In a new paper, Female Employment and Fertility - The Effects of Rising Female Wages (July 2012), Christian Siegel, writes:
Increases in female employment and falling fertility rates have often been linked to rising female wages. However, over the last 30 years the US total fertility rate has been fairly stable while female wages have continued to grow. Over the same period, we observe that women's hours spent on housework have declined, but men's have increased.
The paper shows the stable evolution of the fertility rate and the decreasing gender wage gap (by 2005 the average women wage was around 77% of the average male wage, it was around 60% in the late 1960s).