Proxy voting in the House of Commons is not a bad idea in principle, and by no means only for maternity or paternity purposes.
But watch out for Cabinet Ministers whose proxy votes were permanently in the hands of the Chief Whip, so that they themselves hardly ever needed to go near the place.
Who would be Caroline Lucas's proxy? Or Sylvia Hermon's? Or, at the moment, Frank Field's?
And none of this answers the question as to who would be the MP for a seat while its MP were off on the maternity leave that does not in fact exist.
This is not the 1970s. If maternity leave for MPs were possible, then it would have been in place for decades.
Giving another MP your proxy vote is no more sufficient than saying that you still had constituency staff to advise callers to try leaving a saucer of milk at the foot of the tree.