Are there any partners who have an interest in family friendly or flexible working policies? Do they have any involvement in preferred employer / equal opportunity awards or organisations that champion these subjects? If not, I suspect any comments might be a waste of effort.
I am unclear from you post whether your boss or another partner made the.comments. If it was your boss, do arrange a meeting and said that you are concerned about his comments, how his beliefs impact his opinion towards you and your future career.
Point out that you have been no less productive / effective since you have become pregnant, you have made every effort to ensure your work is covered in your absence but appreciate it is difficult to recruit maternity cover at your level. In fact it sounds like they haven't filled your position during maternity leave which is crazy!
Reiterate your commitment to your job on your return. Being a woman in a world where men work long hours and see presence as an indication of performance is difficult.
He is probably already anticipating your next maternity leave and a succession of events where you need to leave work early to collect children from childcare, stay home with and ill child, have a few hours off for a show.
Does he have children? Who covered all of these things in his family? Who will be responsible for these things in your family?
Answers to these questions will inform the best response to his comments. If he has a stay at home wife, he may be unable to see how working parents can function. If you have a stay at home partner or one who will take at least 50% responsibility for supporting the family or you plan to have a long hours nanny, these facts might reassure him that the picture will not change much on your return from maternity leave.