That's reproductive sex.

The question of classifying human births is larger - not all humans born have gametes. Some have two sets.

For people interested in actual observed birth cases there's a lot more going on than a moronically over simplified two buckets cover all cases when it comes to attributing sex [] .. clearly M or clearly F with everything aligned (physical form + chromosones + gamates) covers most cases .. and then there's the rest.

It gets even broader when including mammals such as rabbits and pigs as they express cases that are potentially possible in humans but not (as yet) observed or on record.

> so it must fundamentally be based on gametes.

Wishful thinking stemming from a strong held preconceived idea of how the workd must be rather than field based observation of that which occurs.