Even if they both plan to have 2 kids in the next 4 years, it's a biological reality that it will take the woman away from work for longer. She has the 9 months of pregnancy where she may be tired or uncomfortable, then the actual delivery, then recovery, and then often a period of breast feeding. The man could be father of the century but there are certain burdens that fall on women because of their sex.

So while I'd like to force the startup to make the decision without considering this factor, is that always reasonable?

And before the downvotes come: I am really on the side of pregnant women here. I want them to get generous leave without any effect on their careers. But I am questioning if that is always possible.