In the same vein, many women choose to work part-time so they can be around to look after their children more.
If you are working less, you are going to get paid less. And it goes without saying, part-time jobs are not going to be the high-powered roles which command a high hourly rate - being a part-time chief executive is not usually an option if you want to run a successful business.
It does also come down to what career you choose. Administration jobs, which are often in the lower pay bracket, have been dominated by women. A man doing the same job would get the same pay.
These days women are training for a much wider variety of jobs. I know women who have studied engineering, medicine, law and business - all traditionally high-paying and male-dominated jobs. Given a few more years we may see the gender pay gap declining as these women move towards the top of their fields.
Of course how high you go is down to each individual.
If you choose to take time out to have children, you can't expect to climb through the ranks in the same time as someone who does not take that time off.