They are female white-collar workers. They didn't have any plan to have a child until the economic crisis struck. Then they decided to get pregnant - as quickly as possible.
They are afraid of getting fired. China's labor law stipulates that a company should not fire a pregnant employee unless the company is insolvent. "Get pregnant as soon as possible" became a mantra at the height of the economic crisis. Indeed, so many female employees made this choice that they were collectively dubbed "the rush-to-get-pregnant tribe".