AssassinatedB : "You don't think that there should or could be a way to reduce the impact of maternity on women at work?"
Well, so long as we don't get it muddled up with the original subject which was the gender pay gap and how much of it has to do with discrimination...
...I'm mostly a free market sort of person, and so I think that employers will usually have an interest in accommodating their valuable female employees when it comes to maternity and childcare. But the extent to which such accommodation is valuable will depend on the value of the female employee to the employer. So if you're a top notch banker or lawyer, or business manager, your employer will do more or less anything to accommodate you because you're worth a lot of money to them. (I'll mention though that my own experience in this area is slightly discouraging. For my sins I used to work in a place where we had lots of very high powered high quality female employees, and we bent over backwards organisationally and financially to accommodate maternity and child care. But more than 75% of the time, once the baby popped out, the mother did not want to come back to work, either at all, or as a full time employee. And these were women who loved their jobs and were absolutely convinced, pre baby, that they were definitely coming back to work. Actual babies can change your perspective.) Whereas if you're a cashier in the supermarket you're not worth very much. You're easy to replace cheaply. And then depending on your business, it may be very easy or very difficult to accommodate female employees and their maternity plans. So holding a job open for a female employee is usually very easy for a large employer (unless she has a critical specialist job where you need to hire a replacement.) But holding jobs open in small companies can be really difficult. You just don't have the flexibility. You've got nine employees, five of them women, two get pregnant - what do you do ? If you hire two replacements when the first two get back you've got 20% excess staff. If you don't hire replacements your other workers have got 20% extra work to do. So a market solution is to let different employers make whatever arrangements fit their business.
The consequences would likely be greater job differentiation. Women who wanted children would gravitate to employers who offered good maternity arrangements and away from employers who didn't. I recognise however that such a laissez faire approach would never be allowed in the real political world.
"And what of the fact that more women do childcare? Is that just a simple choice which men and women make equally? So any disparity is down to more women simply wanting to do childcare than men?"
Loads of different reasons, some of which is free choice, some of which is pretty much dictated by nature, and some of which is influenced by female mate choice. So if you have a baby without having a regular partner, then you're kinda left holding the baby. And if you make a "typical" choice of a man of roughly your educational level and job prospects, but who is 5 years older than you (and therefore 5 years higher up the ladder) on average it's going to cost your family less if your career comes second to his.
For what it's worth there are studies showing that in families where Mum has the good job, and Dad is the stay at home househusband, Mum still finishes up spending more hours on childcare than Dad ! (On average.) So if you want to tilt at the windmill of unequal child care, good luck.