Most couples choose artificial insemination. They feel it unbearable to pretend to make love just because of the Four Children Policy. China needs Chinese, and the State's punishments are sometimes subtle and always painful, but there's some bitter satisfaction in denying them this.
Everybody knows the Policy doesn't work anyway. China is one huge factory, too harsh an environment for an unwanted pregnancy to succeed. Miscarriages are the rule, sometimes followed by death, but the anguish that follows --- because how could it not, regardless? --- and each empty train seat are in themselves a form of defiance.