"Don't forget ONCE UPON A MATTRESS, the entire plot of which hinges on the unplanned pregnancy of an unmarried woman played for laughs. That was a few years after AUNTIE MAME and a few years before MAME."
Ha! Good point. But I would say that is quite a different situation from the others, as Sir Harry and Lady Larken are very much in love with each other, and when they learn that she's pregnant, they wouldn't hesitate to get married except that everyone in the land is forbidden to marry until Prince Dauntless finds a bride.