It was German measles parties before the vaccine was developed. It was well known that if a woman caught German measles in the first three months of pregnancy there was a high risk that the baby would have serious problems (congenital rubella syndrome). So why risk your daughter getting measles when she was pregnant - make sure she got it as a child. And the best way to make sure all girls caught it was to bring the as yet uninfected girls in contact with another child who had it.
In the 1980s when I was pregnant with my first child, all pregnant women were tested to see if they'd had German measles (I had) and if they hadn't, they were offered the vaccine. One man my husband worked with was very concerned when his wife became pregnant with their 4th child. She had been tested with her first, which showed she had not had German measles but she refused the vaccine. While in the early stages with her 4th, the child next door came down with the disease. Luckily, she didn't catch it.
