The first time a government worker encouraged Yumi Yang to have a baby, she thought little of it. She and her husband were registering their marriage at a local office in northeastern China, and the worker gave them free prenatal vitamins, which she chalked up to the government trying to be helpful.

When an official later called to ask if she had taken them, and then called again after she did get pregnant to track her progress, Ms. Yang shrugged those questions off as well intentioned, too. But then officials showed up at her door after she had given birth, asking to take a photograph of her with her baby for their files. That was too much.

“When they came to my home, that was really ridiculous,” said Ms. Yang, 28. “I felt a little disgusted.”

Faced with a declining population that threatens economic growth, the Chinese government is responding with a time-tested tactic: inserting itself into this most intimate of choices for women, whether or not to have a child.

Officials are not just going door to door to ask women about their plans. They have partnered with universities to develop courses on having a “positive view of marriage and childbearing.” At high-profile political gatherings, officials are spreading the message wherever they can.