I think we read that line differently. My understanding was that
biological mothers were given the standard 6 + an extra 6 + more if needed. They actually come out a bit ahead here, but it's still only 3 months.
The company’s current policy — which went into effect this
year — gives six weeks of paid caregiving leave to all new
parents. Biological mothers receive another six weeks of
leave, and more if they have additional medical needs.
Quoted so people know what we're referring to. The sentence on biological mothers describes two things. The extra six weeks for being the biological mother, and additional time as needed (with some limits, but probably covered under insurance at this point) for medical conditions.