It's not clear from the actual results in the study if number of pregnancies is the factor, or just simply having at least one pregnancy and experiencing matrescence. The summary seems to suggest its number of pregnancies, but I'm not seeing the data. Maybe I didn't look in the right place. An interesting follow up study would be to look at women who had one pregnancy that failed more than halfway through.

Anecdote: My first pregnancy, and matrescence significantly aged me. But my second pregnancy, which was actually more challenging, seemed to have almost no effect on how old I felt and looked.