Significado de "at play"

Olá pessoal,

Como eu poderia traduzir as palavras em negrito abaixo ?

The new factor at play, the report said is the change in the trend in the female participation rate, which has edged down on balance since 2000 after having risen for five decades.

But now, she said the increase in participation of women in their prime child-bearing years is largely over.

Obrigado.