Labor Secretary Hilda Solis and President Barack Obama (AP Photo/J. Scott Applewhite)

(CNSNews.com) - 324,000 women dropped out of the nation’s civilian labor force in March and April as the number of women not in the labor force hit an all-time historical high of 53,321,000, according to the Bureau of Labor Statistics.

The civilian labor force consists of all people in the United States 16 years or older who are not in the military, a prison, or another institution such as a nursing home or mental hospital and who either have a job or are unemployed but have actively sought work in the previous four weeks and are currently available to work.

The civilian labor force is a subset of what BLS calls the civilian noninstitutional population, which includes all people in the country 16 or older who are not in the military, a prison, or another institution such as a nursing home or mental hospital.

This year (in both January and April), only 57.6 percent of the women in the civilian noninstitutional population were in the labor force. That is the lowest rate of labor force participation by American women since April 1993, according to historical data maintained by BLS.

The rate of female participation in the civilian workforce peaked twelve years ago--in April 2000--when hit 60.3 percent.

In February, according to BLS’s seasonally adjusted data, 52,833,000 American women were not in the labor force. In March that climbed to 53,090,000—a one-month increase of 257,000. In April, it climbed again to the historical high of 53,321,000—a one-month increase of 231,000 from March and a two-month increase of 488,000 from February.

In February, there was an historical high of 72,706,000 women in the labor force. But in March, that dropped to 72,529,000—a decline of 177,000. And in April, it dropped to 72,382,000—a decline of another 147,000.

Thus, in March and April, according to the BLS data, a total of 324,000 American women dropped out of the civilian labor force.

The number of women added to those not in the labor force in March and April (488,000) exceeds the number of women who dropped out of the labor force during those two months (324,000) because women who newly turned 16, or left the military, or were released from prison or another institution during those two months and then did not seek a job were added to the ranks of those not in the labor force.

BLS says that for a one-month change in the number of women in the labor force to be statistically significant it has to be greater than about 260,000. For a three-month change to be statistically significant it has to be greater than 400,000. Thus, the two-month increase of 488,000 in the number of women not in the labor force is a statistically significant trend, but the two-month increase of 324,000 women who dropped out of the labor force is not. However, if at least 76,000 additional women drop out of the labor force in May the trend will become statistically significant.

Moreover, BLS says the decline of female participation in the workforce over the past year has been statistically significant—dropping from 58.3 percent in April 2011 to 57.6 percent this April.

For both males and females combined, the rate of participation in the labor force dropped to 63.6 percent in April—the lowest rate since December 1981.

Recently, however, women have been leaving the labor force in larger numbers than men.

From February to March, the number of men in the labor force actually increased by 14,000—rising from 82,165,000 to 82,179,000, according to BLS. From March to April, it dropped back down to 81,983,000—a one-month decline of 196,000.