Does the legal definition of a 'mother' suit modern society?

We recently saw the High Court decide that a transgender man who gave birth with the help of fertility treatment cannot be legally registered as the father (or parent) of his child. The case has also provided the first legal definition of a mother.

This case highlighted just one of the difficulties faced by non-traditional families living in today's society where the law as it stands can feel antiquated and sits at odds with the realities of modern life. 

For example a family living near Bristol recently featured in the national press regarding their choice not to reveal their child's sex and to raise them as gender-neutral.  When they became parents Jake and Hobbit decided that this was the only way to mitigate unconscious gender bias and that they will let their child Anoush choose their own gender when they are old enough.

How is a 'mother' currently defined?

The judge in this case the President of the Family Division Sir Andrew MacFarlane has provided the first legal definition of a mother.  He ruled that being a child's "mother" or "father" is not necessarily gender specific and that...